MQX Software SolutionsのトピックRe: select() on serial port

select() on serial port

pozz — Thu, 07 Feb 2013 11:23:51 GMT

I'm using MQX 4.0 with Tower system (Kinetis K60).

I'm writing a task that communicates to another device through the serial port of TWR-SER board. I'm able to open the port and send/receive bytes on that port without problems.

Now I'd like to have a function similar to the classical select() function: I want to put the task in blocked state until a character on the serial port has arrived or a timeout expires. I noticed the select() function is implemented only in RTCS, but not for simple I/O serial port.

The serial protocol I'm implemented is master/slave, where the MQX application is the master. So it sends a packet and waits for the answer. The wait can't be indefinitely, because the other device couldn't be actually connected, so I have to do something if this condition occurs.

I can open the serial port in polling non-blocking mode and poll the serial port with fgetc() and make some ticks calculations to detect the timeout:

while(1) {

send_packet();

end = start = _time_ticks();

while(_time_diff(end, start) < TIMEOUT) {

c = fgetc(serial_port);

if (c >= 0) {

add_to_rx(c);

if (rxpacket_complete()) {

break;

}

if (rxpacket_complete()) {

/* Process the incoming packet */

clear_rx();

} else {

/* No answer */

}

But I'd like to avoid this. The task is always running and never goes in blocked mode.

Re: select() on serial port

DavidS — Wed, 06 Mar 2013 17:54:31 GMT

Hi Giuseppe,

Please have a look at an example of timeout for a read() with timeout.

result_custom = read_custom(fh_ptr,(pointer)bptr,MAX_NUMER_OF_CHARACTERS,INPUT_CHARACTER_DELAY_MILLISECONDS); //DES read 7 character or timeout in X seconds

Not certain this addresses your needs totally but hopefully gets you moving in right direction.

Regards,

David

Re: select() on serial port

Monica — Tue, 19 Mar 2013 23:19:24 GMT

Giuseppe, is this working now?

Let us know :smileywink:

Regards!

Re: select() on serial port

pozz — Wed, 20 Mar 2013 07:40:58 GMT

I'm sorry, but I'm not working on that project now. When I come back to it, I will try the suggestion of David and let you know the result.