Re: [Xenomai-help] rtserial interface stalls

[Jan Kiszka <jan.kiszka@domain.hid>]

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Vikesh Rambaran wrote:
> On Fri, 2009-03-20 at 12:46 +0100, Jan Kiszka wrote:
>> Vikesh Rambaran wrote:
>>> ...
>>> Alternative tried (after a bit of debugging)
>>> -----------------
>>>
>>> Changed  serialConfig.tx_timeout       = RTSER_DEF_TIMEOUT;
>>> to       serialConfig.tx_timeout       = RTDM_TIMEOUT_NONE;
>>>
>>> Task 2 then runs continuously. Writing to rtser0 returns valid number of
>>> bytes written but no data appears on serial port pin. At the same time
>>> rtser1 functions normally.
>> Without feedback from the device about its tx queue state you may
>> quickly overload it this way (definitely if written bytes > fifo length).
>>
> 
> The idea is to write data into the devices' circular buffer and return
> immediately. If there is not enough place in the buffer, i expected
> the write call to return an error code or fewer bytes than that which
> was requested. That would indicate a buffer overrun condition which can
> be flagged at application level. This way the task will not be delayed
> and other important functionality can be executed in a deterministic
> way.
> 
> The data transmitted on each serial channel is less than 150 bytes at
> 115200kb/s with the task having a fixed period of 20mS. This should not
> overflow default 4k buffers of the 16550A driver.
> 
> Well that's the plan:) Did i perhaps misunderstand the implementation
> for the tx_timeout ?
> 

No, I agree your approach is valid, and even non-blocking write should
behave as you expected. I actually forgot that the uart driver is that
smart - at least in theory. Something else is fishy.

When you switch to non-blocking, is there no data at all written, or
does transmission stop roughly around where blocking write would stop
the writer?

Jan


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