VASM and BKPT

[fuzzylogic]

Hello it's me again with a VASM (or better said assembly question)

If I take a look into the MC68000 manual I see a mnemonic called BKPT. In the manual it is said that this is for MC68EC000, MC68010, MC68020,
MC68030, MC68040, CPU32.

When I try to assemble with VASM:

BKPT #7

It gives me an error:

error 9 in line 1 of "test.s": instruction not supported on selected architecture
>       bkpt    #7

So it won't let me do that. Strange since it should work for 68EC000.

Then I made a quick test: I put all the bits described in the m68k manual by hand for "BKPT #7" which gave me opcode $484F.

Bits:

0100100001001111 => $484F

After that I booted up my Amiga which has an Action Replay III attached. I put this opcode somewhere in RAM ($50000). Then I made a "d $50000" to see what the AR3 will show for this opcode, it was:

PEA A7

Does anyone have an explanation for this?

[Don_Adan]

I never heard about bkpt instruction. Perhaps pea is correct name.

[phx]

Originally Posted by fuzzylogic

If I take a look into the MC68000 manual I see a mnemonic called BKPT. In the manual it is said that this is for MC68EC000, MC68010, MC68020,MC68030, MC68040, CPU32.

vasm doesn't differentiate between 68000 and 68ec000. Maybe it should, as there are some more instructions which are 68ec000 specific, like move from SR.

EDIT: Checked the whole PRM, but BKPT remains the only instruction which differs between 68000 and 68ec000 (if this is not a bug in the Rev.1 M68000PM/AD. Move from SR is supervisor-only on 68ec000, but this makes not differences for the assembler. Interesting. Didn't know about BKPT on 68ec000.

Try to assemble for 68010 and

bkpt

will work.

PEA A7

Does anyone have an explanation for this?

Bug in the AR3 disassembler.

[meynaf]

Unless you are using special hardware that can catch the breakpoint acknowledge bus cycle (which is different between 68010 and 68020, missing in 68000 and perhaps again different in 68040+), bkpt does nothing but trigger an illegal opcode exception. So in some way, it works for 68000 too.
At least Devpac3 assembles it even in 68000 mode (phxass needs 68010).

[fuzzylogic]

Thanks guys for the clarification. I have never seen this before and was wondering.

[phx]

Does anybody know if the 68ec000 does a breakpoint acknowledge bus cycle? I would expect that. Otherwise there is no reason to document that the

bkpt

instruction is available on the 68ec000, but not on the 68000.

And is there a difference between the 68ec000 and the 68sec000? I have the latter in my Minimig and could do some tests.