Support low latency mode

[serialport]

Support low latency mode

[michaellass]

We needed this functionality as well and created a separate small crate for it: https://github.com/pc2/serialport_low_latency. It uses the TIOCGSERIAL and TIOCSSERIAL ioctls to change the serial line information and enable or disable low latency mode. This is basically the same as a setserial /dev/tty... low_latency would do.

It would be nice to incorporate this functionality directly into this crate. The reason why we haven't patched this into serialport-rs is portability and the necessity to run bindgen during build:

• The numbers for the ioctls differ between CPU architectures. Hence, we are currently using bindgen on <asm/ioctls.h> to determine the correct values.
• serialport-rs is cross-platform. I have no idea how to enable/disable the low latency mode on other Unixes or Windows.

Note that, if you have root permissions, it should also be possible to just write 1 into /sys/bus/usb-serial/devices/tty.../latency_timer. However, that file is typically writable only for root while the ioctls work for whoever can write to the tty device.