Part 1: Start up. Part 2: Add Instruction. Part 3: Another way to get data into a register

Transcription

1 Part 1: Start up Power on the DE2 (Lab 0 showed you how), and begin the project by doing the following: Create new project directory Copy lab1sof and lab1ptf to the new directory Copy code provided (lab01?s) to the new directory Configure the DE2 in Quartus II (Reference Lab 0 for instructions) Start the Altera Debug Client Create a new configuration Configure system with lab1ptf Configure program with lab1as Part 2: Add Instruction Enter the code below into a file (lab01as) [Save your work to the D drive! If you save to the C drive, it will disappear at the next reboot or when the computer crashes!] Then compile and load it into the Debug Client Utilize your ISR to understand the add instruction You may notice that there appear to be other instructions after the add instruction You might be wondering what good an add instruction is if it has no data to work on For this module you can enter the values into the registers directly Try enough different entries to cover all the special cases (positive + positive, negative + positive, etc) and run a test for each set of these values to see if you get the resulting values that you expect Single step please (If you just run the code, who knows where you will end up!) Do you know how to re-execute the single instruction without re-compiling and re-loading the same program? You might look at changing the value of the pc register (pc does not stand for politically correct) # lab01as Your Name add r2,r3,r4 Part 3: Another way to get data into a register Enter the code below into a file (lab01bs) Modify the configuration program to point at the new code Run (single step) the code and observe the results of each instruction The addi instruction can be used to load numbers into a register What is the difference between 1234 and 0x1234? You might try right clicking on the register values Note that the data values are actually buried in the assembler instructions Is this a problem? # lab01bs Your Name movi r2,1234 movi r3,0x1234 add r4,r2,r3 Page 1 of 7

2 Now replace movi r2, 1234 with addi r2, r0, 1234 and movi r3, 0x1234 with addi r3, r0, 0x1234 What s the difference between these instructions? Part 4: Possibly a better add routine Enter the code below into a file (lab01cs) Now single step through the code and observe results What s wrong with hardcoding values into your assembly program? Are there reasons to do the code this way? Is there a limit on the range of values that can be entered into a register with this method? The data values in this case are stored exactly the same way as in Part 3 # lab01cs Your Name equ NBR1,45 equ NBR2,0x56 movi r3,nbr1 movi r4,nbr2 add r2,r3,r4 Part 5: Is this any better? Enter the code below into a file (lab01ds) Now single step through the code and observe results Is there a limit on the range of values that can be entered into a register with this method? In this case the data values are stored separately from the program code You should be able to see the data values in the disassembled region just after the stw instruction Note that the value for NBR3 displays the same value of all f s even after executing the stw instruction You need to go to the memory tab and display memory starting at 0; refresh memory to see the value change # lab01ds Your Name movia r5,nbr1 ldw r3,0(r5) movia r6,nbr2 ldw r4,0(r6) add r2,r3,r4 movia r7,nbr3 stw r2,0(r7) NBR1: word 0x NBR2: word 0x NBR3: word 0xffffffff Page 2 of 7

3 Part 6: Halt Program Controlling the program counter to make sure that we always know what instruction is going be executed next is very important But what do you do at the end of a program? How do you affectively stop the processor? You can cause the program to go into a very tight loop of one instruction, and that way you can make sure that the program will not do anything unwanted But you have also rendered the system useless until it is reset Load and run the following program Hit the Run button and pause a few seconds later Can you catch the program counter at any value other than 0? Does placing the branch instruction on the same line as the all_done label make the execution any faster? # lab01es Your Name Part 7: Simple Loop The process of writing code with a step-wise refinement approach can sometimes lead to a solution much faster than you might assume So we will begin by adding one more operation to our list of instructions that we can use, and that is the br instruction We will also expand on the concept of a label or symbol followed by a colon : The _start label is a label that was made visible outside of the current partial program module with the global directive You can use other labels without making them global as in the case of the and labels The following code will just loop forever Using the debugger, watch the value of the r2 register Labels do not take up space in the executable code produced, so adding the label only marks the end of the loop structure and visually identifies the end of the loop code Do we need to worry about end of program situation here? # lab01fs Your Name movi r2,0 Page 3 of 7

4 Part 8: Slightly more intelligent loop We could do something useful by adding a sum register (r4) that just summed the values of the counter register (r2) However, this is still not really satisfying as it doesn t really do anything in a general manner It would be nice to sum up any list of numbers (In the debugger, you ll see that addresses beyond the end of the loop contain unknown values or instructions) # lab01gs Your Name equ MAX_LOOPS,5 movi r3,max_loops movi r2,0 movi r4,0 beq r2,r3,loop_end add r4,r4,r2 Page 4 of 7

5 Part 9: Loop with initialized data from memory This time we will get a count of the number of values to sum, and sum those numbers As we did in lab01ds, we will get the count and values from memory and store the results back into memory For this version we will stick with the numbers that produce a result that we already know from previous results # lab01hs Your Name movia r5,vcount # address of value count ldw r3,0(r5) # value count movia r7,values # address of values movi r2,0 movi r4,0 # zero counter # zero sum beq r2,r3,loop_end ldw r6,0(r7) add r4,r4,r6 addi r7,r7,4 # get value # add to sum # position to next value movia r7,sum stw r4,0(r7) # address of SUM # store SUM VCOUNT: word 5 VALUES: word 1,2,3,4,5 Page 5 of 7

6 Part 10: Now try new data values # lab01gs Your Name SAME AS BEFORE VCOUNT: word 10 VALUES: word 1,2,3,4,5,6,7,8,9,10 Part 11: Or something more interesting What will happen if we change VCOUNT to another value without changing anything else? # lab01gs Your Name SAME AS BEFORE VCOUNT: word 8 VALUES: word 2,3,5,7,11,13,17,19 Part 12: Interface to external device To output information to some devices requires us to write data in a manner similar to writing to memory As we did to write to the SUM memory location, we can write to device with a stwio instruction Compile and load the following code into the debugger Then exercise it with the following values and observe the results # lab01hs Your Name stwio r4,0(r7) Set register r4 to 0x and r7 to 0x8818 (HEX port) Now execute the stwio instruction Now change r7 to 0x8800 (LEDR port) and re-execute the stwio operation Page 6 of 7

7 Now let s integrate the display functions into our summation code This only requires two new instructions to be added Place a break at the second stwio instruction, and instead of using the single step button try using the run (or continue program execution ) button # lab01is Your Name equ LEDR,0x8800 equ HEX,0x8818 movia r5,vcount # address of value count ldw r3,0(r5) # value count movia r7,values # address of values movi r2,0 # zero counter movi r4,0 # zero sum movia r8,ledr movia r9,hex # address red LED port # address 7 segment port stwio r2,0(r8) # *** NEW INSTRUCTION *** beq r2,r3,loop_end ldw r6,0(r7) # get value add r4,r4,r6 # add to sum stwio r4,0(r9) # *** NEW INSTRUCTION *** addi r7,r7,4 # position to next value movia r7,sum stw r4,0(r7) # address of SUM # store SUM VCOUNT: word 8 VALUES: word 2,3,5,7,11,13,17,19 This completes the code for this lab by using the stepwise refinement approach You have learned a lot of new instructions and produced some working code Now, complete the practical assignment listed as a deliverable on the lab cover sheet Move your project directory to team? drive Page 7 of 7