Re: [Qemu-devel] [Consult] About SPRs information

[Chen Gang]

On 4/29/15 21:32, Chen Gang wrote:
> On 4/29/15 05:43, Peter Maydell wrote:
>> On 28 April 2015 at 22:32, Chen Gang <address@hidden> wrote:
>>> The related information for cmpexch instruction:
>>>
>>>   Description
>>>
>>>     Compare the 8-byte contents of the CmpValue SPR with the 8-byte
>>>     value in memory at the address held in the first source register. If
>>>     the values are not equal, then no memory operation is performed. If
>>>     the values are equal, the 8-byte quantity from the second source
>>>     register is written into memory at the address held in the first
>>>     source register. In either case, the result of the instruc- tion is
>>>     the value read from memory. The compare and write to memory are
>>>     atomic and thus can be used for synchronization purposes. This
>>>     instruction only operates for addresses aligned to a 8-byte boundary.
>>>     Unaligned memory access causes an Unaligned Data Reference interrupt.
>>
>> I suggest you look at how existing CPUs handle this kind of
>> atomic operation.
>>

I finished cmpexch(), referenced to store_exclusive() in arm and alpha.
Hope what I have done is correct (I guess, it should be).

 - Save information about cmpexch (add additional variable in CPUState).

 - Generate an exception for it.

 - Process the related exception in main.c with start/end_exclusive()
   just like what alpha or arm has done.


Thanks.

> OK, thanks.
> 


>> I also suggest you stop adding implementations of *new* instructions
>> and concentrate on getting a basic set into shape for inclusion.
>> The more stuff you keep adding the bigger your patchset is going
>> to get and the harder it is going to get to review.
>>

Reconstruction the code is really very useful, cmp*, shl?add*, V?int_?.
That will not only simplify reading, but also speed up coding.

Thank you for your valuable suggestions again.

> 
> For me, current code is not quite much, and really easy enough. At
> present I am still going smoothly (the issues are mainly about
> understanding new instructions which I shall meet).
> 
> I still want to reach "display hello world" successfully (it does not
> seem quite difficult to me), then reconstruct current code, and send
> patch to upstream.
> 
> But sorry, it seems I can not finish it within this month (and I shall
> try to finish within next month).
> 
> 
> Thanks.
> 

-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed