anotherlin/z80emu

A free portable Z80 emulator.

z80emu's Issues

Where is SystemCall defined?

N/A

Mode2 Interrupts

It looks like the mode 2 interrupts implementation is bad. It is actually jumping to the location generated by the interrupt instead of reading the actual address to jump to from that location. I made some modifications to make it dereference that interrupt vector and it seems to work great.

halted state is not kept between emulation calls

Hello. If you run the cpu for N cycles, a HALT instruction occurs, then you run it for more cycles, the next run it will not recall that it is halted. This would not matter if you're interrupting it between two emulation calls, but if you're not, it needs to remember that it is halted. I fixed it by adding a halted flag in the state struct and that flag is set to 0 when the interrupt function is called. You might have a cleaner way of implementing it, so I won't submit a patch.

Inconsistent execution ld sp,ix

I am trying to use this emulator to test a compiler and it looked it was working fine,
but now I am facing some issues when dealing with the stack.

"ld sp, ix" behaves inconsistently depending on the context; which results in wrong sp value.

BIT n,(HL) and XY flags

Hello, thank you for this emulator.
For the X and Y flags you take bit 3 and 5 from the L register.
According to this document http://www.grimware.org/lib/exe/fetch.php/documentations/devices/z80/z80.memptr.eng.txt it is a little bit more complicated...
Is it luck that your implementation results in correct values with ZEXALL.COM?
Or is that document wrong?

PC value in context

Hello,

Can you please help me why I got 0x0001 as PC value? Thank you!

https://github.com/iddq/z80emu/blob/master/tnc2.c

 ./tnc2  | head -10
Testing "testfiles/TNC2118A.ROM"...
out: 223 value: . 2, PC: 0x1
out: 223 value: U 85, PC: 0x1
out: 223 value: . 2, PC: 0x1
 in: 223 value: 2
out: 223 value: . 2, PC: 0x1
out: 223 value: . 253, PC: 0x1
out: 223 value: . 2, PC: 0x1
 in: 223 value: 2
 in: 221 value: 0

Assuming that char is signed

Hi, thanks for putting up this project at github. I've currently using it in a project running on a ESP8266 (Xtensa LX106 CPU) and ran in to some troubles with the code expecting that a char is signed in a few places.

The xtensa compiler assumes that a char is signed unsigned.

        int sum1=100; int sum2=100; int sum3=100;
        int value=-5;
        char c=(char)value;
        unsigned uc=(unsigned char)value;   
        signed char sc=(signed char)value;
        sum1+=c;
        sum2+=uc;
        sum3+=sc;
        os_printf("sum+c=%d sum+uc=%d sum+sc=%d\n",sum1,sum2,sum3);
        // ESP8266 --> sum+c=351 sum+uc=351 sum+sc=95
        // GCC X86 --> sum+c=95  sum+uc=351 sum+sc=95

This screwed up the implementation of relative jumps (something that zexall didn't detect!) and also made zexall report failures for the shift and rolls instructions. I spent a good while trying to figure out what what wrong with the shf/rol implementation, but when I by chance discovered the bug in the relative jumps I then realized what was the cause and it was an easy fix to get it all working perfectly.

Would you be interested in a pull request for my fix of these issues?

Added feature

Not a bug just a new feature i added.

When EI (enable interrupts) occur i need to know if there is an interrupt waiting so i should leave the emulating loop so i added a new function also i am not sure if it is a bug but i also changed the
number_cycles += 4; with number_cycles = elapsed_cycles+4; so the loop will end after 4 cycles.

`
case EI: {
bool c;

							state->iff1 = state->iff2 = 1;

#ifdef Z80_CATCH_EI

							state->status = Z80_STATUS_FLAG_EI;
							goto stop_emulation;

#else

							/* See comment for DI. */

						   // number_cycles += 4;
						   //TODO:Ask if there is an interrupt
						   // getint before exiting
						   Z80_GetInterrupt(c);
						   if (c) {
							number_cycles = elapsed_cycles+4;
						   }
                            break;

#endif

					}

`

on user.h just added a new macro

#define Z80_GetInterrupt(x)
{
(x) = MyZ80->Z_GetInterrupt();
}

MyZ80 is a Delphi class i use to communicate with C++ Builder so people just put there their own function that tells Z80 if there is an interrupt waiting in order to break the emulation.
If i don't use this the emulation is very slow because it exits the loop every 100 cycles which interrupts get enabled and then disabled again on the machine that i emulate.

Anyway i am ok with these changes just letting you know in case you wanted to implement something like that for everyone to use.

Interrupt modes

Hi,

i took the liberty of using your emulator on my project that emulates a 1980s home computer and i think there is a bug on selecting the Interrupt Mode.
The byte that Selects IM 1 are ED 56 and the original code selects IM 0
I replaced that code with this one and it worked ok (haven't tested the other modes):
``
case IM_N: {

							/* "IM 0/1" (0xed prefixed opcodes 0x4e and
                             * 0x6e) is treated like a "IM 0".
							 */

							if ((opcode & 0x08)) //IM2
								state->im = Z80_INTERRUPT_MODE_2;
							else if ((opcode & 0x10))

									state->im = Z80_INTERRUPT_MODE_1;

							else
									state->im = Z80_INTERRUPT_MODE_0;

                            break;

``

Very good work.

license

please clarify what is the license in the classical "COPYING" file

2 instructions in one step

First, thanks for this project, it helps me a lot ^^ I'm trying to create a java z80 just for fun and I'm using z80emu step by step as a reference to correct my emulator and it's a huuuuuuge help to be able to step by step zexdoc and zexall !

But while running zexdoc at step 3115 we have a DI instruction:

1d2e f3             DI
1d2f ed 73 8d 1d    LD (1d8d),SP
1d33 31 05 01       LD SP,0105

step=3115
a=cd f=8b b=00 c=09 d=02 e=03 h=00 l=2c i=00 r=0d ixl=00 ixh=00 iyl=00 iyh=00 
sp=c8f0 pc=1d2e iff1=0 iff2=0 m=0 
mem=f3 ed 73 8d 1d 
stack=2c 00 03 02 09
(hl)=00 (de)=3c (ix)=d3 00 00 00 00 (iy)=d3 00 00 00 00

And at next step, the status is:

step=3116 
a=cd f=8b b=00 c=09 d=02 e=03 h=00 l=2c i=00 r=10 ixl=00 ixh=00 iyl=00 iyh=00 
sp=c8f0 pc=1d33 iff1=0 iff2=0 m=0 
mem=31 05 01 fd e1
stack=2c 00 03 02 09 
(hl)=00 (de)=3c (ix)=d3 00 00 00 00 (iy)=d3 00 00 00 00

PC has moved to address 1d33 instead of 1d2f and R has moved from 0d to 10.
It seems that 2 instructions has been executed instead of just DI.

There is not wrong z80 implementation, but 2 steps have been executed instead of one, is this a design choice ?

Thanks