Department of Electronics and Communication Engineering VII Semester R2008 Regulation EMBEDDED SYSTEMS (2 Marks - Question Bank)

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1 Department of Electronics and Communication Engineering VII Semester R2008 Regulation EMBEDDED SYSTEMS (2 Marks - Question Bank) Prepared by Ms.D.Kavitha Ms.G.Vijayakumari Assistant Professor Department of ECE CCET, Puliyur C.F

2 EMBEDDED SYSTEMS UNIT I ARCHITECTURE OF EMBEDDED SYSTEMS 9 Categories of Embedded Systems-Specifications of Embedded systems-resent trends in Embedded Systems-Hardware Architecture-Software Architecture-Communication software-process of generation of executable image-development/testing tools. UNIT II PROGRAMMING FOR EMBEDDED SYSTEMS 9 Getting the most of C-data types-manipulating bits in memory and I/O ports-accessing memory mapped I/O devices structures-variant access-mixing C to assembly-register usage-use of addressing options-instruction sequencing procedure call and return-parameter passing retrieving parameters memory management-scope-automatic allocation-static allocation-dynamic allocation shared memory-recognizing shared objects-reentrant functions-accessing shared memory device drivers- productivity tools. UNIT III HARDWARE PLATFORM 9 PIC microcontroller- Architecture of PIC 16c6x/7x- FSR- Reset action- Oscillatory connection- Memory organization- Instructions- Addressing modes- I/O ports- Interrupts-Timers- ADC- Assembly language programming. UNIT IV REAL-TIME OPERATING SYSTEM CONCEPTS 9 Architecture of the Kernel-task and task scheduler-interrupt Service Routines- Semaphores-Mutex- Mailboxes-Message Queues-Event Registers-Pipes-Signals-Timers-Memory Management Priority Inversion Problem UNIT V REAL-TIME OPERATING SYSTEM TOOLS AND CASE STUDIES 9 Use of µc/os-ii- Case study of coding for an Automatic Chocolate Vending Machine using MUCOS RTOS- Case study of an Embedded system for an Adaptive Cruise Control Systems in a Car- Case study of an Embedded Systems for a Smart Card. TOTAL: 45 TUTORIAL : 15 TEXT BOOKS: 1. K.V.K.K.Prasad Embedded /Real-Time Systems: Concepts, Design and Programming Dream tech, Ajay V Deshmukh Microcontroller Theory and Applications Tata McGraw Hill 2005 REFERENCES: 3. Raj Kamal Embedded Systems Architecture Programming and Design 2/e TMH, David E Simon An Embedded Software Primer Pearson Education Daniel 5.W Lewis, Fundamentals of Embedded Software Pearson Education Peatman Designing with PIC Micro Controller, Pearson 2003

3 UNIT I ARCHITECTURE OF EMBEDDED SYSTEMS Embedded Systems-QB 1. Define Embedded System. An embedded system is one that has computer hardware with software embedded on it and designed for a specific task. An embedded system can be defined as a computing device that does a specific focused job. Applications such as the air conditioner, VCD player, printer, fax machine, etc. are some of the examples of embedded system. Each of these applications will have a processor and special hardware to meet the specific requirement of the application along with embedded software that is executed by the processor for meeting that specific requirement. 2. List application areas of Embedded Systems. Various application areas of embedded systems are... Consumer appliances Office automation Industrial automation Medical electronics Computer networking Telecommunication Wireless technologies Instrumentation Security Finance 3. What are the different categories of embedded system? Based on the functionality and performance requirements, embedded systems can be categorized as Stand-alone embedded systems. Eg. AC, Oven, CD player, TV. Real-time systems. Eg. Aircraft control, Missile & Satellite control Networked Information appliances. Eg. Weather monitoring system Mobile Devices. Eg. PDAs, Smart phones. 4. What are the classifications of Embedded system? Based on complexity of hardware and software, size and capability, the embedded systems are classified as follows. Small scale Embedded System Medium scale Embedded System Sophisticated Embedded System.

4 5. Give examples for Small, Medium & sophisticated scale embedded systems. Small Scale Embedded System Automatic chocolate vending machine Stepper motor controller for a robotics system Washing or cooking system Multitasking toys Medium Scale Embedded System Computer Networking Systems Entertainment systems Embedded firewall / Router Signal tracking system Sophisticated Scale Embedded System Embedded system s for wireless LAN & for convergent technology devices. Security products & high speed network security, gigabit rate encryption rate products Embedded system for real time video & speech 6. List the specialties of embedded systems. As compared to desktop computers, workstations or mainframes, embedded systems have many specialties. Developers need to keep these specialties in mind while designing embedded systems. They are, Reliability Performance Power consumption Cost Size Limited user interface Software upgradation capability 7. List the factors to be considered while evaluating the processor for embedded system. Clock Speed Width and Number of Registers Width of Data and Address bus Internal RAM & ROM Interrupt lines On-chip peripherals such as Timers, UART, ADC, DAC, etc. 8. What are the hardware components of embedded systems? Processor Memory Timers & Interrupt Controller Serial/Parallel Ports Input devices, Interfacing/Driver circuits Output Interfacing/Driver circuits Power supply, Reset & Oscillator circuits.

