Espressif ESP32-S2 User Manual

Chapter 2. API Reference
esp_err_t uart_set_tx_empty_threshold(uart_port_t uart_num, int threshold)
Set uart threshold values for TX fifo empty.
Return
• ESP_OK Success
• ESP_ERR_INVALID_ARG Parameter error
• ESP_ERR_INVALID_STATE Driver is not installed
Parameters
• uart_num: UART_NUM_0, UART_NUM_1 or UART_NUM_2
• threshold: Threshold value below which TX fifo empty interrupt is generated
esp_err_t uart_set_rx_timeout(uart_port_t uart_num, const uint8_t tout_thresh)
UART set threshold timeout for TOUT feature.
Return
• ESP_OK Success
• ESP_ERR_INVALID_ARG Parameter error
• ESP_ERR_INVALID_STATE Driver is not installed
Parameters
• uart_num: Uart number to configure, the max port number is (UART_NUM_MAX -1).
• tout_thresh: This parameter defines timeout threshold in uart symbol periods. The maximum
value of threshold is 126. tout_thresh = 1, defines TOUT interrupt timeout equal to transmission time
of one symbol (~11 bit) on current baudrate. If the time is expired the UART_RXFIFO_TOUT_INT
interrupt is triggered. If tout_thresh == 0, the TOUT feature is disabled.
esp_err_t uart_get_collision_flag(uart_port_t uart_num, bool *collision_flag)
Returns collision detection flag for RS485 mode Function returns the collision detection flag into variable
pointed by collision_flag. *collision_flag = true, if collision detected else it is equal to false. This function
should be executed when actual transmission is completed (after uart_write_bytes()).
Return
• ESP_OK Success
• ESP_ERR_INVALID_ARG Parameter error
Parameters
• uart_num: Uart number to configure the max port number is (UART_NUM_MAX -1).
• collision_flag: Pointer to variable of type bool to return collision flag.
esp_err_t uart_set_wakeup_threshold(uart_port_t uart_num, int wakeup_threshold)
Set the number of RX pin signal edges for light sleep wakeup.
UART can be used to wake up the system from light sleep. This feature works by counting the number of
positive edges on RX pin and comparing the count to the threshold. When the count exceeds the threshold,
system is woken up from light sleep. This function allows setting the threshold value.
Stop bit and parity bits (if enabled) also contribute to the number of edges. For example, letter ‘a’with
ASCII code 97 is encoded as 0100001101 on the wire (with 8n1 configuration), start and stop bits included.
This sequence has 3 positive edges (transitions from 0 to 1). Therefore, to wake up the system when ‘a’is
sent, set wakeup_threshold=3.
The character that triggers wakeup is not received by UART (i.e. it can not be obtained from UART FIFO).
Depending on the baud rate, a few characters after that will also not be received. Note that when the chip enters
and exits light sleep mode, APB frequency will be changing. To make sure that UART has correct baud rate
all the time, select REF_TICK as UART clock source, by setting use_ref_tick field in uart_config_t to true.
Note in ESP32, the wakeup signal can only be input via IO_MUX (i.e. GPIO3 should be configured as
function_1 to wake up UART0, GPIO9 should be configured as function_5 to wake up UART1), UART2
does not support light sleep wakeup feature.
Return
• ESP_OK on success
• ESP_ERR_INVALID_ARG if uart_num is incorrect or wakeup_threshold is outside of [3, 0x3ff]
range.
Parameters
• uart_num: UART number, the max port number is (UART_NUM_MAX -1).
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Release v4.4

Espressif ESP32-S2 Specifications

General

Brand	Espressif
Model	ESP32-S2
Category	Single board computers
Language	English