Hi Ali,
Thanks for your help. I've fixed my problem now, it appears the the only
reason the two traces differed was because the instruction selected the
JsrAndLink when ZeroReg was 0, as the RA register is set to 0. However
having looked at the code for the JSR decode in alpha it appears we
differ a lot more than I was aware (our ISA is purportedly alpha-like).
Anyway moving onto another question. In our current simulation
environment we make calls through to the o/s using builtin functions,
much like the syscall functions in m5. For example when a JSR is
executed, if the value of register Rb has the top 16 bits set e.g.
0xffffxxxx then we call a builtin function such as fstat, fopen etc
defined by the xxxx part of the register.
What is the simplest way to do this. Is the value of a register
available to the decoder? e.g. can I look at the register index in, say
branch.isa, can I also look at the value of that register. I appreciate
this isn't feasible in hardware, but presumably syscalls are treated as
special cases.
currently I have:
format Jump {
0x15: jsr(IsCall);
}
so ideally I want to be able to do something like this:
format Jump {
0x15:
if(Rb & 0xffff0000 == 0xffff0000) {
syscall(Rb & 0x0000ffff);
}
else {
jsr(IsCall);
}
}
Ali Saidi wrote:
> Matt,
>
> I would still guess that it's something to do with a hardcoded value,
> if not in decoder.isa than in one of the other isa files. Here are
> some probable candidates:
> branch.isa: return (RA == 31)
> int.isa: if (RC == 31) {
> main.isa: if (RC == 31) {
> mem.isa: if (RA == 31) {
> mem.isa: if (RA != 31) {
>
> Ali
>
> On Aug 20, 2007, at 12:31 PM, Steve Reinhardt wrote:
>
>> Hi Matt,
>>
>> On 8/20/07, *Matthew James Horsnell* <[EMAIL PROTECTED]
>> <mailto:[EMAIL PROTECTED]>> wrote:
>>
>> Having followed Steve's suggestions I have debugged the the binaries
>> using gdb, and can indeed see that when ZeroReg is set to 31 (and
>> ReturnAddressReg is 0) then the code calls JsrAndLink, whereas
>> when the
>> constants are switched the code calls Jsr, but I have extensively
>> searched to see where I may have missed a constant.
>>
>>
>> If this is the case, then I suggest setting a breakpoint on
>> decodeInst() in decoder.cc and stepping through to see why when the
>> machine instruction is being decoded it is returning a Jsr object and
>> not a JsrAndLink object. That line I pointed out earlier in
>> branch.isa is what's supposed to control that, but obviously it's not
>> working...
>>
>> Steve
>>
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--
Matt Horsnell,
Advanced Processor Technologies Group,
University of Manchester.
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