5 9. Define processor. A processor is a IC, which is capable of performing an arithmetic or logical operation on a given data as per the command given to it. 10. Compare CISC and RISC processor. CISC: Complex Instruction Set Computer (CISC) Aim of designing CISC processor is to reduce the software complexity by increasing the complexity of the processor architecture. CISC has large no of instructions. With less instructions, a task can be performed and hence, the memory requirement in less. No. of registers are available in CISC processor is very less. Eg. Intel x86 family and Motorola series processors. RISC: Reduced Instruction Set Computer (RISC) RISC has limited no. of instructions and hence, complex operation is carried out through sequence of more simple instructions. Large number of registers is required in RISC processor. Another important feature of RISC processor is pipelined instruction execution. Embedded systems generally use RISC processor. Eg. ARM, ATMEL, AVR, MIPS, Microchip s PIC family processors, Power PC and Sun SPARC processor. 11. What are the three processor architectures in embedded systems? Von-Neuman Architecture: This architecture has common memory for both data and program codes.

6 Harvard Architecture: Embedded Systems-QB In this architecture, there are separate memories blocks, one is program memory and the other is data memory. Program memory stores only instructions and data memory stores only data. Two pairs of data buses are used between CPU and the memory blocks. Super Harvard Architecture: The super Harvard architecture (SHARC) is a slight, but significant modification of the Harvard architecture. In Harvard architecture, the data memory is accessed more frequently than the program memory. Therefore, in SHARC, provision has been made to store some secondary data in the program memory to balance the load on both memory blocks. 12. What is Microcontroller? A microcontroller is a single IC with a processor and several other on-chip peripherals such as RAM, ROM, Comm. Ports, TIMERS, ADC/DAC, etc. Compact size of microcontroller suits the requirements for embedded systems and hence widely used in most of the embedded applications. 13. What are the functional blocks of a microcontroller? The functional circuits of a microcontroller are, Processor internal RAM for Data & stack Timers & Watchdog timer ROM / PROM / EPROM External Memories Interfaces I/O Ports Control & Interfaces / Drivers Serial UART communication port 14. What are the features of DSP? A DSP provides fast, discrete-time, signal processing instructions. It has very large instruction word (VLIW) processing capabilities, it processes Single Instruction Multiple Data (SIMD) instructions fast, and it processes Discrete Cosine Transformations (DCTs) and inverse DCTs (IDTs) fast.

7 15. What is GPP & ASIP? GPP: A processor from a number of families of processors, microcontroller, embedded processors and DSPs having a general purpose instruction set and readily available compilers to enable programming in a high level language is called a General Purpose Processor (GPP). ASIP: A processor designed for specific application on a VLSI chip is called an Application Specific Instruction Processor. 16. What is ASSP? Application Specific System Processor is a processing unit for specific tasks, foe e.g. Image compression and that is integrated through the buses with the main processor in an embedded system. 17. What is System-On-Chip? A complete system on a single VLSI chip that comprises of all needed analog as well as digital circuits in it. For example, mobile phone. 18. What are the various forms of system memories? Internal RAM Internal ROM / PROM /EPROM External RAM External ROM / PROM Internal & External Caches Hybrid memory such as E 2 PROM, NV-RAM or flash memory 19. List the important sensors and transducers. Temperature Sensors. Eg. AD22100, AD22103, DS18B20 Light Sensors. Eg. TAOS TSL250R Accelerometers. Eg. ADXL 150/250 Pressure Sensors. Eg. MPXA 6115A Microphone and Speakers Video camera and Monitor 20. List the important types of Displays. Light Emitting Diode (LED) Liquid Crystal Display (LCD) Thin Film Transistor (TFT) Display Organic Light Emitting Diode (OLED) 21. List the important Serial communication protocols. Inter-integrated Circuit (I 2 C) Serial Peripheral Interface (SPI) Universal Serial Bus (USB) Controller Area Network (CAN)

8 22. List the important communication interfaces used in embedded systems. Serial interface using RS232 Serial interface using RS422/RS485 Universal Serial Bus (USB) Infrared Ethernet Wireless interface using IEEE (WLAN) Bluetooth ZigBee IEEE Embedded Systems-QB 23. Define interrupt handler. It is a unit that handles the processor operations arising out of an interrupt from a source. 24. What is watchdog timer? It is a timer which resets the processor in case the program gets struck for an unexpected time, with the help of timeout signal. 25. What is reset circuit and power-up reset? The reset circuit activates for a fixed period and then deactivates. It helps the processor to start the processing of instructions from a starting address. Power-up reset vector also provides a starting address which is different from that provided by a reset circuit. 26. What are the different categories of embedded operating system? Operating system used in embedded system can be broadly divided into the following categories Non-real-time embedded operating system Real-time operating system Mobile/handheld operating system 27. List the different categories of OS. Single-tasking OS (MS-DOS) Multi-tasking OS (WINSOWS XP) Single-user OS (MS-DOS) Multi-user OS (UNIX) Command-driven OS (MS-DOS) GUI-based OS (WINDOWS XP) 28. List the functions of OS. Task management Memory management I/O management Providing service to applications Providing proper user interface that hides underlying hardware

