Messages in this thread | | | Date | Thu, 22 Mar 2001 19:21:28 +0100 | From | Geir Thomassen <> | Subject | Serial port latency |
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Hi.
My program controls a device (a programmer for microcontrollers) via the serial port. The program sits in a tight loop, writing a few (typical 6) bytes to the port, and waits for a few (typ. two) bytes to be returned from the programmer.
The program works, but it is very slow. I use an oscilloscope to monitor the serial lines, and notices that there is a large delay between the returned data, and the next new command. I really don't know if the delay is on the sending or the receiving side (or both).
This is what the program does:
fd=open("/dev/ttyS0",O_NOCTTY | O_RDWR);
tcsetattr(fd,TCSANOW, &tio); /* setting baud, parity, raw mode, etc */
while() { write( 6 bytes); /* send command */ read( 2 bytes); /* wait for reply */ }
The device on the serial port responds in typ. 10 ms, but the software uses over 500ms to get the reply and send the next command. Why is this happening ? I have a feeling that there is something obvious I am missing (like line buffering, but that's a stdio (libc) thing, isn't it ?).
BTW, I am running a 2.2 kernel ....
Geir, geirt@powertech.no - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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