Use Serial 1 or 2 RTS as GPIO on pixhawk 2.1 Cube

barchstien · October 2, 2019, 8:15pm

Hello Everyone

I am wondering if I can use the CTS or RTS of one of the telemetry serial (1 or 2) as a GPIO
My goal is to use this GPIO as an interrupt that will be triggered from the companion computer, to synchronize the companion computer to Ardupilot clock (the companion computer knows when the trigger is set as it its the source, a custom Ardupilot library will take a timestamp on the trigger, and insert the timestamp in a custom Mavlink message)

I have looked at the uC datasheet, and it looks possible HW wise

page 1003, chapter 30.3.14 Hardware flow control, it says :
“RTS and CTS flow control can be enabled independently by writing respectively RTSE and CTSE bits to 1 (in the USART_CR3 register).”

Then I looked at Ardupilot HW define files, particularly :

github.com

ArduPilot/ardupilot/blob/master/libraries/AP_HAL_ChibiOS/hwdef/fmuv3/hwdef.dat

# hw definition file for processing by chibios_hwdef.py
# for FMUv3 hardware (ie. for Pixhawk1, Pixhawk2 cube, XUAV2.1 etc)

# This hwdef.dat file contains a lot of comments so it can act as a
# reference for developers adding new boards.

# The hwdef.dat file defines all the hardware peripherals and pins for
# a port of ArduPilot to a board using the ChibiOS HAL. You should be
# able to write the hwdef.dat file for a new board with just the
# schematic for the board.

# This file is processed by chibios_hwdef.py to create hwdef.h for
# this board. You may find it useful to run chibios_hwdef.py manually
# when building this file for a new board. The resulting hwdef.h file
# is formatted to make it quite readable. It is strongly suggested
# that you read the resulting hwdef.h file when porting to a new board
# to make sure it has resulted in what you want.

# You should read this file in conjunction with the schematic for your
# board, the datasheet for the MCU for your board and the python

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github.com

ArduPilot/ardupilot/blob/master/libraries/AP_HAL_ChibiOS/hwdef/scripts/STM32F427xx.py

#!/usr/bin/env python
'''
these tables are generated from the STM32 datasheets for the
STM32F42x
'''

# additional build information for ChibiOS
build = {
    "CHIBIOS_STARTUP_MK"  : "os/common/startup/ARMCMx/compilers/GCC/mk/startup_stm32f4xx.mk",
    "CHIBIOS_PLATFORM_MK" : "os/hal/ports/STM32/STM32F4xx/platform.mk"
    }

# MCU parameters
mcu = {
    # location of MCU serial number
    'UDID_START' : 0x1FFF7A10,

    # ram map, as list of (address, size-kb, flags)
    # flags of 1 means DMA-capable
    # flags of 2 means faster memory for CPU intensive work

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There are :
“PA12:USART1_RTS” : 7,
“PA1:USART2_RTS” : 7,

Then I grep for the use of attach_interrupt, and I found
RCOutput::serial_read_bytes(…)

What I do not get, is what should I use as a pin number in the AP_HAL::GPIO class (in my very case ChibiOS::GPIO) ?
Can I use PA12 or PA1 with AltFunction_map ? In conjunction with DMA_Map ?