9 Embedded Systems-QB 29. What is Kernel? Kernel is a program with functions for memory allocation and deallocation, task scheduling, inter process communication, effective management of shared memory access by using the signals, exception handling signals, Semaphores, queues, mailboxes etc. 30. Define RTOS. Real Time Operating System is software for real-time programming, scheduling of tasks, management of resources like memory, devices, etc. to meet time deadlines in embedded systems. 31. List the special requirements in RTOS for embedded systems. Reliability Multi-tasking with time constraints Interrupt Latency control Small footprint Support diskless systems Portability Scalability Support for standard API 32. What is ROM image? The final stage software is also called ROM image, because just as an image is a unique sequence and arrangement of pixels, embedded software is also a unique placement and arrangement of bytes for instructions and data. 33. What are the steps required for converting assembly language into a ROM image? Assembler Linker Loader Locator & Device Programmer

10 34. What is the use of code optimizer? Code optimizer is used in the conversion of high level language into a ROM image for optimizing the code before linking. 35. What is Compiler? Compiler is a software tool that converts a high level program (written using programming languages like C, C++, Java, and so on) into an object code. 36. What is Assembler? Assembler is a software tool that converts an assembly program (written using mnemonics of a processor, i.e., instruction set of a specific processor) into an object code. 37. What is meant by context switching? The mechanism of storing the current status of CPU registers in a stack to run other task is known as context switching. 38. What is meant by Inter-task communication? Tasks may need to exchange data among themselves to synchronize the tasks in an application. This is known as Inter-task communication. The techniques used for ITC are Signals, Semaphores, Mailboxes, Queues, Pipes and Event flags. 39. What is meant by cross platform development? The process of developing machine codes for a specific processor of an embedded system from a high level / assembly level program written on a PC (with different processor) using various software tools is called cross platform development. 40. List the various hardware development / testing tools. Digital Multimeter : Measures current, voltage, continuity of connections Logic Analyzer : Checks the timing of the signals Oscilloscope : Analyze the waveforms in time domain Spectrum Analyzer : Analyze the waveforms in frequency domain 41. List the various software development / testing tools. OS Development Suite Cross-platform Development tools (IDE) ROM Emulator EPROM Programmer Instruction Set Simulator (ISS) In-Circuit Emulator (ICE) 42. List the possible boot sequences of an embedded system. Execute from ROM using RAM for data Execute from RAM after loading the image from RAM Execute from RAM after downloading from the host

11 43. What is meant by Debug port? Debugging a processor based board is very difficult. Hence, manufacturers provide a standardized interface for debugging. JTAG (Joint Test Access Group) port is a mechanism provided to debug the embedded system hardware and also for downloading the software onto the embedded system board. 44. List out the layers of TCP/IP protocol suite. The TCP/IP protocol suit consist of 5 layer Application layer Transport layer Internet protocol (IP) layer Data link layer(referred also as network layer) Physical layer

12 UNIT II PROGRAMMING FOR EMBEDDED SYSTEMS 1. What are advantages of writing embedded software in Assembly Language? It gives a precise control of the processor internal devices. The machine codes are compact. Device driver codes may need only a few assembly instructions 2. What are advantages of writing embedded software in C Language? The development cycle is short for complex systems. Type checking makes the program less prone to error. Control Structures make the program-flow path design tasks simple. Portability. 3. What is embedded C++? Embedded C++ is a version of C++ that provides for a selective disabling which is the disadvantage in C++. So, there is a less run-time overhead and less run-time library. 4. How can optimization be used to eliminate the disadvantages in embedded C++ programs? Optimization can be used as follows. Declare private as many classes as possible. Use of char, int and boolean in place of the objects as arguments Use local variables as much as feasible. Recover memory already used by changing the reference to an object to NULL. 5. What is the use of type checking? Type checking makes the program less prone to error. For e.g. It does not allow subtraction, multiplication and division on the char data types. 6. Define Configuration files. Configuration files are the files for the configuration of the system. Device configuration codes can be put in a file of basic variables and included when needed. 7. What is difference between function and macro-function? A macro function is a collection of codes that is defined in a program by a name. It differs from a function in the sense that once a macro is defined by a name, the compiler puts the corresponding codes for it at every place where that macro name appears. But the codes for a function are compiled once only. 8. What is recursive and reentrant function? Recursive Function: It is a function that calls itself. It must be a reentrant function also. Most often its use is avoided in embedded systems due to memory constraints. Reentrant Function: It is a function that is usable by the several tasks and routines at the same time. All its argument values are retrievable from the stack.

13 9. What is the use of modifier register? When a modifier register is inside a function block, a CPU register is temporarily allocated when needed. There is no ROM or RAM allocation. 10. Define Queue. It is a data structure into which elements can be sequentially inserted and retrieved in a FIFO mode. It needs two pointers, one for the queue tail for insertion and other for the queue head for deletion. 11. Define Stack. A stack is a data structure in which elements can be pushed in or pulled out. It works on the principle of Last-In-First-Out (LIFO). 12. How interrupts are handled in Queue? Queuing of pointers to the function on interrupts and later on calling the functions from this queue is a better approach as it provides the use of short execution time interrupt-service routines. 13. Explain briefly stack overhead. The repeated call to recursive function may cause the stack to full. This leads to insufficient memory. Hence the stack overhead may occur which is primarily due to overflow of the stack. 14. What is meant by inline assembly? Inserting the assembly language codes in between the high-level language codes are called inline assembly. It gives the benefits of processor specific instructions and addressing modes. 15. What is Optimization of memory? When codes are made compact and fitted in small memory without affecting the code performance, it is called memory optimization. 16. Define scalar data types? The character, integer, unsigned integer, floating point number, long and double are called scalar data types. Unlike an array data consists of one single element. 17. Give some examples for reference data types. Arrays and strings are examples of reference data types. 18. What is meant by platform independence? A code that can port on different machine and different operating systems is said to be platform independent code. 19. What are preprocessor directives? It is the program statements and directives for the compiler before the main function to define global variable, global macro, new data type and global constants.

