Lab 5: SDC Virtual Machine

Transcription

1 Lab 5: SDC Virtual Machine Due Date: Thursday 3/9/ :59PM This lab covers the material in lectures You will be creating a virtual (software-based) implementation of a basic, decimal-based Von Neumann machine. You could also call this an emulator. Note that this is a two-part lab. What we ll end up with is a line-oriented command-line program that reads in initial memory contents from a file and then lets the user enter commands to execute the program s instructions and inspect registers and memory (much like an interactive debugger such as gdb). Your goal is to fill in all of the missing functionality in lab5.c which is indicated by FILL ME IN comments. You should add your own code in these locations. Coding Assignment (100 points total) For this lab, you will be initializing the CPU, the memory (from a file), and the registers. You will then dump out (print) the state of the CPU and registers, and the contents of memory interpreted both as raw decimal data and as decoded instructions. 1. Initialize the CPU, set the general purpose registers (GPRs), the IR, and the PC each to When you run your program command (./lab5), you must provide the file name for an SDC (.sdc) file as an argument. 3. In its simplest form, an SDC data file is a sequence of lines containing one integer per line. E.g., The first number goes into memory location 00, the second into 01, etc. Your program will stop reading if you hit end-of-file (EOF) or if you run out of memory locations (by trying to read past location 99). Your program will also stop if you read in a sentinel value, i.e. one outside the range (A sentinel value just tells you that you ve run out of input.) 1

2 4. The SDC data file can contain comments, whitespace, and blank lines. If a line is blank or begins with something that isn t a number, ignore the whole line. If a line begins with a number, read that number into memory but ignore any text after it. E.g., the following input would be equivalent to the simple example above. This is a comment 1234 so is this 3456 ; this too (ignore the 3 5 7) 0 note leading space 2568 This line is ignored too this sentinel tells us to stop reading 1111 so everything after it is ignored 5. Dump (print) the contents of the CPU and memory. Most of the formatted printing is done for you. You just have to fill in the functions which generate the data to print! One of these functions will take the IR and decode the current instruction. Your solution s output should match the provided solutions output exactly. Use the techniques mentioned in previous labs for detecting differences. When you print out memory, note that you will skip locations whose contents contain zero. Here is what it will look like when you run the solution with t1.sdc: $>./lab5-soln tests/t1.sdc === SDC Virtual Machine Part 1 === Initial CPU: CPU STATE: ========== PC: 00 IR: 0000 RUNNING: 1 R0: 0 R1: 0 R2: 0 R3: 0 R4: 0 R5: 0 R6: 0 R7: 0 R8: 0 R9: 0 Encountered sentinel at location 25. Exiting read loop. value, instr (nonzero values LDM R1, 78 2

3 @ LDM R2, ADDM R1, ADDM R2, ST R1, LD R3, ADD R3, NEG BR BR BRP R1, BR BRN R2, BR PUTS HALT Getting the Code Get the lab5 code by logging into fourier and running the following: $> cp /home/khale/handout/lab5.tgz. $> tar xvzf lab5.tgz l5/ l5/lab5.c l5/tests/ l5/tests/t4.sdc l5/tests/t8.sdc l5/tests/t10.sdc l5/tests/t1.sdc l5/tests/t3.sdc l5/tests/t6.sdc l5/tests/t7.sdc l5/tests/t5.sdc l5/tests/t2.sdc l5/tests/t9.sdc l5/test_harness l5/makefile l5/lab5-soln l5/lab5.h $> cd l5 $> make gcc -Wall -Wno-unused-variable -Wno-unused-but-set-variable -std=c99 -lm $> ls 3

4 lab5 lab5.c lab5.h lab5-soln Makefile test_harness tests You ll see a few extra files this time. One of them is a header (.h) file. In larger C programs, it is a convention to put function prototypes, structure definitions, typedefs, and #defines in header files, especially when they could potentially be used in other.c files in the project. In the lab5.h header you ll see the definitions for the structs and typedefs used throughout the program and the function prototypes as well. You can see how to run the program by running it without an argument: $>./lab5 === SDC Virtual Machine Part 1 === Usage:./lab5 <sdc file> Your job here is to fill in the functions in lab5.c which have FILL ME IN comments written in them. See the comments in the code for further instructions. I ve also included a test harness for you to test your code. You can run it like so: $> make test # Testing lab5... Test 0 - [FAIL] Test 1 - [FAIL] Test 2 - [FAIL] Test 3 - [FAIL] Test 4 - [FAIL] Test 5 - [FAIL] Test 6 - [FAIL] Test 7 - [FAIL] Test 8 - [FAIL] Test 9 - [FAIL] Test 10 - [FAIL] 0 out of 11 test cases passed Notice that the code will initially fail all the test cases. Your job is to make it pass them all. These are example.sdc files, and I ve included them in a separate directory named tests. You are free to add your own test programs in.sdc files in that directory. For grading, we will be using other tests in addition to the ones in this directory, so make sure you pass them all. A good strategy here to get started is to start with the main() function and work your way down based on the functions that are called from there. Hand-in Instructions Make sure to put your name on your submission. Submissions without names will be given zero points! For code, this means put a comment at the top of your C file with your name on it. For the code, you must hand it in digitally. I ve made this a bit easier this time. Once you re happy with your code, in the directory where your code is (l5), run the following on fourier: $> make handin 4

5 Late handins If you re turning in your code late, you ll need to it to me after having created a.tgz file from it on fourier. Run the following in your l5 directory on fourier: tar cvzf whoami -lab5.tgz lab5.c lab5.h Makefile Note that those are backticks, not quotes surrounding the whoami command. whoami is a command that prints out your username. You ll then want to use scp or Filezilla or the equivalent to get that file off of fourier onto your local machine and send it to me as an attachment. Programming Notes You re welcome to add functions that aren t already present in the skeleton (e.g. helper functions). To read in a line of text and see what s in it, we can t use scanf because it ignores line ends. The skeleton uses fgets to read a line from the data file (as a string of characters) into a buffer; then it uses sscanf to do a formatted read of the buffer. First, the skeleton uses fgets to read a line of text from the data file into a buffer. fgets returns a pointer to char. If the pointer equals NULL, we hit end-of-file. (If it successfully reads data, fgets returns a pointer to the buffer you used.) The usual case is that fgets copies characters from the file into the buffer until it sees the end of the line ( \n ). (It does copy the \n into the buffer.) There s also a safety feature: We give fgets the length of the buffer; if fgets reaches the end of the buffer before seeing the \n, it stops, so as not to overrun the end of the buffer. This is a safety feature because a standard way to attack a program is to fill memory with evil code by writing way past the end of a buffer. After fgets reads characters into the buffer, we can use sscanf to read data from the buffer. Instead of scanf(format, &var1,...), which reads data from standard input, we use sscanf(string, format, &var1,...) to read data from the string. Like scanf, sscanf returns the number of items that that particular call managed to read, so we can tell whether or not the read found everything. E.g., x=sscanf(buffer, "%d %d", &y, &z); tries to read two integers from the string buffer into variables y and z. It sets x to 2,1, or 0, depending on whether it sets both y and z or just y or neither y nor z. Note: Just because scanf or sscanf doesn t find what it s looking for (e.g., by not finding an integer when reading with %d), that doesn t always mean you hit end-of-file or end-of-string; it might be that there was more input but it just didn t look like an integer. 5

6 Illinois Institute of Technology SDC ISA Reference Note here that the mnemonic for BRC will actually be either BRN or BRP depending on the sign. 6