Re: [Xenomai-help] clock problem

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 08/08/2011 06:44 PM, Philip Ha wrote:
>> Hi Gilles,
>>
>> Sorry for the formatting, I am new to mailing lists.
>>
>> I have looked at the latency in the 16550A driver. The first thing 
>> the driver does in its ISR is to call rtdm_clock_read and store the 
>> resulting timestamp in a "struct rtser_event". The code I posted 
>> grabs this structure. If I use this as my timestamp I get the exact
>> same timing results.
> 
>>> are you sure that the interrupt triggers as soon as you receive a
>>> character, and not upon timeout when not receiving characters for some
>>> time? After all, 100us is approximately the time to transmit one
>>> character at 115200 bauds on the serial line.
>>>
>>> -- 
>>>                                           Gilles.
> 
> Hi Gilles,
> 
> I am not sending characters, I am sending a pulse from a 
> function generator into the DSR pin and looking for the rising
> edge event ( RTSER_EVENT_MODEMHI ). Any latency in the system
> should be similar for every pulse it receives, therefore the
> time between pulses should still be 1000000us.

The question remains: are you sure the UART does not introduce the
delay, have you checked the datasheet?

-- 
                                                                Gilles.