On Tue, Apr 24, 2012 at 3:50 PM, Jonas Bonn <[email protected]> wrote:
>
> On Tue, 2012-04-24 at 15:35 +0200, Peter Gavin wrote:
>> On Mon, Apr 23, 2012 at 11:19 AM, Julius Baxter <[email protected]>
>> wrote:
>> > Sure (by the way I would hope we can maintain a single compiler port
>> > and just pass a -mno-delay-slots or something, which should have a
>> > multilib option) but I'm just saying we would also need to have it
>> > detectable by software.
>>
>> Ok, so I'm going merge my no-delay-slot version with the main version.
>> I previously had it completely separate from the regular or1k code.
>>
>> Right now my plan is to add another bit called ND to the SR register.
>> I suppose bit 17 isn't currently taken, so I'll use that one. SR[ND]
>> will be zero for cores like the OR1200 that have a delay slot, and 1
>> for my core that doesn't have it.
>
> I don't see why this is needed. I need to know this at compile time...
> why do I need to know it at runtime?
It's not really for run-time, but to dump out the machine specs if
you're not sure what HW you have (or in our case, even more likely,
which config you synthesised into your FPGA from a few months ago?!?!)
>
>>
>> I'll add 3 mode flags to gcc, -mbranch-delay, -mno-branch-delay, and
>> -mcompat-branch-delay. -mbranch-delay will be the default for the
>> or1k arch. -mno-branch-delay will be the default for the or1knd arch.
>> -mcompat-branch-delay will work on either arch, and will just fill
>> all the delay slots with nops.
>
> Call it or2k and add -mcpu={or1k|or2k} flag. Then make main
> architecture 'openrisc' with:
>
> openrisc defaults to -mcompat-branch-delay
> or1k defaults to -mbranch-delay
> or2k defaults to -mno-branch-delay
The idea is to incrementally develop OR1K, and allowing us a nice
break for or2k to get things right(er) from the beginning. Extension
feature-set numbers might be more suitable in this case? OR1K1, OR1K2,
OR1K3, etc.?
Julius
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