14 20. What are the differences between including a header file and a text file or data file? The differences between including a header file and a text file or data file are, The header files are well tested and debugged modules. They provide access to standard libraries. The header file can include several text file or C files. A text file is description of the text that contains specific information. 21. List the Integer data types available in C programming language. Data type Size Range unsigned Char Short int Int Long int 8 bits 16 bits 16/32 bits 32 bits 0 to to 65,535 same as unsigned short / long int 0 to 4,294,967,295 signed Char Short int Int Long int 8 bits 16 bits 16/32 bits 32 bits -128 to to same as unsigned short / long int -2,147,483,648 to +2,147,483, Why TYPEDEFS are used in embedded system programming? C s primitive data type char may default to either signed or unsigned, and its primitive data type int may have size of 16 or 32 bits. In most of the embedded applications, it s imperative to know the number of bits and range of most variables. Hence, to avoid C s ambiguity, derived data types are formed using TYPEDEFS and placed in a text file (Eg. typedefs.h) and included in every source code file that uses them. 23. What are the two types of data conversions? PROMOTION: A conversion is called a promotion, when there is no potential loss of accuracy as when assigning an integer value to a floating point variable. DEMOTION: It is the conversion which causes a loss of accuracy, when a floating point variable is assigned to an integer variable, or when a 32-bit integer value is assigned to a 8- bit char. Demotion usually make the compiler to issue a warning. 24. List the Boolean and Bitwise operators. Operation AND OR XOR NOT Boolean Operator && (Not supported)! Bitwise Operator & ^ ~

15 25. Find the result of the following expression? a) Boolean: (5!3) && 6 Ans:= = = = = (True OR (NOT True)) AND True (True OR False) AND True (True) AND True True 1 b) Bitwise: (5!3) & 6 Ans:= = = = = List the bitwise operations performed on data bits. Testing bits Setting bits Clearing bits Inverting bits Extracting bits Inserting bits ( OR!( )) AND ( OR ) AND ( ) AND What is the significance of Pointers in C programming? A Pointer in C is a variable that contains an address of a variable. This helps to access the data of a variable faster in memory and in particular for array types of data. Eg. Int A, *B, C ; A & C are normal variable and B is a Pointer variable A = 10 ; Variable A is assigned with a value, 10 B = &A ; Variable B is assigned the address of variable A C = *B ; Variable C is now assigned the content at address stored in variable B 28. What is an Array? An Array is an aggregate data type composed of several members of same data type. The consecutive locations in memory are allocated for an array. The starting address of the array (i.e., a[0]) is called Base address. Eg. Int a[5]; a[0] a[1] a[2] a[3] a[4]

16 29. Explain about manipulating bits in memory. Embedded Systems-QB 30. How testing a bit is made? 31. How setting a bit is made?

17 32. How clearing of a bit is made? Embedded Systems-QB 33. How inverting a bit is made? 34. How to extracting of a bit is made? 35. How to replacing of a bit is made?

18 36. What is a structure? A Structure is a aggregate data type composed of several distinct members. A single structure variable can contain member elements that represent a mix of chars, ints, doubles, etc. Structure declaration in C program Structure variable declaration struct PERSON { Int age; Char gender; }; struct PERSON sue; (or) PERSON sue; Initialization of structure variable members sue.age = 25; sue.gender = F ; (or) PERSON sue = {25, F }; 37. What is meant by packed structures? Structures are always stored in memory with their member components in the same order as they appear in the structure description and there is no requirement that the components be contiguous. Struct {char c; Int I;} x; padding padding padding x.c x.i Sometimes, we need to use structures to describe a layout in which all the data is contiguous. Thus, packed structures are a layout of data in memory in which the padding of zeros is disabled. Struct {char c; Int I; } x attribute ((packed)); x.i x.c

19 38. What are Bit fields? Embedded Systems-QB Bit fields in structures allow us to access the data using cleaner syntax that hides all the necessary bit manipulation. Illustration of declaring structure bit fields Describing of time as structure in which the hours, minutes and seconds are declared as structure bit fields. typedef struct { WORD16 seconds : 6, minutes : 5, hours : 5; } TIME time1; Time of 13:34:18 can be initialized into the packed representation time1 using simple reference operator as follows, time1.hours = 13; time1.minutes = 34; time1.seconds = 18/2; 39. What is a Union? Union is an aggregate data type in which the members of it share a common memory space. typedef union { unsigned long int FIXED32PARTS part; } FIXED32REAL result; real; result.part.whole result.part.fract result.real Explain the process of Assembler. The translation of assembly-language source code into binary object code is a two-step process in assembler. The assembler makes two complete passes over the source code of the program. During the first pass; the assembler builds a symbol table that contains the information about programmer defined identifiers, such as the labels attached to instructions and the names of variables stored in memory. Duringthesecondpass; the assembler uses this information to construct the representation of the individual instructions.

