libmavconn : enable low-latency mode on Linux #975
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TSC21
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Mar 15, 2018
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Some common USB-UART convertors like the FTDI accumulates individual bytes from the serial link in order to send them in a single USB packet (Nagling). This commit sets the ASYNC_LOW_LATENCY flag, which the FTDI kernel driver interprets as a request to drop the Nagling timer to 1ms (i.e send all accumulated bytes after 1ms.) This reduces average link RTT to under 5ms at 921600 baud, and enables the use of mavros in systems where low latency is required to get good performance for e.g estimation and controls.
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Yeah I read that. I was asking if you have some pratical example where you tested this (ex: VIO) and you could show us the improvement on that situation. |
vooon
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Mar 21, 2018
| @@ -61,7 +62,6 @@ MAVConnSerial::MAVConnSerial(uint8_t system_id, uint8_t component_id, | |||
| // Workaround to set some options for the port manually. This is done in | |||
| // Boost.ASIO, but until v1.12.0 (Boost 1.66) there was a bug which doesn't enable relevant | |||
| // code. Fixed by commit: https://github.com/boostorg/asio/commit/619cea4356 | |||
| int fd = serial_dev.native_handle(); | |||
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Some common USB-UART converters like the FTDI accumulate individual bytes from the serial link in order to send them in a single USB packet ("Nagling" - https://en.wikipedia.org/wiki/Nagle%27s_algorithm). This commit sets the ASYNC_LOW_LATENCY flag, which the FTDI kernel driver interprets as a request to drop the Nagling timer to 1ms (i.e send all accumulated bytes after 1ms.)
This reduces average link RTT to under 5ms at 921600 baud (it is 20-30 ms on master), and enables the use of mavros in systems where low latency is required to get good performance for e.g estimation and controls. As a side effect, this also greatly increases performance of timesync on serial links and prevents the hard-resets we've been seeing.