Simple Computer 2010 (CS2010)

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DEPARTAMENTO DE TECNOLOGÍA ELECTRÓNICA ESCUELA TÉCNICA SUPERIOR DE INGENIERÍA INFORMÁTICA Simple Computer 2010

Introduction and goals Session goals are the following: Using and programming the CS2010 Watching the control

input-output operations For this session, a CS2010 system has been implemented 1 Figure 1.

1 DEPARTAMENTO DE TECNOLOGÍA ELECTRÓNICA ESCUELA TÉCNICA SUPERIOR DE INGENIERÍA INFORMÁTICA Simple Computer 2010 (CS2010) Computer Structure 1. Introduction and goals Session goals are the following: Using and programming the CS2010 Watching the control unit behaviour Watching the data unit behaviour Writing and testing a simple CS2010 program including input-output operations For this session, a CS2010 system has been implemented 1 Figure 1. The system includes de following components: using the Digilent Basys2 board shown in the CPU the code memory the data memory memory-mapped input-output devices a debug unit 1 The implementation has been carried out by Jonathan Ruiz Páez

Computer Structure 2 Figure 1: prototyping board used in this session The input-output devices have been mapped into data memory space as shown in the following table: ADDRESS DIRECTION DEVICE

2 Computer Structure 2 Figure 1: prototyping board used in this session The input-output devices have been mapped into data memory space as shown in the following table: ADDRESS DIRECTION DEVICE DESCRIPTION $80 input Switches Each of the bits of this location let us know if the corresponding switch is activated. So, bit 7 will be equal to 1 when switch 7 is active, bit 6 will be equal to 1 when switch 6 is active, and so on. $81 input Buttons The 4 least significant bits of this location let us know is the corresponding button is pressed. So, bit 3 will be equal to 1 when button 3 is active, bit 2 will be equal to 1 when button 2 is active, and so on. The 4 most significant bits of this location are always equal to 0. $82 output least significant digits of the display $83 output most significant digits of the display The content of this memory location is shown in the right part of the display in hexadecimal. The content of this memory location is shown in the left part of the display in hexadecimal. The debug unit communicates with the PC through the RS232 so it can read and write the program and data memories. providing these functionalities: Also, the debugging units makes it possible to debug the uploaded program by

3 Computer Structure 3 cycle by cycle execution instruction by instruction execution memory and register inspection control lines inspection enabling/disabling the CPU clock The user can interact with the debug unit by using the software described at the appendix. 2. Previous work 1. Read the appendix and learn about the CS2010 assembler format. 2. Write a CS2010 subrutine that writes in register R7 the product of R5 and R6 (using unsigned notation). 3. Write a CS2010 program that, by using the previous subrutine, calculates the product of 22 and 10 and writes the result in memory location Write a table describing which signals are activated and which register transfers are carried out in each clock cycle during the execution of the 2 first instructions of the previous program. 5. Using the previous subrutine, write a CS2010 implementing the following algorithm: DO WHILE BUTTON 0 IS NOT PRESSED DO NOTHING END WHILE R5<-NUMBER CODED BY THE SWITCHES WHILE BUTTON 3 IS NOT PRESSED DO NOTHING END WHILE R6<-NUMBER CODED BY THE SWITCHES R7<-R5*R6 SHOW R7 AT THE DISPLAY FOREVER 6. Make sure that the syntax of the programs you wrote is right by using the software available at the web page. WARNING: It is mandatory to bring the files with the programs to the laboratory session, and you must check the syntax by using the provided software before the session. 3. Lab work 1. Set the board Mode Jumper (JP3) to ROM.

4 Computer Structure 4 2. Connect the board to the PC RS232 port (look at Figure 1 to see how to connect the RS232 expansion to the board). 3. power the board by connecting it to the PC USB port. 4. Upload the program that calculates 22x10 to the CS2010 code memory as described at the appendix. 5. Execute the first 2 instructions cycle by cycle. Check if the register transfers and data transfers you expected are carried out. 6. Execute instruction by instruction the 2 following lines. Check if effect of the execution is what you expected. 7. Enable the clock to execute the remaining instructions. Disable it again to check the final result. 8. Upload the program implementing the algorithm of section 5 of the previous work and execute it enabling the clock. Check if the program works as expected by multiplying several numbers. NOTE: If the software warns you that it was not possible to carry out the connection despite you connected the RS232 extension properly, it may be possible that the prototyping board is not configured yet to implement the CS2010. Is so click on the icon configurar BASYS2 para CS2010 and, after the writing, turn the board off and turn it on again. Appendix 1: CS2010 assembler format The binary code executed by any processor is called machine code. Writting machine code directly is not practical. Instead, we will write the programs using a more easily readable language called assembler language. Programs written in assembler can be translated to machine code by using a tool that is also called assembler. This action is called assembling. A CS2010 assembler program can contain 3 types of lines: blanc lines: they contain just space characters, tab characters and/or comments. These lines are ignored by the assembler. instruction lines: they describe a CS2010 instruction by using the mnemonics described in class. If an instruction requires a numeric operand, it can be specified in any of the following ways: using a decimal numeral: in this case the numeral can be preceded by a sign (+ or -). using a binary numeral: in this case the numeral must be preceded by prefix 0B and must include exactly 8 bits. using an hexadecimal numeral: in this case the numeral must be preceded by prefix 0x or $ and must include one or two hexadecimal digits. using a tag: a tag is an alphanumeric string that is assigned an 8-bit value. The first character of the tag must must be a letter. We will see how to assign values to tags later. Examples of valid numerals are 1234, +2, -1, 0b , $4F, 0x32, $3. Examples of invalid numerals are 12F3, +0b , 0b , 0b10, 0x023. directive lines: they are used to order the assembler to carry out several actions. The CS2010