20 41. List the instructions in C that transfers the program control to another part of memory. In C language, unconditional jumps are created by break, continue, switch and goto statements and at the end of loops. 42. Explain the importance of String instructions. There are some common loop operations that can be implemented using the Intel string instructions for ultimate speed. For example, string instructions can be used to initialize a region of memory to a constant value, scan a region of memory for a particular value, copy one region of memory to another, or compare the contents of two regions of memory. 43. List the Intel conditional JUMP instructions. For comparing unsigned operands JA/JNBE - Jump if above / jump if not below or equal JAE/JNB - Jump if above or equal / jump if not below JBE/JNA - Jump if below or equal / jump if not above JB/JNAE - Jump if below / jump if not above or equal For comparing signed operands JG/JNLE - Jump if Greater / jump if not less or equal JGE/JNL - Jump if Greater or equal / jump if not less JLE/JNG - Jump if less or equal / jump if not greater JL/JNGE - Jump if less / jump if not greater or equal For equality comparisons JE/JZ - Jump if equal / jump if zero (ZF=1) JNE/JNZ - Jump if not equal / jump if not zero (ZF=0) Other JUMP instructions JC - Jump if CF=1 JNC - Jump if CF=0 JS - Jump if SF=1 JNS - Jump if SF=0

21 44. List the attributes of Objects stored in memory. Type Name Value - char, int, unsigned int, etc. - The identifier used to access the object - The data held within the object Address- The address in memory where the object resides Scope - That part of the source code where the object s name is recognized Lifetime- The notion of when the object is created and destroyed, and thus, when it is available for use. 45. What is meant by scope in memory management? Scope of a variable is based on the place of declaration in the program. It is either declared (1) outside of all functions to create global variables or (2) immediately following a function header to create temporary variables local to the function. 46. List the types of Memory allocation available in C. Method Object is created Object is initialized Object is destroyed Automatic Each time the program enters the function in which it is declared If specified in the declaration, initialization occurs each time the program enters the block Each time the function returns Static Once: When the program is first loaded into the memory Once: Just before the program starts to run Once: When the program stops Dynamic By calling the library function malloc() By writing executable statements that modify its content By calling the library function free() 47. What is meant by shared memory? When two or more asynchronous (no predictable time relationship) instruction sequences access the same data, that data is called shared memory. Access to shared memory must be carefully coordinated or else data corruption may occur.

22 48. What is meant by shared functions? A shared function in one that is called by more than one thread; any function called by a shared function is also a shared function. Any static object referenced within a shared function is thus form of shared memory. Since there is only a single instance of the object, its content is inherently shared by all threads that call a function that references it. 49. Explain the type qualifier const. The keyword const is used to declare so that an object s value may not be modified by the program, i.e., that its value is read only. The declaration of a const object must include an initial value, since no subsequent attempt to set its valued is allowed. 50. Explain the type qualifier Volatile. The keyword volatile may be attached as qualifier on the declaration of an object in C to indicate that its value may be asynchronously modified by mechanism other than the code in which the declaration appears, such as DMA or ISR. 51. What is meant by Life Time of a variable? 52. What is Fragmentation?

23 UNIT III HARDWARE PLATFORM Embedded Systems-QB 1. In what way is PIC microcontroller different from 8051? Most PIC microcontrollers are RISC based processors with Harvard architecture, where as 8051 is based on Von-Neuman architecture. Harvard architecture makes use of separate program and data memories. PIC microcontroller has different data size for program and data memory and hence it is difficult to use external memory for PIC microcontroller. 2. List the features of PIC 16C6x/7x. PIC microcontroller is designed in Harvard Architecture Separate memory for program and data Program memory: has 13-bit address & 14-bit data bus Data memory: has 8-bit address & 8-bit data bus 13-bit program counter Pipelined architecture for fast execution speed Has inbuilt ADC and Watch-dog timer 3. Compare features of other PIC microcontrollers.

24 4. Draw the pin diagram of 16C61 and 16C71 microcontroller. 5. Describe the status register (Flag Reg) of PIC16C6X microcontroller. STATUS register contains various flags and register bank select bits: D 7 D 6 D 5 D 4 D 3 D 2 D 1 D RPO TO PD Z DC C RPO TO PD Z DC C Register bank select (to select 2 banks; one bit RPO is sufficient) Time-Out Bit (Reset status bit, is only readable) Power-Down Bit (Reset status bit, is only readable) Zero bit Digital-carry / Borrow bit Carry / Borrow bit 6. State the power consumption of PIC microcontroller.

25 7. What is meant by instruction pipelining? Embedded Systems-QB PIC16C6x/7x family of microcontrollers use Harvard Architecture and instruction pipelining to achieve exceptionally fast execution speed for a given clock rate. Through pipelining, instruction fetch and execution are carried out simultaneously in a single cycle. 8. List the CPU registers of 16Cxx family microcontrollers. 9. What is PCL and PCLATH register? PC, the program counter of PIC microcontroller is 13-bits wide and PCL is the lower byte of the PC. PCLATH, stand for PC Latch and it holds the upper 5-bits of the program counter. PCLATH is transferred into the PC when content is written into PCL.

