[U-Boot] [RFC][Timer API] Revised Specification - Implementation details

[Scott McNutt <smcnutt@psyent.com>]

J. William Campbell wrote:
> On 5/27/2011 6:07 AM, Scott McNutt wrote:
>> Graeme Russ wrote:
>>> Hi Wolfgang
>>>
>>> On Friday, May 27, 2011, Wolfgang Denk <wd@denx.de> wrote:
>>>> Dear Graeme Russ,
>>>>
>>>> In message <BANLkTik2SUm4Sm8aLjCrCmz+kcMGWgEzKw@mail.gmail.com> you 
>>>> wrote:
>>>>> Besides, Nios can return an increment of 10 (presumably ms) between
>>>>> two immediately consecutive calls. This causes early timeouts in CFI
>>>>> driver
>>>> Now this in turn is a bug in the timer implementation that needs to be
>>>> fixed.
>>
>> And this is what reset_timer() corrected.
>>
>>> Agreed, but that is not something I can achieve - I don't want to hold
>>> up this whole show that we have all put so much effort into for the
>>> sake of one weak function
>>
>> And I don't want to see something that currently works become broken
>> because we "improved" a feature ... simply because the resolution of
>> the timestamp is 10 msec rather than 1 msec.
>>
>> And just to be clear. This is not a Nios issue. Currently, if the
>> timestamp is incremented via a fixed period interrupt, and the period
>> of the interrupt is longer that 1 msec, calls to get_timer() may
>> produce early timeouts ... regardless of platform.
<snip>
> This can be 
> fixed in get_timer, making the 8 ms delay  become a minimum of 10 ms at 
> the expense of it becoming up to 20 ms sometimes.

Ok. Now I get it. Thanks.

<snip>
> This reset approach is bad in that it prevents 
> proper nesting of timing loops.

In my particular case, because reset_timer() resets the timestamp
to zero rather than simply restarting the timer. I believe leaving
the timestamp alone would solve the nesting problem.

<snip>
> The other fix 
> is in my opinion nicer, because it affects the nest loops less. If the 
> inner loop is executed 100 times, with the reset, the outer loop timeout 
> is extended by up to 1000 ms.

Bill, thank you for explaining -- probably for the nth time -- but it
did finally sink in.

Regards,
--Scott