Real Time Embedded Systems. Lecture 5 January 24, 2012 Embedded C Programming

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Rudolf Lindsey
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1 Embedded C

2 Real Time Embedded Systems Lecture 5 January 24, 2012 Embedded C Programming

3 Section Topic Where in the books Catsoulis chapter/page Simon chapter/page Zilog UM197 (ZNEO Z16F Series Flash Microcontroller Contest Kit User Manual) Zilog UM171 (ZiLOG Developer Studio II ZNEO User Manual) Zilog PS220 (ZNEO Z16F Series Product Specification) Zilog UM188 (ZNEO CPU Core User Manual) Assorted datasheets

4 Embedded Programming Whats special/different about programming embedded systems? Low level Performance concerns Robustness Tool chain Debugging, Test No OS, or limited OS Limited libraries Limited choice of languages

5 Embedded Software Development Process C file Cross Compiler Assembly file Assemble r Debugger Target Device Binary file Binary file Emulator Library Linker Executable file Programmer IDE

6 Style Lots of style guides. Pick one. No need to invent your own. Style guides often include project management style. Use this one

7 Style Variable and function names should be sufficient to understand the meaning. count, temp, time for example i,j,k are acceptable for index variables x,y,z are acceptable for coordinates Function names should take the place of verbs in the programming language

8 Tabs vs Spaces Religious arguments I like spaces, 4 for each level of indent Others argue for tabs, set for 8 characters, less file space needed Other argue for 2 spaces, more room and less spaces wasted.

9 Where to put the curly bracket Some argue on the line after the function static void function(int n) { // } Others (like me) argue for the same line: static void function(int n) { // } Learn to live with both.

10 No Other Options Stuff like this is not good style: while (PEIN&SCIO) { wait-- ; if(wait==0) { ferror(); } }

11 Always use {} Even when you don't absolutely need to. In all loops and all if/then/else if (sp>0) return val[sp] else printf( error\n ); return 0.0; if (sp>0) { return val[sp] } else { printf( error\n ); return 0.0; }

12 Makes for faster/easier fixes if (sp>0) sp += 2; return val[sp] else printf( error\n ); return 0.0; if (sp>0) { sp += 2; return val[sp] } else { printf( error\n ); return 0.0; }

13 Comments Comment the module Description, Implementation, Requirements Comment the functions Describe the function, parameters, exceptional conditions Comments the constants and globals Describe the global and who uses it Comment anything that needs explanation Particularly helpful with specific hardware requirements

14 Comments Fanciness does not help /***************************************** * * * This type of comment header is * * a royal pain to maintain, so they * * tend to be inaccurate * * * *****************************************/ /***************************************** There is nothing wrong with this and its just as easy to read and even easier to maintain *****************************************/

15 Modules/APIs Minimize coupling, dependency Use.h and.c files appropriately Naming Module LED.c, LED.h Function LED_init() LED_clear() Constants LED_BUFFER_MAX Include profuse documentation

16 .c &.h.h.c Stuff that's public like externs declarations, function prototypes and public #defines Stuff that's private (this c source file only)

17 Prevent multiple includes Some compilers support #pragma once Others don't (like the ZDS II IDE) Use a #include guard like this #ifndef _MODULE_H_ #define _MODULE_H_ //prototypes and stuff goes here #endif /* _MODULE_H_ */

18 Style You can follow one of the many style guides (like K&R) or Keep your program clear, easy to read. No bonus points for terse, confusing, most code per page, least number of comments.

19 Unless you can do stuff like this... int X=320,Y=200, n=0,m, x,y, j=1024; double T=44.0 /7,P[ ],C[5] ={ 0,3, 0,0,8},p=1, B=11.0 /630, f=0,r = 3,g =7,b =13,*q=P, D,*J; unsigned char U[66666],*v=U,*h,l[5555],c=0,*e,*a,*z; #include <math.h> #define R1(t) t=(int)(t\ * )%j; t/=j; #define Rl(C,t)\ n++[c] = t*n/12; #define RI(C) B=-B; R1\ (r)r1(g )R1(b )for(n\ =0; n<j; ){ Rl(C,r)Rl\ (C,g)Rl(C,b)++n; }

20 A Bad Example Actual Example code from a MicroChip datasheet //... void sak(void) // SAK = 0-1 { unsigned char wait=timeout ; // init "wait" variable P3DIR = 0x5a ; // P3.0 = INPUT while (P3IN&SCIO) // if SCIO = 1 { wait-- ; // decrement timeout variable if(wait==0){ferror() ;} } // if timeout, final error dlthb() ; dlthb() ; // wait a bit period if(!(p3in&scio)) // no edge inside SAK { ferror() ; } // same error inside SAK else { P3OUT = SCIO ; // set P3.0 P3DIR=0x5b ; } } // if no_error, P3.0=OUTPUT