26 10. List the SFRs of PIC microcontroller. Embedded Systems-QB The lower bytes of register bank are identified as Special Function Register (SFRs). The CPU and peripheral modules use SFRs for controlling the operation of the device. 11. Describe the Register file structure in PIC microcontroller. The term Register File is PIC terminology used to denote the locations that an instruction can access via an address. The register file consists of two components. 1. General purpose register file 2. Special purpose register file

27 The general purpose register file is another name given to RAM memory of PIC microcontroller. The special purpose register file contains input and output ports as well as the control registers used to establish each bit of a port as either an input or an output. The register file structure is illustrated in figure below with addresses that span the 8-bit range from 00 to FF. Because the direct addressing mode employed by many instructions use only 7-bit of the instruction to identify a register file address, the 8th bit of the register file address must come from a separate register bank selection bit, RP List and brief the addressing modes in PIC microcontroller. Direct Addressing: It uses 7 bits of instruction and the 8thbit from RP0. If RP0 bit is 0; then bank 0 is selected or otherwise bank 1 is selected. Indirect addressing: In this mode; the 8-bit address of the location in register file to be accessed is written in FSR and INDF register is used for indirect addressing. 13. What is FSR? FSR stands for File Selection Register. FSR is the pointer used for indirect memory addressing in the whole register file. It must be noted that, in PIC, every instruction that can be used for direct addressing may also be used in a different way for indirect addressing. The only difference in indirect addressing mode is that one has to write the address byte in FSR and then use INDF in the instruction. Thus, FSR points to the desired memory location. 14. List the reset action that takes place in PIC microcontroller. PIC reset action takes place due to difference mechanism. Those are Power on reset (POR), MCLR reset during the normal operation, Master clear MCLR reset during SLEEP mode, Watch dog timer reset during normal operation, Brown out reset (BOR). 15. Explain the brown-out reset feature of PIC microcontroller. PIC microcontroller can be reset automatically in running condition, due to the brown-out. Brown-out reset takes place when the supply voltage falls below 4V. The device remains in brown-out reset condition until the supply voltage is restored. PIC 16C61 and 16C71 does not support this feature.

28 16. Explain the structure of Watchdog timer in PIC microcontroller. Embedded Systems-QB Watch-dog timer is a simple timer circuit that prevents the processor from endless loop (hanging condition) and looks after the functioning of the system with respect to time. The watch-dog timer will reset the PIC microcontroller when the CLRDWT instruction is not executed periodically. CLRDWT instruction resets the TO bit in the status register. WDT timer can also be reset the TO bit, when the CLRDWT is not executed periodically. The normal time-out period of PIC microcontroller is around 18ms. The watch-dog timer is enabled at the time of device programming and it cannot be turned off after programming. 17. Explain about Clock generation in PIC briefly.

29 Alternate method of generating clock signal is by connecting quartz crystal to the PIC microcontroller along with two start-up capacitors. 18. Short notes on I/O ports of PIC microcontroller Port A: RA0 to RA4 (5 lines) (Address 05). RA4 has alternate function. TRISA (85H) is SFR used to configure these lines individually as either inputs or outputs. Setting bit in TRIS will configure as input and 0 will configure as output. Port B: RB0 to RB7 (8 lines). TRISB It has weak internal pull up which is to be enabled. POR disables pull-ups. 19. Explain about the interrupts in PIC There are 3 Interrupt Sources for PIC16C6X. External Interrupt: Due to external source. Edge Sensitive RB0/INT causes this interrupt. This interrupt wakes up processor from SLEEP. This must be set before going into SLEEP mode. Timer 0: Timer 0 overflows when timer count overflows from FF to 00. Port B Change Interrupt: A change from high to low or low to high on port B pins RB4 to RB7 causes this interrupt. This interrupt can wake device from SLEEP. 20. Write short notes on Timers in PIC16C6X. All PIC16C6X devices have three timer modules except for the PIC16C61, which has one timer module. The Timer0 module is a simple 8-bit overflow counter. The clock source can be either the internal system clock (Fosc/4) or an external clock. When the clock source is an external clock, the Timer0 module can be selected to increment on either the rising or falling edge.

30 21. List out the types of instructions in PIC Microcontroller. Embedded Systems-QB Each PIC16CXX instruction is a 14-bit word divided into an OPCODE which specifies the instruction type and one or more operands which further specify the operation of the instruction. Byte-oriented, Bit-oriented, Literal and control operations 22. Explain Byte-oriented instruction set. Byte-oriented instructions, 'f' represents a file register designator and d represents a destination designator. The file register designator specifies which file register is to be used by the instruction. The destination designator specifies where the result of the operation is to be placed. If d is zero, the result is placed in the W register. If d is one, the result is placed in the file register specified in the instruction. 23. Explain Bit-oriented instruction set. Bit-oriented instructions, 'b' represents a bit field designator which selects the number of the bit affected by the operation, while 'f' represents the number of the file in which the bit is located. 24. Short note on literal and control operation instruction set. Literal and control operations, 'k' represents an eight or eleven bit constant or literal value.

31 25. Write short notes on INTCON register of PIC16C6x/7x controller. Embedded Systems-QB INTCON is an Interrupt control register in PIC microcontrollers for controlling all interrupts.

