The purpose of this assignment is to introduce you to how an assembler works, and to give you experience in reading and modifying a large existing program. Also, some experience in binary object file formats.
You are working at TIC, and your manager tells you that a key employee left and his project is unfinished. He wants you to finish it.
At asm8.tar is a partially working version of a PDP-8 assembler. This is needed to ship to customers on 10 Nov. It mostly works, but has a couple of problems:
In the binary format, the first 4 characters of a PDP-8 object file will be "OBJ8". Next, we will have two bytes which will store the 12-bit starting address for the object file. The PDP-8 has 12 bit words, so we need at least 2 bytes. We will put the high-order 6 bits in the first byte and the low-order 6 bits in the second byte. This same representation (two bytes, 6-bits in each, high-order first), will be used for all PDP-11 addresses and 12-bit values in the object file format.
After the magic number ("OBJ8") and the entry point address (2 bytes) will be a series of blocks. There will be as many blocks as necessary. Each block will be a set of bytes. The first byte (n) is the number of bytes in the entire block, including the first byte. So this first byte cannot be less than 1, and is of no practical value if it's less than 5. After this first byte will be a PDP-8 address (in the two byte format of upper 6 bits/lower 6 bits), followed by a set of values. The values will be PDP-8 12-bit values that are to be stored, starting at the address given, and continuing word after word, until we have exhausted the number of bytes at the beginning of the block.
EP: 067 064: 000 065: 000 066: F02 067: 664 068: 275 069: E21 ...would be represented as (printing the binary object file in hex):
4F424A380127330124000000003C023B393B373F3838 ...If we split this by structure we get:
4F424A38 0127 33 0124 0000 0000 3C02 3B39 3B37 3F38 ...
turnin --submit zxy program5 *.h *.c [Mm]akefile
Turn in enough that we can say "make asm8" to build an executable for testing. This can be a single C file (asm8.c) or it can be multiple C files and header files, with a Makefile that knows how to "make asm8".
Due Date: 10 November 2013