680x0 behaviour question

[FrenchShark]

Hello,

I am trying to make a 680x0 emulation in VHDL.
I have a question concerning the shift operation:
- Freescale documentation says : the shift value is modulo 64.
- The 68k emulator I am using (EASy68k) uses a shift value modulo 32.

Can someone execute the following code under AsmOne (with a real Amiga !)? :

moveq  #39,D0
move.l #$000000FF,D1
lsl.b  D0,D1
rts

According to Freescale, D1 must contain $00000000.

Regards,

Frederic

[AmiDog]

Not in front of my Amiga right now, but yes, shifts on the 680x0 and PPC are modulo 64 while they are modulo 32 on x86 and MIPS while ARM seems to use modulo 256...

[ChaosLord]

Using Devpac on my Amiga Real Machine (68060)
D1 ends up with $00000000

[Piru]

The 68k emulator I am using (EASy68k) uses a shift value modulo 32.

Ouch. Maybe you should use some more proven emulation, such as the one in UAE?

[FrenchShark]

@ChaosLord

Thank you, it looks like I found a bug in EASy68k :-)

@Piru

I did not want to install UAE just for few lines of ASM testing.

Anyway, thank you guys.
I can finish the ALU shifter now (the hardest part is actually the V flag management).

Frederic

[ChaosLord]

I think he meant "look at the source code of UAE"  :-)

[ChaosLord]

How fast can your VHDL chip go?
Could it do 25Mhz?

[alexh]

ChaosLord wrote:
How fast can your VHDL chip go?
Could it do 25Mhz?

VHDL isnt a chip, it's a language. The speed it synthesises to is dependant on the FPGA (or ASIC technology) it is going to be implemented with.

Name an FPGA and I am sure that he'll be able to tell you what speed it will run at in that FPGA.

[ChaosLord]

In that case I would like to ask which FPGA chip is he going to use?

And how many cycles does it take to do a moveq #0,d0 in your implementation?

[FrenchShark]

I am the lucky owner of a Stratix II board :-).

I want to create a risc CPU with the ALU of a 68000.
If I do it well, I should achieve 100+ MHz operation, with the emulation layer this should translate to 10-20 MIPS.

[FrenchShark]

Hello,

I have a second question, does the following code set the X, N and C flags ?

        MOVEQ   #9,D0
        MOVE.L  #$FF,D1
        ASR.B   D0,D1
        RTS

The emulator just set the N flag.

[ChaosLord]

ccr #$00000019 ac ng nz nv cy

[FrenchShark]

Thank you!

another bug in EASy68k :-)

[Piru]

I did not want to install UAE just for few lines of ASM testing.

Well, winuae + asmone can be quite handly when quickly testing stuff. And WinUAE 68k emulation is quite accurate, at least more than that of the EASy68k.

WinUAE emu still has some small differences to the real thing, but nothing really important.