32 26. List the external interrupts & timers of PIC microcontroller. The PIC microcontroller has one pin RB0/INT, which serves as its primary external interrupt input. In addition to above, it has three timers TIMER0 TIMER1 & TIMER2 with CCP module. 27. List the features of ADC in PIC 16C6x/7x microcontroller. PIC 16C7X supports analog inputs. PIC 16C71 microcontroller has four analog channels of 8- bit ADC, with 20 µs of conversion time per channel. Four analog channels AIN0, AIN1, AIN2 and AIN3 are the alternate functions of Port_A pins RA0, RA1, RA2, and RA3 respectively. ADCON0 controls the function of pins RA0 to RA3. This allows the configuring pins RA0-RA3 as analog or digital inputs. 28. What is sleep mode in PIC microcontroller? PIC microcontroller supports a power saving Sleep mode. The clock may be frozen with all the data preserved in the processor memory. A software command allows the processor to enter into this mode. It will be in sleep mode until the PIC is reset again.

33 Embedded Systems-QB 30. Explain the operation of OPTION register.

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35 UNIT IV REAL TIME OPERATING SYSTEMS CONCEPTS Embedded Systems-QB 1. Define RTOS. It is an operating System for embedded system with real time task scheduling, interruptlatency control, synchronization of tasks with IPCs and predictable timing behavior of the system. 2. Name some RTOS services. (i) Basic OS functions (ii) RTOS Main functions (Task Scheduling & interrupt latency control) (iii) Time Management (iv) Predictability 3. Compare OS and RTOS. OS: On a PC, OS takes control of the PC as soon as it is turned on and then it lets the application program to start. OS checks any pointer which passes into a system function for its validity. OS consumes lot of memory space and it contains all in-built functions. RTOS: Application program is linked to the RTOS. At boot-up, application usually gets control first and then it starts RTOS. Many RTOS don not protect themselves and skip the checking process for better performance. To save memory, RTOS has only the functions needed for an application. 4. What is Round Robin or cyclic scheduling? It is a scheduling algorithm in which the tasks are scheduled in sequence from a list of ready tasks. 5. Explain briefly about Preemptive scheduling. A scheduling algorithm in which a higher priority task is forced (Preempted) to block the low priority task by the scheduler. 6. What is Time Slicing and Fixed real time scheduling? Time Slicing Scheduling It is a scheduling algorithm in which each task is allotted a time slice after which it is blocked and waits for its turn on the next cycle. Fixed Real Time Scheduling It is a scheduling strategy in which the time for each task is fixed. 7. Explain briefly the term Task. Task is a subroutine in an application that makes certain action to be performed. A Task that has its independent program counter values and an independent stack. A single CPU system runs one task at a time.

36 8. What is Task State? A state of a task changes on scheduler directions. A task at an instance can be in one of the four states, idle, ready, blocked ad running that are controlled by the scheduler. 9. Explain Task scheduler. It is part of a RTOS. It keeps track of the state of each task and decides which one task should go into the running state. Scheduler in an RTOS looks at the priorities assigned to tasks, and among the tasks that not in the blocked state, the one with highest priority is allowed to run and the rest of them are made to wait in the ready state. 10. When a blocked task is allowed to run on a processor? When a task is blocked, it never gets the processor. Therefore, an interrupt routine or some another task in the system should signal that whatever the blocked task waiting for has happened. Otherwise, the task will be blocked forever. 11. How does a scheduler know whether a task is blocked or not? RTOS provides a collection of functions that tasks can tell a scheduler what events they wait for and to signal that events have happened. 12. What happens if all the tasks are blocked? If all the tasks are blocked, then the scheduler will spin in some tight loop somewhere inside the RTOS, waiting for something to happen. If nothing ever happens, then it ends in an infinite loop. Therefore care must be taken by programmer to invoke a interrupt routine that call some RTOS function that unblocks a task. 13. What if two tasks with the same priority are ready? There are two options in this situation. (1) RTOS should declare as illegal when two tasks are assigned with same priority. (2) RTOS can time-slice between two tasks that has the same priority. 14. List the rules to decide if a function is Re-entrant. 1. A reentrant function may not use variables in a non-atomic way unless they are stored on the stack of the task that call the function or are otherwise the private variables of that task. 2. A reentrant function may not call any other functions that are not themselves reentrant. 3. A reentrant function may not use the hardware in a non-atomic way. 15. Define Inter process communication (IPC). An output from one task (or process) passed to another task through the scheduler and use of signals, exceptions, semaphores, queues, mailboxes, pipes, sockets, and remote procedure call is known as inter process communication.

