Serial driver - abandon FIFO data on error?

Jim Granville wrote:
> Chris Carlen wrote:
>> Jim Granville wrote:
>>
>>> Chris Carlen wrote:
>>>
>>>>
>>>> What is typically done in UART drivers with the contents of the hw 
>>>> FIFO when an overrun is detected?
>>>
>>>
>>>  My understanding is that the better HW FIFO UART designs have a 
>>> 'wider fifo' that includes the error flags, for each byte. The errata 
>>> I have seen as well, indicates they do not always get the tracking of 
>>> those flags quite right!
>>>
>>>  So, I would say 'best practise' would be to implement a similar SW 
>>> scheme:
>>> slightly more work, but it gives much more info for fault anaylsis, and
>>> as you indicate, works better by discarding less data.
>>
>>
>> I'm not writing a software UART, just a software buffer extension of a 
>> hardware UART with 16-byte FIFO.  When an overrun error occurs, know 
>> that it occured after the 16 bytes in the FIFO.  Any other error (FE, 
>> PE) I have no idea to which character it pertains since it is possible 
>> that I don't get into the interrupt routine until several chars have 
>> been queued.  That is because the RX ISR will need to be preemptable 
>> by other much more time critical interrupts in a real-time controller.
> 
> So, this device has a HW CHAR fifo, but not an HW Flag/error fifo ?
> - seems to have not caught up with the better uart designs... ?


It took me a while to figure out the functionality of two bits in a 
register (the documentation can be a bit vacuous).

Indeed, the F2812 tracks framing and parity errors for each char in the 
FIFO.

There are two bits: SCIRXBUF.SCIFFFE and SCIFFPE which reflect the 
status of the character at the top of the FIFO (the one you are about to 
read from SCIRXBUF.RXDT).

There are also a set of error bits for FE, PE, etc., which just latch 
whenever an error is detected.  I had thought the SCIFFFE and SCIFFPE 
were redundant with these (and wondered why) until I figured out that 
these two track the error status of the top FIFO char.




-- 
Good day!

____________________________________
CRC
crobcREMOVETHIS@BOGUSsbcglobal.net
NOTE, delete texts: "REMOVETHIS" and
"BOGUS" from email address to reply.