5 Computer Structure 5 assembler directives are the following: EQU directive: make it possible associating a value to a tag. Its syntax is.equ <tag> = <numeral>. After finding such a line, the assembler will substitute every occurrence of the tag in the instruction lines by the associated value. Note that this lines will not have any associated instruction in the resulting assembled program. OPCODE directive: make it possible inserting instructions by indicating its machine code explicitly. Its syntax is.opcode <most_significant_byte>, <least_significant_byte> w h e r e <most_significant_byte> must be a numeral and <least_significant_byte> can be a numeral or a tag. There is a second way to assign values to tags: instruction lines as well as lines using the OPCODE directive can be preceded by a prefix in the form <tag> :. This makes the assembler to assign the address of the memory location corresponding to the instruction of that line to the tag. Assembler programs using jump instructions can be make clearer by assigning tag values in this way. Another way to make programs more readable is adding comments at the end of lines. Comments start with character ';'. Any text between this character and the end of line will be ignored by the assembler. Finally you must take into account that the assembler is not case-sensitive, i.e. it does not distinguish between lowercase and uppercase letters. An example of CS2010 program written in assembler is shown bellow:

Computer Structure 6 ;this is a comment and will be ignored by the assembler LDI R0,15; this will write 15 in R0 ;space and tabs are ignored LDI R1,$0F ;this will write 15 in R1 LDI R2,-1 ;this will

6 Computer Structure 6 ;this is a comment and will be ignored by the assembler LDI R0,15; this will write 15 in R0 ;space and tabs are ignored LDI R1,$0F ;this will write 15 in R1 LDI R2,-1 ;this will write 225 in R2 ;this is another comment followed by blanc lines.equ minus1=0b ; this will not generate machine code.equ one=1 LDI R3,0 loop: SUBI R0, one BRCS finishthis st (r3), r0 ; lowercase or uppercase: it doesn't matter ADDI R3, ONE jmp loop FINISHTHIS: STOP ;the 14 first memory locations will be written from 14 to 1 Appendix 2: Debugging and programming software For interacting with the debug unit we will use the software installed in the lab PCs. This software is available for download in the web page. To launch it just click on the corresponding icon of the desktop. The following window will appear: Figure 2: CS2010 debugging software The upper part of the window contains a set of controls to interact with the CS2010 debug unit: Puerto Serie field: This field contains the path for the PC RS232 port connected to the board. Do not change it. Código (BIN) field: This field must contain the path of the binary file whose content will be written in the program memory when the processor is initialized. After filling it, the code will be disassembled and shown on the Desensamblado field. We will not have to fill in this field since we will use assembler files.

Computer Structure 7 Código (ASM) field: This field must contain the path of the assembler file corresponding to the program that will be written in code memory when the processor is initialized.

7 Computer Structure 7 Código (ASM) field: This field must contain the path of the assembler file corresponding to the program that will be written in code memory when the processor is initialized. After filling it, the file will be assembled informing about possible mistakes and will write the path of the resulting binary file in the Código (BIN) field. We will use this field to check our programs. Memoria Datos field: if we want to initialize the data memory with the content of a binary file, we can write its path in this field. Conectar button: when this button is pressed the software establishes a connection with the debug unit through the RS232 port, orders to initialize the CS2010 and to write the program and data memories with the content of the specified files. Only after this we will be able to interact with the debug unit. Mostrar Unidad De Datos button: when this button is pressed the following window appears: Figure 3: CS2010 data unit During cycle-to-cycle execution the active (high) signals will be highlighted in this window. Habilitar Reloj / Deshabilitar Reloj button: If the CS2010 clock is disabled, pressing this button will enable it so the program can be executed autonomously. If the clock is enabled, pressing this button will disable to make it possible to inspect the state of the processor and memory. Activar Start button: When this button is pressed, an high pulse is generated in the start signal of the CS2010. Ejecutar Un Ciclo button: If this button is pressed the debug unit will enable the clock for just a cycle. Ejecutar Una Instrucción button: If this button is pressed the debug unit will enable the clock till the current instruction finishes or till the wait state is reached. When the CS2010 clock is disabled, the system state is shown, including:

8 Computer Structure 8 data memory content registers content control lines state value of the common data bus and of the buses connected to the ALU Also, the current instruction will be highlighted. The content of the data memory can be edited manually. It is also possible to save the content of the data memory in a file by pressing the Guardar Memoria Datos button.

Introduction to Verilog and XILINX

DEPARTAMENTO DE TECNOLOGÍA ELECTRÓNICA ESCUELA TÉCNICA SUPERIOR DE INGENIERÍA INFORMÁTICA Introduction to Verilog and XILINX Lab Session Computer Structure WARNING: A written solution of the preliminary