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.
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