Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sat Dec 08, 2012 7:48 pm
If the monitor executes the wrong code, presumably it's either a misimplemented branch or a mistake in branching?
6502.org
The 6502 Microprocessor Resource
http://forum.6502.org/
My Arduino-Based 6502 Simulation/Emulation...thing?
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Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sat Dec 08, 2012 8:08 pm
Or a mistake in the flag handling.
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sat Dec 08, 2012 8:21 pm
Hee hee - that's what I meant to type!
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 4:47 am
One of the things that you can do is add some tracing to your simulator. For example, you can dedicate a memory location to a trace flag. Then whenever that location is set to 1, the simulator can start dumping a trace of the code that it's executing.
So, you can add some guards around the "help" code to turn this on and off. Or you can create a little more sophisticated command set (turn trace on, push current trace, turn trace off, pop trace status, reset trace status).
That way since "you know" your keyboard routine works (which is likely simply polling for a value), you can turn the trace off there while it loops for the next character, etc.
Run traces will tell you a lot. Add in some memory dumps to particular memory areas during the trace, that can help too.
Being on your own simulator makes things easier than if you were debugging this on a raw board, since you can get even greater insight into what the cpu is doing.
So, you can add some guards around the "help" code to turn this on and off. Or you can create a little more sophisticated command set (turn trace on, push current trace, turn trace off, pop trace status, reset trace status).
That way since "you know" your keyboard routine works (which is likely simply polling for a value), you can turn the trace off there while it loops for the next character, etc.
Run traces will tell you a lot. Add in some memory dumps to particular memory areas during the trace, that can help too.
Being on your own simulator makes things easier than if you were debugging this on a raw board, since you can get even greater insight into what the cpu is doing.
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 7:17 am
I've narrowed it down to either a bad ASL or JMP (address,X) opcode.
I'm pretty sure it's probably the JMP because that a CMOS opcode I coded myself. In the Monitor, it's used in a jump table to each command, and the addressing command is command 0. (Which is why that one works). The parser is fine and references the jump table via the X register perfectly. I'm really close on this one.
== EDIT ==
ASL is fine, X (address offset) is being incremented by 2 for every command in the list, which means I suck a C++ (known issue) and can't count correctly.
The offending command is here.
This is odd, because it appears to be coded right. I'm tracking the PC after this to see what happens...
I'm pretty sure it's probably the JMP because that a CMOS opcode I coded myself. In the Monitor, it's used in a jump table to each command, and the addressing command is command 0. (Which is why that one works). The parser is fine and references the jump table via the X register perfectly. I'm really close on this one.
== EDIT ==
ASL is fine, X (address offset) is being incremented by 2 for every command in the list, which means I suck a C++ (known issue) and can't count correctly.
The offending command is here.
Code: Select all
case 0x7c: // JMP INDIR,X
value = popWord(); // read address at PC and move up 2
addr = memReadByte(value) + (memReadByte(value+1)<<8); //read address at that location (Don't move PC)
addr = addr +regX; //add address given with what's in the X register
if (addr > 0xFFFF) {addr = addr - 0xFFFF;} //if the address is > 0xFFFF wrap around
regPC = addr; //move PC to the new address
break; //get the next opcode.
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 8:42 am
AUGH!!!! I FIGURED IT OUT!!!! It *WAS* a bad JMP command. evidently, I can't read instructions properly!
You add X to the address that is read after the opcode, not added the PC after the jump
The correct command implementation
System's running OK now, the assembler is printing out WAY to many spaces, which means I have another opcode to fix somewhere. I'm going to turn TSB back on and see if it works OK. Good news is that I can now somewhat code directly on the device and test opcodes as they run. That's pretty pimp.
=== EDIT ===
Yup TSB is broken, I'm using the NMOS way of doing it. I have a feeling I botched another indexer too. Some functions are hard-crashing and tripping my BRK handler. Oh well, onward and forward, right?
You add X to the address that is read after the opcode, not added the PC after the jump
The correct command implementation
Code: Select all
case 0x7c: // JMP INDIR,X
value = popWord();
value = value + regX;
if (value > 0xFFFF) {value = value - 0xFFFF;}
addr = memReadByte(value) + (memReadByte(value+1)<<8);
regPC = addr;
break;
=== EDIT ===
Yup TSB is broken, I'm using the NMOS way of doing it. I have a feeling I botched another indexer too. Some functions are hard-crashing and tripping my BRK handler. Oh well, onward and forward, right?
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 9:43 am
Hi - I think your starting point was code which inherited some 20 bugs from the original 6502asm.com emulator, so I recommend you try to inherit the fixes, or run Klaus' testsuite and find them yourself!
