How to use RX pin only in UART and TWAI?

[johansa]

When using UART and TWAI the API wants both RX and TX pin be set to something. I only need to listen so TX pins is not needed.
I want to save those pins for something else and I don't want the API to configure TX pins of UART and TWAI.

How to use RX pin only without TX pins in UART and TWAI?

[ESP_Sprite]

Generally for ESP-IDF drivers, you can pass '-1' as a GPIO not to assign anything. Alternatively, just select any existing GPIO, then after the driver is initialized, configure the GPIO to be something else.

[johansa]

Generally for ESP-IDF drivers, you can pass '-1' as a GPIO not to assign anything. Alternatively, just select any existing GPIO, then after the driver is initialized, configure the GPIO to be something else.

I'm testing on ESP32C3 and I get this when I have:

Code: Select all

static const twai_general_config_t g_config = {.mode = TWAI_MODE_LISTEN_ONLY,
.tx_io = -1,
.rx_io = 7,
.clkout_io = TWAI_IO_UNUSED,
.bus_off_io = TWAI_IO_UNUSED,
.tx_queue_len = 0,
.rx_queue_len = 5,
.alerts_enabled = TWAI_ALERT_NONE,
.clkout_divider = 0};

Code: Select all

expression: twai_driver_install(&g_config, &t_config, &f_config)

abort() was called at PC 0x40385307 on core 0
Core  0 register dump:
MEPC    : 0x4038085a  RA      : 0x40385312  SP      : 0x3fc91b70  GP      : 0x3fc8e400  
TP      : 0x3fc91c70  T0      : 0x37363534  T1      : 0x7271706f  T2      : 0x33323130  
S0/FP   : 0x00000004  S1      : 0x3fc91bd4  A0      : 0x3fc91b9c  A1      : 0x3fc91bd2  
A2      : 0x00000000  A3      : 0x3fc91bc9  A4      : 0x00000001  A5      : 0x3fc90000  
A6      : 0x7a797877  A7      : 0x76757473  S2      : 0x00000000  S3      : 0x00000000  
S4      : 0x00000000  S5      : 0x00000000  S6      : 0x00000000  S7      : 0x00000000  
S8      : 0x00000000  S9      : 0x00000000  S10     : 0x00000000  S11     : 0x00000000  
T3      : 0x6e6d6c6b  T4      : 0x6a696867  T5      : 0x66656463  T6      : 0x62613938  
MSTATUS : 0x00001881  MTVEC   : 0x40380001  MCAUSE  : 0x00000007  MTVAL   : 0x00000000  
MHARTID : 0x00000000

[ESP_Sprite]

Ah, I guess TWAI has its own define for that. You can try passing TWAI_IO_UNUSED.
If not, as I said, just use a random GPIO and re-initialize it for some other purpose later.