SBUS on Linux: replace termios with termios2

[SalimTerryLi]

Describe problem solved by this pull request
Previous version of code could not set the serial device properly, which leads to incorrect read of _rcs_buf. This PR solves that problem.

Describe your solution
Code comes from existing drivers/linux_sbus, which works well.
A problem still exists that rc_input will report
ERROR [px4_work_queue] unknown serial port: /dev/ttyAMA0
for that customised ttyAMA0 is not defined which is necessary for function px4::serial_port_to_wq()

Test data / coverage

pxh> rc_input status
INFO  [rc_input] Running
INFO  [rc_input] Max update rate: 250 Hz
INFO  [rc_input] Serial device: /dev/ttyAMA0
INFO  [rc_input] RC scan state: SBUS, locked: yes
INFO  [rc_input] CRSF Telemetry: no
INFO  [rc_input] SBUS frame drops: 0
rc_input: cycle time: 6006 events, 81508us elapsed, 13.57us avg, min 8us max 89us 5.316us rms
rc_input: publish interval: 1600 events, 14997.50us avg, min 11937us max 19990us 1733.078us rms
 input_rc_s
	timestamp: 4067569737  (0.008766 seconds ago)
	timestamp_last_signal: 4067569737
	channel_count: 18
	rssi: 255
	rc_lost_frame_count: 0
	rc_total_frame_count: 0
	rc_ppm_frame_length: 0
	values: [1512, 1509, 1934, 1522, 1094, 1094, 1514, 1514, 1094, 1094, 1094, 1094, 944, 944, 1514, 1514, 998, 998]
	rc_failsafe: False
	rc_lost: False
	input_source: 9

[dagar]

A problem still exists that rc_input will report
ERROR [px4_work_queue] unknown serial port: /dev/ttyAMA0
for that customised ttyAMA0 is not defined which is necessary for function px4::serial_port_to_wq()

Feel free to add it here if you'd like - https://github.com/PX4/Firmware/blob/9d2a37b35d3af1f8848565ee8eedd6aa94a19251/platforms/common/px4_work_queue/WorkQueueManager.cpp#L166-L202

[dagar]

Could you structure the ifdef so that the decoder initialise section is run in both cases?

https://github.com/PX4/Firmware/blob/9d2a37b35d3af1f8848565ee8eedd6aa94a19251/src/lib/rc/sbus.cpp#L224-L229

[SalimTerryLi]

A problem still exists that rc_input will report
ERROR [px4_work_queue] unknown serial port: /dev/ttyAMA0
for that customised ttyAMA0 is not defined which is necessary for function px4::serial_port_to_wq()

Feel free to add it here if you'd like -

https://github.com/PX4/Firmware/blob/9d2a37b35d3af1f8848565ee8eedd6aa94a19251/platforms/common/px4_work_queue/WorkQueueManager.cpp#L166-L202

Is it OK to add something like ttyDEFAULT and wq_configurations::UART_DEFAULT? ttyAMA0 is pick up from my own board but it can be ttyUSB0 as well.

EDIT: Mostly like to remove that error and create some place for unrecognized UART instead of hp_default?

[dagar]

Is it OK to add something like ttyDEFAULT and wq_configurations::UART_DEFAULT? ttyAMA0 is pick up from my own board but it can be ttyUSB0 as well.

EDIT: Mostly like to remove that error and create some place for unrecognized UART instead of hp_default?

The point of it is to have a thread dedicated to each physical bus. At the moment it's all static, but it could be more flexible in the future (needs some thought and rework).

I would either:

1. Add a /dev/ttyAMA0, maybe behind a __PX4_LINUX define seems like the less bad option, unless you'd like to explore making the PX4 WQs more runtime configurable.
2. Make it UART_UNKNOWN instead of UART_CUSTOM