[PATCH 1/1] LEON3: UT699 and GR712 sleep-mode d-cache fix

[Daniel Cederman]

On 2014-03-31 12:26, Sebastian Huber wrote:
> On 2014-03-31 12:17, Daniel Cederman wrote:
>> Branch always is a special case in which the ",a" causes the delay
>> instruction
>> to not be executed. From the Sparc architecture manual:
>>
>> "However, a bit in the delayed control-transfer instruction can cause
>> the delay
>> instruction to be annulled (that is, to have no effect) if the branch
>> is not
>> taken (or in the branch always case, if the branch is
>> taken)."
>
> Ok, I didn't have this "(or in the branch always case, if the branch is
> taken)" in my documentation.
>
>>
>> So I think it should be safe to remove the nop instruction.
>
> Since nobody knows which instruction will be after "ba,a" I think we
> should keep the nop.
>

According to our hardware guys that should not be a problem. But we can 
keep the nop for peace of mind.

>>
>> On 2014-03-31 12:03, Sebastian Huber wrote:
>>> On 2014-03-31 11:48, Daniel Cederman wrote:
>>>> See errata of respective chip. Some code-cleanup as well.
>>>> ---
>>>>   c/src/lib/libbsp/sparc/leon3/startup/bspidle.S |    7 ++-----
>>>>   1 file changed, 2 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/c/src/lib/libbsp/sparc/leon3/startup/bspidle.S
>>>> b/c/src/lib/libbsp/sparc/leon3/startup/bspidle.S
>>>> index 714d4e5..0924658 100644
>>>> --- a/c/src/lib/libbsp/sparc/leon3/startup/bspidle.S
>>>> +++ b/c/src/lib/libbsp/sparc/leon3/startup/bspidle.S
>>>> @@ -23,8 +23,5 @@
>>>>   SYM(bsp_idle_thread):
>>>>   SYM(leon3_power_down_loop):
>>>>   pwdloop:  mov   %g0, %asr19
>>>> -          ba    pwdloop
>>>> -          nop
>>>> -          retl
>>>> -          nop
>>>> -
>>>> +          lda   [%sp] 1, %g0            ! Needed for UT699 and GR712
>>>> +          ba,a    pwdloop
>>>>
>>>
>>> If I understand this ",a" notation correctly, then the instruction
>>> following the branch is not executed in case the branch is not taken.
>>> Since we branch always, this ",a" seems to be superfluous.  Is it safe
>>> to remove the nop instruction in the delay slot here?
>>>
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>
>