From: [email protected]
To: [email protected]
Date: Thu, 4 Jul 2013 13:40:10 +0000
Subject: [meta-freescale] serial port timeout before expected # of bytes
arrives
Hello everyone,
I am trying to port an application that is receiving/sending data through the
serial port.
On the sabrelite board that is the /dev/ttymxc0 port, ie the 2ndary serial port
(the primary being /dev/ttymxc1).
I am using the functions select() and read() to read from the serial port , in
order to implement a timeout mechanism that is waiting for a few seconds for
bytes to arrive and if should they not arrive, then the timeout is reached.
The receiving loop works like this:
I wait for 2 bytes - the opcode of the command.Once I resolve a code, I wait
for 4 bytes designating the length of data that will follow (depending on the
command)I create a buffer in my application of size equal to the length I
received above.I start receiving the data.
Note that I have implemented reception of the data in 2 ways (since the 1st way
used to work, it was tried as is. Then, I tried the next as well):
a)receive my data using a for loop, reading() one byte at time. until all the
expected bytes arrive , or a timeout is reached.
b)receive my data using a while loop where I ask for all the remaining bytes to
be read(). Read() returns how many bytes have actually arrived, so I update the
remaining Bytes and re-read(). Again if a select() times-out without any data
arriving, the loop will exit.
Now, my problem is that while applications seem to be using this port without
any problem (f.e. minicom, rx, cat /dev/ttymxc0, echo "something" >
/dev/ttymxc0 ) , through the application I get timeouts for any file that is
bigger than 3-4kBytes.
Say I am trying to send a file 138kB. I may fail at byte ~40k, ~56k, or even
~12k. This is very weird. And I don't know what to assume is going wrong. Slow
processing on the local end seems to not be a problem, as I can read (in (b)
above) approx 58 bytes in the beginning and then 1 byte at a time. Could it be
the memory buffer? If yes, how can I increase its size? Could another
application be interfering with /dev/ttymxc0?
I am running fsl-image-test with all -dev, -sdk & -dbg options enabled.
Thank you for your help.
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