On Thu, May 5, 2022 at 7:47 AM C Smith via Xenomai <xenomai@xenomai.org> wrote: > > In my serial_config which I pass to the ioctl() that sets up my > 16550A.ko serial port > I have set .rx_timeout = 500000 > and I am doing non-blocking reads. > > This indeed results in a 500us delay when reading a serial port with > no incoming bytes, which I can measure precisely on an oscilloscope (I > have a DIO port pulse depicting the duration of the read()). > > This is wasted time in my (RT userspace) app during the read() when > there is no serial traffic on a particular port, and I have many > serial ports. But why must I decide how long to stall the RT process > with a timeout? Can't read() return immediately if there is no data in > the device ? > > Must I use an ioctl with RTSER_RTIOC_GET_STATUS to inspect the UART > LSR for data available? > > (This is a RT userspace app on Xeno 3.1.2, kernel 4.19.229, intel I5, > 16550 compat UART)
IIRC as soon you configure a timeout, reads are blocking. Configuring -1 as timeout will cause read to return immediately with -EAGAIN if no data is available. -- Thanks, //richard
