Here is a very minor update to Ian Piumarta's excellent 6502 simulator. I was in need of a simple command line environment to test my Apple 1 PLASMA VM - running a full blown emulator was just too inconvenient to test my code. However, lib6502 didn't easily allow for tracing executing code which is what I was looking for. So, I made some very minor changes to the spectacular C macros he created to allow for single stepping. And I do mean his macros are spectacular; really, you should check them out.
Now, by setting a flag in the mpu structure such as:
Code:
mpu->flags |= M6502_SingleStep;
One can run the simulator and trace/single step the 6502 code for easy debugging:
Code:
while (M6502_run(mpu))
{
char state[64];
char insn[64];
M6502_dump(mpu, state);
M6502_disassemble(mpu, mpu->registers->pc, insn);
printf("%s : %s\n", state, insn);
}
This will display to the console:
Code:
PC=0677 SP=01FC A=6A X=10 Y=00 P=05 -----I-C : iny
PC=0678 SP=01FC A=6A X=10 Y=01 P=05 -----I-C : lda (F2),Y
PC=067A SP=01FC A=82 X=10 Y=01 P=85 N----I-C : sta E7
PC=067C SP=01FC A=82 X=10 Y=01 P=85 N----I-C : iny
PC=067D SP=01FC A=82 X=10 Y=02 P=05 -----I-C : lda (F2),Y
PC=067F SP=01FC A=0B X=10 Y=02 P=05 -----I-C : sta E8
PC=0681 SP=01FC A=0B X=10 Y=02 P=05 -----I-C : sty E4
PC=0683 SP=01FC A=0B X=10 Y=02 P=05 -----I-C : ldy #00
PC=0685 SP=01FC A=0B X=10 Y=00 P=07 -----IZC : lda (E7),Y
PC=0687 SP=01FC A=40 X=10 Y=00 P=05 -----I-C : dex
PC=0688 SP=01FC A=40 X=0F Y=00 P=05 -----I-C : sta D0,X
PC=068A SP=01FC A=40 X=0F Y=00 P=05 -----I-C : iny
PC=068B SP=01FC A=40 X=0F Y=01 P=05 -----I-C : lda (E7),Y
PC=068D SP=01FC A=0B X=0F Y=01 P=05 -----I-C : sta C0,X
PC=068F SP=01FC A=0B X=0F Y=01 P=05 -----I-C : ldy E4
PC=0691 SP=01FC A=0B X=0F Y=02 P=05 -----I-C : rts
PC=069B SP=01FE A=0B X=0F Y=02 P=05 -----I-C : jmp 00F0
PC=00F0 SP=01FE A=0B X=0F Y=02 P=05 -----I-C : iny
PC=00F1 SP=01FE A=0B X=0F Y=03 P=05 -----I-C : lda 15BF,Y
PC=00F4 SP=01FE A=62 X=0F Y=03 P=05 -----I-C : sta F7
PC=00F6 SP=01FE A=62 X=0F Y=03 P=05 -----I-C : jmp (0362)
PC=05DE SP=01FE A=62 X=0F Y=03 P=05 -----I-C : lda D0,X
PC=05E0 SP=01FE A=40 X=0F Y=03 P=05 -----I-C : sta BF,X
PC=05E2 SP=01FE A=40 X=0F Y=03 P=05 -----I-C : lda (BF,X)
PC=05E4 SP=01FE A=A6 X=0F Y=03 P=85 N----I-C : sta D0,X
PC=05E6 SP=01FE A=A6 X=0F Y=03 P=85 N----I-C : inc BF,X
It's simply based on the return value from M6502_run: 1 (or non-zero) means it is single stepping, 0 means error/exit. I sent email to Ian but he may not check that email address very often or is busy with real life. So I thought I would post it here if anyone is interested. It's part of the PLASMA project located here:
https://github.com/dschmenk/PLASMA/tree ... rc/lib6502The Apple1+CFFA1 code is in a1cffa.c which is a very simplistic version of an Apple 1 with CFFA1 card but sufficient for my needs.
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