For example, see the changes dating from the beginning of August in https://github.com/BigEd/6502js/commits/master
Cheers
Ed
For example, see the changes dating from the beginning of August in https://github.com/BigEd/6502js/commits/master
Cheers
Ed
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 4:23 pm
halkun wrote:
AUGH!!!! I FIGURED IT OUT!!!! It *WAS* a bad JMP command. evidently, I can't read instructions properly!
You add X to the address that is read after the opcode, not added the PC after the jump
The correct command implementation
System's running OK now, the assembler is printing out WAY to many spaces, which means I have another opcode to fix somewhere. I'm going to turn TSB back on and see if it works OK. Good news is that I can now somewhat code directly on the device and test opcodes as they run. That's pretty pimp.
=== EDIT ===
Yup TSB is broken, I'm using the NMOS way of doing it. I have a feeling I botched another indexer too. Some functions are hard-crashing and tripping my BRK handler. Oh well, onward and forward, right?
You add X to the address that is read after the opcode, not added the PC after the jump
The correct command implementation
Code: Select all
case 0x7c: // JMP INDIR,X
value = popWord();
value = value + regX;
if (value > 0xFFFF) {value = value - 0xFFFF;}
addr = memReadByte(value) + (memReadByte(value+1)<<8);
regPC = addr;
break;
=== EDIT ===
Yup TSB is broken, I'm using the NMOS way of doing it. I have a feeling I botched another indexer too. Some functions are hard-crashing and tripping my BRK handler. Oh well, onward and forward, right?
If that is not enough, what about the case where value could equal 0xffff. The low byte comes from 0xffff but the high byte would come from 0x0000!
Here is the fix I suggest:
Code: Select all
case 0x7c: // JMP INDIR,X
value = (popWord() + regX) & 0xFFFF; /* fixes value > 0xFFFF */
addr = memReadByte(value) + (memReadByte((value+1) & 0xFFFF)<<8); /* fixes result when value = 0xFFFF */
regPC = addr;
break;
thanks!
Daryl
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 7:20 pm
The output looks like this....
and the relvant chunk of code
I'm going to bet it's that indexer again 
Code: Select all
65C02 Monitor v5.1.1 (12-02-12) Ready
By Lee Davison and Joshua Walker
(Press ? for help)
>E800
E800 - 4C
4C E9 4C 88 E8 4C B9 - E8 4C B6 E8 4C B1 E8 4C
>L
BDDC- ~^. FE 5E 15 INC $155E,X
BDDF- l.. 6C 0E 1C JMP ($1C0E)
BDE2- . 83
Code: Select all
JSR Print2Byte ; print address
LDA #$2D ; "-"
JSR Output ;
JSR Print2SP ; print " "
LDX #$01 ;---------
List4: LDY #$00 ;print up to 3 ascii chars...
List5: CPY HexDigCnt ; two spaces...
BCS List6 ; up to three hex chars...
LDA (StartAddr),Y ; two spaces
CPX #$00 ;
BNE List8 ;
JSR Print1Byte ;
BRA List7 ;
List6: CPX #$00 ;
BNE List7 ;
JSR Print2SP ;
List7: LDA #$20 ; " "
List8: AND #$7F ;
CMP #$7F ;
BEQ List9 ;
CMP #$20 ; " "
BCS List10 ;
List9: LDA #$2E ; "." use "." if not printable char
List10: JSR Output ;
INY ;
CPY #$03 ;
BCC List5 ;
JSR Print2SP ;
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 8:22 pm
BigEd wrote:
Hi - I think your starting point was code which inherited some 20 bugs from the original 6502asm.com emulator, so I recommend you try to inherit the fixes, or run Klaus' testsuite and find them yourself!
For example, see the changes dating from the beginning of August in https://github.com/BigEd/6502js/commits/master
Cheers
Ed
For example, see the changes dating from the beginning of August in https://github.com/BigEd/6502js/commits/master
Cheers
Ed
The problem with Klaus' test suite is that it makes the assumption there is some kind of tracer or stepping app outside the emulator that you can control. I don't have that luxury. Once I "Burn" a 6502 program onto the Arduino's AVR, I have no way to control the executing 6502 code or see what it's doing without the code itself outputting something to my little 16x2 display. (It can output out the serial connection too, that that's often busy running the code proper).
I'm running an emulator on an AVR, and the emulation code must fit a maximum of 256k (ROM) and only use 32k of ram. The actual memory map for the AVR looks like this.
0000-7FFF - AVR registers, stack, and Emulation variables
8000-FFFF - 6502 memory
The the space from 8000-FFFF is actually a 32k window and I can bank in and out of the 512K ram add-on. This means that the bottom half is mapped like this.
