Assuming this is a binary data stream, this sounds like a classic VMIN/VTIME
issue on the read. I would try adjusting the read and VMIN to max packet
size and VTIME to 50% of the transmission interval to read packets. If the
interval is not known, you have to set it higher than the max
inter-character delay time allowed by the senderThe only option I know is to
do 1 char reads and do the packet assembly and checking yourself.
> -----Original Message-----
> From: Jean-Marie Bussat [SMTP:[EMAIL PROTECTED]]
> Sent: Thursday, May 18, 2000 4:48 AM
> To: [EMAIL PROTECTED]
> Subject: Reading to serial ports
>
>
> Hello,
>
> I would like to read data comming from two serial port as soon
> as they arrive.
>
> I have two devices, one connected to each port. They are sending
> data packets sequentially. E.g. device A send one packet then
> device B send its packet and so on. Packets can have any length
> going from 1 to 30 bytes.
> The serial lines have a speed of 4800 baud and packets are
> roughly sent every second.
>
> I would like to read packet as they are sent and I want to see
> them in the same order they were sent.
>
> Currently, I've written a C program which make use of "select"
> to achieve that. The problem is that it is not working in all
> conditions.
> If packets contain less than 2 bytes and if they arrive slowly,
> this is working well. But, if I set the packet sending speed
> to one every second, it seems to me that what I'm reading is
> only related to the size of the receiving fifo. I'm seeing
> packets but they are broken :
>
> data from device A | data from device B
> --------------------------------------------
> <packet 1A> | \
> | <packet 1B> |what I expect and
> <packet 2A> | |would like to see
> | <packet 2B> /
>
> ============================================
>
> <begining of | \
> packet 1A> | |
> | <packet 1B> |
> <end of 1A + | |what I'm getting
> begining of 2A> | |
> | <begining of 2B> |
> <end of 2A> | |
> | <end of 2B> /
>
> I've read in the serial-HOWTO that "select" might not be the
> most appropriate function to use but I have no idea of another
> alternative (I'm writing programs from time to time when it is
> required by my job but this is not my primary occupation - so,
> I'm lacking some knowledge about the programming API of the
> Linux kernel).
>
> Does anybody have an idea about how to do what seemed to me
> a simple task (at the begining) ? Or does anybody have any
> pointer/links to something that should do this job ?
>
> Thanks in advance for any answer.
> Best regards,
> Jean-Marie
> --
> +------------------------------------------------------------+
> | Jean-Marie Bussat - Dept. of physics, Princeton University |
> | CERN/EP - Bldg. 15-S-012 - CH-1211 GENEVA 23 - Switzerland |
> | Email: [EMAIL PROTECTED] |
> | Tel: (41 22) 767 32 41 Fax: (41 22) 767 32 41 |
> +------------------------------------------------------------+
>
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