Hi Alan, Op 19 april 2012 13:19 heeft Alan Cox <alan@xxxxxxxxxxxxxxx> het volgende geschreven: >> We are wondering if it is possible to give the TTY device in more >> deterministic behavior (as in "less locks & no sleeping") >> So in case of non blocking read/write behavior: >> - We want directly write data to the serial_core transmit buffer and >> return immediately. > > If you have the tty in raw mode then that is basically what the ldisc > code does (plus any flow control you may have selected). > >> - Incoming data should be buffered, on a read data is read directly >> from that buffer and when no data available return immediately > > Ditto in raw mode, and you can use O_NDELAY or the VMIN/VTIME fields to > optimise block transfer behaviour. We do actually do an additional > memcpy but memory copies of cached memory are so cheap it should be > irrelevant unless trying to do megabit speeds on low end embedded > processors. > I assume we use raw mode: - We call the cfmakeraw() function. - We also set the O_NDELAY flag, VMIN = 1, VTIME = 0 >> We have the idea that the default N_TTY line discipline introduces too > > Based upon what analysis ? > I think you are right: I did not yet do "real" analysis on the N_TTY line discipline apart from source code analysis. I will do some extra ftrace tests, to find out what causes the delays in the execution time. I'll come back to that... >> much overhead & locking behavior what makes it less suitable for >> deterministic serial communication on a PREEMT_RT platform. > > Are you using USB ports ? > No, it is a UART peripheral in a FPGA on our target board. We use a self written serial_core base driver > Alan Thanks, Ivo Sieben -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
