UART event queue full
Posted: Wed Jul 09, 2025 7:30 am
Hi everybody,
I'm using an ESP32 with IDF 5.4.1. I'm using all three serial ports: UART0 is for debug messages, UART1 is on an RS485 bus, and UART2 receives command. I'm mostly concerned about UART1 on the 485 mode.
I configure it quite simply:
Then I put the queues into a set:
and then I have a task that blocks xQueueSelectFromSet, and responds to the event UART_DATA by putting the data into a ring buffer for further processing.
All is good and dandy, except if I unplug my serial adapter. If I try to transmit (no rx! only tx) on UART1 I start to get
But there is nothing connected to my RX pin! Why am I getting this message? There should be nothing to receive at this point. Also, the UART_BREAK starts to get triggered.
So I thought about an electrical problem, maybe the floating pin is picking up data (!!)? But then, why don't I get UART_DATA events?
Also, once the "UART event queue full" message appears, I cannot properly write to the other two serials too, any communication attempt results in more "UART event queue full". So I modified uart.c to at least tell me which serial and what event:
(this is the message at line 1303. BTW shouldn't this be an ERROR log??) uart_event.type is always 0 (UART_DATA), and I get a message for each uart. But why don't I see my UART_DATA event in the event loop? If I wait a couple minutes to "cool off", and send data, I finally get some timid UART_DATAs, but then the systems reverts to "UART event queue full" until I reset.
So I tried switching off UART_MODE_RS485_HALF_DUPLEX and doing the RE-giggling by hand. Not optimal, but it works. In this modality I never get "UART event queue full" so I suspect there is something wonky happening when UART_MODE_RS485_HALF_DUPLEX is set. I tried the other two options: UART_MODE_RS485_COLLISION_DETECT and UART_MODE_RS485_APP_CTRL and the "UART event queue full" message disappears, but I get an enormous number of UART_BREAK events (also, I don't want collision detection or any mode where the header file says "(used for test purposes)").
Obviously I'm not going to use the serial port without the 485 transceiver connected, but I would also expect the system not to react into this destructive way, which to me is inexplicable.
I'm using an ESP32 with IDF 5.4.1. I'm using all three serial ports: UART0 is for debug messages, UART1 is on an RS485 bus, and UART2 receives command. I'm mostly concerned about UART1 on the 485 mode.
I configure it quite simply:
Code: Select all
uart_config_t poor_uart_config = {
.baud_rate = 500000,
.data_bits = UART_DATA_8_BITS,
.parity = UART_PARITY_DISABLE,
.stop_bits = UART_STOP_BITS_1,
.flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
.source_clk = UART_SCLK_DEFAULT,
};
//Install POOR_UART_NUM driver, and get the queue.
uart_driver_install(1, BUF_SIZE, 2048, 20, &my_queue, 0);
uart_param_config(1, &poor_uart_config);
uart_set_pin(17, 18, poor_rx, 27, UART_PIN_NO_CHANGE);
uart_set_mode(1, UART_MODE_RS485_HALF_DUPLEX);
Code: Select all
serial_queues = xQueueCreateSet(48);
xQueueAddToSet(my_queue, serial_queues);
xQueueAddToSet(my_queue2, serial_queues);
All is good and dandy, except if I unplug my serial adapter. If I try to transmit (no rx! only tx) on UART1 I start to get
Code: Select all
UART event queue full
UART event queue full
UART event queue full
UART event queue full
So I thought about an electrical problem, maybe the floating pin is picking up data (!!)? But then, why don't I get UART_DATA events?
Also, once the "UART event queue full" message appears, I cannot properly write to the other two serials too, any communication attempt results in more "UART event queue full". So I modified uart.c to at least tell me which serial and what event:
Code: Select all
ESP_EARLY_LOGV(UART_TAG, "UART event queue full B %d nr %d", uart_event.type, uart_num);
So I tried switching off UART_MODE_RS485_HALF_DUPLEX and doing the RE-giggling by hand. Not optimal, but it works. In this modality I never get "UART event queue full" so I suspect there is something wonky happening when UART_MODE_RS485_HALF_DUPLEX is set. I tried the other two options: UART_MODE_RS485_COLLISION_DETECT and UART_MODE_RS485_APP_CTRL and the "UART event queue full" message disappears, but I get an enormous number of UART_BREAK events (also, I don't want collision detection or any mode where the header file says "(used for test purposes)").
Obviously I'm not going to use the serial port without the 485 transceiver connected, but I would also expect the system not to react into this destructive way, which to me is inexplicable.