idf-twai-optimization.txt

twai_self_test failure with CONFIG_COMPILER_OPTIMIZATION_SIZE=y

Software version used: esp-idf v4.3-dev-1561-g357a27760
    (problem also affects v4.2-dev-2968-g8bc19ba89 (circuitpython 6.0.0-rc.0))

Hardware used: ESP32-S2-Kaluga-1

Teseting procedure:
  1. Prepare hardware: Install jumper wire between pins 17 and 18.
  2. Build working configuration:
        cd examples/peripherals/twai/twai_self_test/
        git clean -dxf
        idf.py set-target esp32-s2
        idf.py menuconfig

            In "Example Configuration" set
                TX GPIO number to 17
                RX GPIO number to 18
            save and exit

        idf.py flash

        Open terminal, press reset button.

        Result: Test succeeds, printing many "Msg received" log lines and finally "Driver uninstalled"


  3. Build non-working configuration:
        idf.py menuconfig
            
            In "Compiler options" set
                Optimization Level to "Optimize for size (-Os)"
            save and exit

        idf.py flash

        Open terminal, press reset button.

        Result: Test fails, hanging after printing "TWAI Self Test: Driver started"


Note: With additional instrumentation added, it appears that when the
compiler optimization is "-Os", writes to acceptance_filter.acr and .amr
do not succeed, and incorrect values are read back.

Patch to add instrumentation: https://gist.github.com/1c90b383888ca40f3dbafd0b4d68ce9d

Typical instrumentation output when working properly:

I (325) TWAI Self Test: Driver installed
I (325) TWAI Self Test: f_config.acceptance_code = 0x00000000
I (335) TWAI Self Test: f_config.acceptance_mask = 0xffffffff
I (345) TWAI Self Test: f_config.single_filter = 0x00000001
I (345) TWAI Self Test: mode_reg = 0x0000000b
I (355) TWAI Self Test: command_reg = 0x00000000
I (355) TWAI Self Test: status_reg = 0x0000003c
I (365) TWAI Self Test: clock_divider_reg = 0x00000300
I (375) TWAI Self Test: acceptance_filter.acr[] =
I (375) TWAI Self Test:  00
I (375) TWAI Self Test:  00
I (385) TWAI Self Test:  00
I (385) TWAI Self Test:  00
I (395) TWAI Self Test: 

I (395) TWAI Self Test: acceptance_filter.amr[] =
I (395) TWAI Self Test:  ff
I (405) TWAI Self Test:  ff
I (405) TWAI Self Test:  ff
I (405) TWAI Self Test:  ff
I (415) TWAI Self Test: 


Typical instrumentation output when working improperly ("Optimize for size") - note incorrect values read back for acceptance_filter:

I (328) TWAI Self Test: Driver installed
I (328) TWAI Self Test: f_config.acceptance_code = 0x00000000
I (338) TWAI Self Test: f_config.acceptance_mask = 0xffffffff
I (348) TWAI Self Test: f_config.single_filter = 0x00000001
I (348) TWAI Self Test: mode_reg = 0x0000000b
I (358) TWAI Self Test: command_reg = 0x00000000
I (358) TWAI Self Test: status_reg = 0x0000003c
I (368) TWAI Self Test: clock_divider_reg = 0x00000300
I (378) TWAI Self Test: acceptance_filter.acr[] =
I (378) TWAI Self Test:  db
I (378) TWAI Self Test:  ff
I (388) TWAI Self Test:  0d
I (388) TWAI Self Test:  7f
I (398) TWAI Self Test: 

I (398) TWAI Self Test: acceptance_filter.amr[] =
I (398) TWAI Self Test:  7e
I (408) TWAI Self Test:  77
I (408) TWAI Self Test:  fe
I (408) TWAI Self Test:  da
I (418) TWAI Self Test: