e Try if stty -F /dev/ttySx raw low_latency helps, no guarantees though On a PC, you can go hardcore and talk to standard serial ports directly, issue setserial /dev/ttySx uart none to unbind linux driver from serial port hw and control the port via inb/outb to port registers.. You should be able to do same on the arm device side, may be much harder on exotic serial port hw.. I've tried that, it works great The downside is you don't get interrupts when data arrives and you have to poll the register.
You want to make sure that VTIME is zero so that an inter-character timer never kicks in.. A major improvement has been the enlargement of the buffer size of the serial port from 1-byte.. But it seemed like it had no effect Are there any other things I can try to reduce latency? Since I control all devices it would even be possible to patch the kernel, but its preferred not to.. (see Serial-HOWTO for Program in Linux for the serial port When I use the serial port in Windows XP on a Linux host, I miss characters during.. Having talked to to some more engineers about the topic I came to the conclusion that this problem is not solvable in user space.
increase serial port buffer size linux
increase serial port buffer size linux
What IO interfaces will give me the lowest latency: select, poll, epoll or polling by hand with ioctl? Does blocking or non blocking IO impact latency?I tried setting the low_latency flag with setserial.. A quick hackfix would be increasing the buffer size to an appropruate I'm implementing a protocol over serial ports on Linux.. Since we need to cross the bridge into kernel land, we plan to implement an kernel module which talks our protocol and gives us latencies.
Try replacing the serial stream with a socket from another userspace process and see if the latencies improve.. You need to make sure the serial port is in raw mode (so you do 'noncanonical reads') and that VMIN and VTIME are set correctly.. I would probably start with setting VMIN to 1 and tune from there. At those line speeds you should not be seeing latencies that large, regardless of how you check for readiness.. None of those system calls have an effect on latency If you want to read and write one byte as fast as possible from userspace, you really aren't going to do better than a simple read()/write() pair.. ---- Edit ---- The serial controller uses is an 16550A Serial ports on linux are 'wrapped' into unix-style terminal constructs, which hits you with 1 tick lag, i. e828bfe731