37 16. Define Semaphore. Semaphore is a special variable or function that is used to take note of certain actions to prevent another task or process from proceeding. 17. List the semaphore related problems. Forgetting to take the semaphore Forgetting to release the semaphore Taking the wrong semaphore Holding a semaphore too long 18. Explain Mutex, Counting and Resource Semaphore. Mutex Semaphore A special variable used to take note of certain actions to prevent any task or process from proceeding further and at the same time let another task exclusively proceed further. Counting Semaphore Sometimes, a semaphore can be taken multiple times. A semaphore can be an integer which can be incremented when released and decremented when taken. If a task tries to take a semaphore when the integer value is equal to 0, then the task will be blocked. This is called Counting semaphore. Resource Semaphore Sometimes RTOS allows a semaphore to be released only by the task that has taken them. These semaphores are useful for shared data problem, but cannot be used for communication between two tasks. Such semaphores are called as Resource semaphores. 19. What are the problems that may arise while using semaphores? The problems that may while using semaphores are, Sharing of two semaphores creates a deadlock problem. Without a timeout an ISR worst-case latency may exceed the deadline. If a semaphore is not taken, and another task uses a shared variable. When using multiple semaphores, if an unintended task takes the semaphore, it creates a problem. It may introduce priority inversion problem. 20. What is shared data problem? If a variable is used in two different tasks and another task if interrupts without before the operation on that variable is completed, then the shared data problem arises. 21. List the ways to protect the shared data. Disabling the interrupts Taking semaphores Disabling the task switches

38 22. Explain briefly Deadly embrace situation. Embedded Systems-QB Consider a situation in which two tasks (task1 and task2) are using two semaphores, semaphore_a and semaphore_b. When task1 is run, it takes semaphore_a and before it proceeds further and takes semaphore_b, RTOS switches to task2. Now task2 takes semaphore_b and it waits for release of semaphore_a by task1. None of these tasks are able to proceed further. This situation is called Deadly embrace. 23. What is priority inversion problem? How it can be solved? A problem in which a low priority task unintentionally do not release the semaphore for a higher priority task. This makes the high priority task to wait for low priority task to release the semaphore. This is called Priority Inversion. This problem can be solved by temporarily boosting the low priority task to higher priority task which is called as priority inheritance. 24. Explain the term (i) Message Queue (ii) Mailbox (iii) Pipe (iv) Socket. Message Queue RTOS allows a task to send multiple messages into a FIFO queue for use by another task(s) using queue message as an input. Mailbox RTOS allows a certain no. of messages to be stored in each mailbox. Separate functions are used to identify the appropriate mailbox, to add and read a message from the selected mailbox. Pipe Pipes are like queues. RTOS can create them, write to them, read from them and so on. Socket It provides the logical link using a protocol between the tasks in a client-server or peer-topeer environment.

39 25. List the pitfalls in using Mailbox, Message queues and Pipes. Embedded Systems-QB Most of the RTOS do not restrict which tasks can read from or write to any given queue, mailbox or pipe. Therefore, programmer must ensure that tasks use the correct one each time. RTOS cannot ensure that data written onto a queue, mailbox or a pipe will be properly interpreted by the tasks that read it. Running out of space in queues, mailboxes or pipes is usually a disaster for embedded software. Passing pointers from one task to another through a queue, mailbox or pipe is one of the several ways to create shared data inadvertently. 26. What is Timer and counting devices? A Timer gets the inputs from the internal clock of a processor or from system clock and generates a required time delay. Counting device is a unit for getting the count-inputs on the occurrence of events that may be at irregular intervals. 27. What are the types of Timer? There are two types of timer. They are, Hardware timer Software timer 28. What is Timer Overflow or Time-Out? A state in which the number of count inputs exceeded the last acquirable value and on reaching that state, an interrupt can be generated. This state is called Time-Out or Timer Overflow. 29. What is the difference between hardware timer and software timer? Hardware timer gets the inputs from the internal clock with the processor or system clock. A device driver program programs it like any other physical device. Software timer executes a program which increases or decreases a count variable on an interrupt from a timer output or from a real-time clock interrupt. 30. What are the different states in a timer? The different states in a timer are, Reset State Idle State Present State Overflow State Active or Blocked State Done State

40 31. Is it necessary to have a hardware timer device in a system? How does it work? Yes, it is necessary to have atleast one hardware timer device in a system. It is used as a system clock. The hardware timer gets the input from a clock out signal from the processor and activates the system clock as per the num ticks preset at the hardware timer. 32. What is an Event? An event is essentially a Boolean flag that tasks can set or reset and that other tasks can wait for. Event invokes a interrupt routine that runs a waiting task. 33. Compare Semaphores, Events and Queues/Mailbox/Pipe. Semaphores are usually the fastest and simplest methods. However, not much information can be passed through a semaphore, which passes just a 1-bit message saying that it has been released. Events are a little more complicated than semaphores and take little more of processor time. The advantage of events over semaphores is that a task can wait for any one of the several events at the same time and it can wait for only one semaphore. Queues (also mailboxes & pipes) allow sending a lot of information from one task to another. The drawback of queues (also mailboxes and pipes) is that adding and reading a message is more processor intensive and more prone to insert bugs while programming them. 34. How a block of data is passed using queue? Passing a pointer to a buffer from one task to another through a queue is a common way to pass a block of data. 35. Explain the problem in using malloc() and free() functions for memory management in RT embedded systems. In real time embedded systems, malloc() and free() are avoided because of their slow response and unpredictable execution times. Instead, most of the RTOS offer fast and predictable functions along with free fixed size buffers. 36. List the two rules that an interrupt routine must follow in RTOS environment that do not apply to task codes. Rule-1: An interrupt routine must not call any RTOS function that might block the caller. Rule-2: An interrupt routine may not call any RTOS function that might cause the RTOS to switch tasks unless the RTOS knows that an interrupt routine, and not a task is executing.