[U-Boot] [PATCH] common/xyzModem.c: Fix delay timeout calculation

[Stefan Roese]

Hi Andrew,

On 26.08.2016 15:40, Andrew F. Davis wrote:
> On 08/26/2016 12:18 AM, Stefan Roese wrote:
>> On 25.08.2016 20:43, Andrew F. Davis wrote:
>>> When waiting for input in CYGACC_COMM_IF_GETC_TIMEOUT we delay 2
>>> seconds by incrementing and checking a counter variable every 20
>>> uSeconds. The overhead in the loop calling tstc() millions of times
>>> causes the timeout to be closer to 20 seconds. Delay longer per iteration
>>> to reduce overhead and bring the timeout back closer to the correct time.
>>>
>>> Signed-off-by: Andrew F. Davis <afd at ti.com>
>>> ---
>>>  common/xyzModem.c | 5 ++---
>>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/common/xyzModem.c b/common/xyzModem.c
>>> index 5656aac..c3f2afc 100644
>>> --- a/common/xyzModem.c
>>> +++ b/common/xyzModem.c
>>> @@ -71,11 +71,10 @@ typedef int cyg_int32;
>>>  static int
>>>  CYGACC_COMM_IF_GETC_TIMEOUT (char chan, char *c)
>>>  {
>>> -#define DELAY 20
>>>    unsigned long counter = 0;
>>> -  while (!tstc () && (counter < xyzModem_CHAR_TIMEOUT * 1000 / DELAY))
>>> +  while (!tstc () && (counter < xyzModem_CHAR_TIMEOUT))
>>>      {
>>> -      udelay (DELAY);
>>> +      mdelay (1);
>
> Thinking about this more, all we have to change is to remove the "*
> 1000" and switch to mdelay. That's a smaller change and results in an
> even more correct timeout time.
>
>  CYGACC_COMM_IF_GETC_TIMEOUT (char chan, char *c)
>  {
>  #define DELAY 20
>  unsigned long counter = 0;
> -  while (!tstc () && (counter < xyzModem_CHAR_TIMEOUT * 1000 / DELAY))
> +  while (!tstc () && (counter < xyzModem_CHAR_TIMEOUT / DELAY))
>    {
> -      udelay (DELAY);
> +      mdelay (DELAY);
>        counter++;
>    }

Yes, this should also work and is a less intrusive change. But the
result is that the delay is at least 20ms each time. And the
original version had a much smaller delay here.

Even better would be if you change the loop to a timer based
timeout detection. Please grep for get_timer() to see some examples.

Thanks,
Stefan