21 Made Better //... void sak(void) { unsigned char wait=timeout; // Set P3.0 to INPUT P3DIR = 0x5a; while (P3IN&SCIO) { wait-- ; if(wait==0) { ferror() ; } } // wait a bit period dlthb() ; dlthb() ; } // no edge inside SAK if (!(P3IN&SCIO)) { ferror() ; } else { // set P3.0 P3OUT = SCIO ; P3DIR=0x5b ; }

22 Zilog/Z16 Specifics Data sizes Memory Model Call Frames Static vs Dynamic Frames Keywords Compiler settings Standard Libraries

23 Z16 Data Size We know that the exact data size in C is not specified. Current C compilers provide fairly consistent data sizes. The Z16 compiler is consistent char 1 byte short 2 bytes int 4 bytes long 4 bytes float 4 bytes double 8 bytes

25 Z16 Memory Architecture The Z16 has multiple blocks of memory Flash SRAM SFR External (add on)

26 Z16 Memory Map SFR External Memory Internal SRAM FF_FFFFH <- Top of IO memory FF_E000H <- Bottom of IO memory FF_C000H FF_E000H FF_BFFFH <- Top of RAM FF_xxxxH <- Bottom of RAM FF_8000H External Memory Internal FLASH Flash option bits 00_xxxxH <- Top of non-volatile 00_7FFFH 00_0xxxH 00_0000H <- Bottom of memory

27 Z16 Memory Map SFR External Memory Internal SRAM FF_FFFFH <- Top of IO memory FF_E000H <- Bottom of IO memory FF_C000H FF_E000H FF_BFFFH <- Top of RAM FF_xxxxH <- Bottom of RAM External Memory FF_8000H Device Specific Boundary Internal FLASH Flash option bits 00_xxxxH <- Top of non-volatile 00_7FFFH 00_0xxxH 00_0000H <- Bottom of memory

28 Z16 Memory Map SFR External Memory Internal SRAM External Memory Internal FLASH Flash option bits FF_FFFFH FF_E000H FF_C000H FF_E000H FF_BFFFH FF_xxxxH FF_8000H 00_xxxxH 00_7FFFH 00_0xxxH 00_0000H _Near 16 bit addressable RAM space _Far 32 bit addressable RAM space _Erom 32 bit addressable ROM space _Rom 16 bit addressable ROM space

29 Memory Access _Near Specifies that data be placed RAM in address space (16-bit address) _Far Specifies that data be placed in external RAM address space (32-bit address) _Rom Specifies that data be placed in ROM (FLASH) address space (16 or 32 but address) _Erom Specifies that data be placed in internal or external ROM (32 bit address) space

30 Settings in ZDS II

31 Memory Models The Z16 IDE supports 2 memory models: small and large. They differ in where data is placed. Choice of model size does not effect the program size much, just the space for data (and also the size of the address needed to access the data).

32 Small Memory Model Small Globals stored in RAM address space (_Near). Locals and function parameters are stored on the stack, also in RAM (_Near) space. All using 16- bit addresses. Globals can be stored in _Far, _Rom, _Erom using the a placement specifier Locals are always in RAM (_Near) and specifiers are ignored.

33 Large Memory Model Large - Globals stored in _Far address space. Locals and function parameters stored on the stack, also in _Far space. All using 32-bit addresses. Globals and static variables can be specified with _Near, _Rom, _Erom

34 Data Space near int near_data; // in RAM (16bit address) far int far_data; // in RAM (32bit address) rom int rom_data; // in ROM (in flash)

35 Memory near int List[10]; far int data[200]; rom int factors[] = {9,1,2,7,3,9,2,6}; char *thing; char far *fp; // near if small memory model // far if large memory model // the char is stored in far memory // fp is stored in near ram for small model // fp is stored in far ram for large model char rom * near charptr; // charptr is a pointer to a char in rom // charptr is stored in near ram

36 Endianness Data is stored in ZNEO memory in big endian order. The address of a multi-byte word (2 or 4 bytes) is the most significant byte.

37 Endianess Endian big First byte (lowest address) most significant Last byte (highest address) least significant little least significant most significant

38 Compiler Settings Compiler settings can be changed with #pragma directives. #pragma noopt Disables optimization. A number of ways to disable part of the optimization: nojumpopt, nolocalopt, nooptlink, nopeephole. Can also turn off optimization in IDE

39 Standard Run Time Libraries <assert.h> - Diagnostics <errno.h> - Macros for reporting error conditions <stddef.h> - Standard definitions <ctype.h> - Character handling (isanum() etc) <limits.h> - Min/Max values for various data types (INT_MAX, INT_MIN). <float.h> - Floating point limits. <math.h> - Math functions

40 Standard Run Time Library <setjmp.h> <stdarg.h> <stdio.h> <stdlib.h> <string.h> <stddef.h> - Nonlocal jumps - Variable arguments - printf, scanf, getchar, putchar IO functions - Standard types (errno.h, stddef.h, math.h, string.h). - Functions for manipulating character arrays. - Stardard defines

41 Non-standard Libraries <sio.h> - non-standard IO functions (init_uart, etc) <zneo.h> - Defines for all of the Z16 special function registers.