AVR RAM: 8000-FFFF (bank 0)
is equal to
6502 RAM: 0000-7FFF
and
AVR RAM: 8000-FFFF (bank 1)
is equal to
6502 RAM: 8000-FFFF
Did I mention that this ram is also not protected and I can overrun my emulation variables and stack into my 6502 memory space
So I don't have a lot of space to mess around in. It's also why the original Arduino emulation core only held 1024 bytes. Actually, I'm really quite shocked that this is running at all. I've made so many assumptions about how AVR works and how 6502 code runs, it shouldn't even be working. But now that It's halfway there, I guess I'm committed now.
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 8:28 pm
If the data at address $BDDC is FE 5E 15 then the "indexer" is working fine.
Hexdigitcnt is set to the # of bytes in this opcode ( 1-3).
The code uses the X reg as a flag to print either the ASCII character or the Hex value.
The Y register is an index to the memory, where Startaddr points to the opcode.
X is set to 1 at the start - this sets up the printing of the ASCII characters.
The address get printed ok, as does the - after it and 2 spaces.
Next, I see the ASCII character are printed - this happens when
jumps to List8. Good so far.
It seems to have a problem determining when to quit that part so it can do the DEX (below List10 - not shown)
to start printing the HEX values. While stuck, it prints spaces.
After much scanning, here is my suggestion:
Check that you CPY command is setting the C flag. It is for sure setting the Z flag or other routines would be failing. List5 and just after List10 are the only two places in the entire source that CPY is followed by BCC or BCS. There are some BPL/BMI that use CPY so be sure the N flag is being adjusted too.
Let me know if that helps!
Daryl
Hexdigitcnt is set to the # of bytes in this opcode ( 1-3).
The code uses the X reg as a flag to print either the ASCII character or the Hex value.
The Y register is an index to the memory, where Startaddr points to the opcode.
X is set to 1 at the start - this sets up the printing of the ASCII characters.
The address get printed ok, as does the - after it and 2 spaces.
Next, I see the ASCII character are printed - this happens when
Code: Select all
CPX #$00 ;
BNE List8 ;It seems to have a problem determining when to quit that part so it can do the DEX (below List10 - not shown)
Code: Select all
JSR Print2SP ;
DEX ;
BEQ List4 ;---------After much scanning, here is my suggestion:
Check that you CPY command is setting the C flag. It is for sure setting the Z flag or other routines would be failing. List5 and just after List10 are the only two places in the entire source that CPY is followed by BCC or BCS. There are some BPL/BMI that use CPY so be sure the N flag is being adjusted too.
Let me know if that helps!
Daryl
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 10:51 pm
I'm re-porting over the Java core with all the fixes. The current version is kind of a mess and I see where there are lots of improvements that need to be taken care of. I have a feeling when this is done, everything's going to be running much smoother.
or crumble under it's own weight
One of the two. Let's keep our fingers crossed
or crumble under it's own weight
One of the two. Let's keep our fingers crossed
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Sun Dec 09, 2012 11:50 pm
Well, that's interesting, while unifying the comparators, all of them broke, which means there was something systematically wrong with them. Now to put it back together again. So much fun.
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Mon Dec 10, 2012 1:10 am
You might be interested, or horrified, to see my emulator written in ARM assembly, where I tried to factor out as much commonality as I could - the result is very deeply nested macros.
https://github.com/BigEd/a6502/blob/master/emulator.S
My inspiration is Ian Piumarta's lib6502 core, written in C:
http://www.piumarta.com/software/lib650 ... /lib6502.c
and similarly dense with #defines - although his is the tidier code by a long way.
Cheers
Ed
https://github.com/BigEd/a6502/blob/master/emulator.S
My inspiration is Ian Piumarta's lib6502 core, written in C:
http://www.piumarta.com/software/lib650 ... /lib6502.c
and similarly dense with #defines - although his is the tidier code by a long way.
Cheers
Ed
Re: My Arduino-Based 6502 Simulation/Emulation...thing?
Posted: Mon Dec 10, 2012 2:04 am
Oh no, I'm happy programming my AVR in simple C.
Going through the code, I have discovered the opcodes that "kind of worked" and while reimplementing, broke them all the way. The comparators, bit testers, and bit shifters are now all broken, but better to have them broken then to have them sort of work. The cool thing is they have common core functions, so one I fix that, everything downstream will start working again.
In theory anyway.
Going through the code, I have discovered the opcodes that "kind of worked" and while reimplementing, broke them all the way. The comparators, bit testers, and bit shifters are now all broken, but better to have them broken then to have them sort of work. The cool thing is they have common core functions, so one I fix that, everything downstream will start working again.
In theory anyway.