42 API Example Example Status.c Use the modem lights for program status indicators.

43 /******************************************************************* status.h Status Indicators December 2006 (updated for ZNEO February 2009) Dan Eisenreich Set status.c for documentation *******************************************************************/ #ifndef _STATUS_H_ #define _STATUS_H_ #define STATUS_LED1 0x01 #define STATUS_LED2 0x02 #define STATUS_LED3 0x04 #define STATUS_LED4 0x08 #define STATUS_LED_ALL 0x0F // Get the status LEDs ready to use and clear them all. void status_init(void); // Turn on LEDs void status_set(int num); // Turn off LEDs void status_clear(int num); #endif /* _STATUS_H_ */

44 #include <zneo.h> #include "status.h" /******************************************************************* status.c Status Indicators December 2006 (updated for ZNEO February 2009) Dan Eisenreich Use the 4 MODEM status LEDs on the Z8F6402 demo board as progress indicators. These are easier to use than the LED arrays (no latch) and won't interfere with text being displayed. Needs to have 4 jumper wires put in the modem socket (see below). CONFIGURATION: ============= The LEDs are mapped with wires like this: You need to add these wires v Status 1 -> PF0 -> J2 pin 25 -> wire -> J3 pin 9 -> LED D10 (TX) Status 2 -> PF1 -> J2 pin 32 -> wire -> J3 pin 8 -> LED D9 (DTR Status 3 -> PF2 -> J2 pin 28 -> wire -> J3 pin 7 -> LED D8 (RX) Status 4 -> PF3 -> J2 pin 26 -> wire -> J3 pin 6 -> LED D7 (DCD)

45 If you need more detail, look at the modem socket (connectors J2 and J3) These wires here are the ones that need to be added. J3 J2 ===== v ===== > PF > PF > PF2 D < ---/\/\/\ (-+ 29 D < ---/\/\/\ ( D < ---/\/\/\ ( D < ---/\/\/\ > PF1 V

46 You can hook these LEDs up any way you want, I chose this way so that all 4 LEDs where connected to 4 sequential bits on one IO port (port F). ********************************************************************/ /******************************************************************** status_init Configure the lower half of port F to dive these LEDs */ void status_init(void) { // Port F xxxx0000, x = leave alone, 0 = clear bit PFDD &= ~0x0F; // Set the data direction to OUT PFAF &= ~0x0F; // No alternate function PFOC &= ~0x0F; // No output control PFOUT &= ~0x0F; // Initialize them to all off }

47 /******************************************************************** status_set set (turn on) the status LEDs status_set(0) clears all LEDs status_set(0xf) turns on ALL LEDs */ void status_set(int num) { /* We could set the bits individually but thats more work. So instead we get PFOUT, clear the lower 4 bits, and reset them according to the number provided then send that back out to PFOUT. So setting 0 clears all, setting 0xF sets all. */ PFOUT = (PFOUT & 0xF0) (num & 0x0F); } /******************************************************************** status_clear clear an individual LED status_clear( 0 ) sets all LEDs status_clear(0xf) clears all */ void status_clear(int num) { } PFOUT &= ~(num & 0x0F);

48 There are some Things You Should Know now that we will discuss in detail in a few weeks. About the oscillator About the serial port

49 Set The Oscillator If you don t explicitly set the oscillator, your program will use whatever it was last set to. // unlock the oscillator control register OSCCTL = 0xE7; OSCCTL = 0x18; // follow with ONE of these TWO settings // A0 = 1010_0000 = internal 5.5 MHz OSCCTL = 0xA0; // 61 = 0110_0001 = external Hz OSCCTL = 0x61;

50 To use the serial port #include <zneo.h> #include <sio.h> #include <stdio.h> void main(void) { OSCCTL = 0xE7; OSCCTL = 0x18; OSCCTL = 0x61; // MHz init_uart(_uart0, , 57600); } printf("hello World\n");

51 On The Serial Port The CLOCK passed to the INIT_UART() should match the oscillator speed set. If they don t, you will not get the baudrate you think you should get.

52 On The Serial Port Don t forget to enable the C Runtime

53 Careful, Clear, concise coding will help you in the long run!

Systems Programming. Lecture 4 Z16 Architecture and Programming

Systems Programming. Lecture 4 Z16 Architecture and Programming Systems Programming www.atomicrhubarb.com/systems Lecture 4 Z16 Architecture and Programming Section Topic Where in the books Zilog Zilog Zilog Zilog UM197 (ZNEO Z16F Series Flash Microcontroller Contest