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driver: add rs485 half duplex interface support to uart driver (update after review)

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An existing UART driver does not support RS485 half duplex mode.
This task adds this functionality to ESP_IDF UART driver.
driver/uart.c/h: updated to add support of RS485 half duplex mode
examples/peripherals/uart_echo_rs485/main/rs485_example.c: added test example
components/driver/test/test_uart.c: added test of RS485 half duplex mode
docs/en/api-reference/peripherals/uart.rst: updated documentation
test_uart.c: suppress GCC warnings about discarded const qualifiers
uart.rst: remove sphinx warning - "Duplicate explicit target name"
simple change in uart.h file
update (test_uart.c) after rebase from master
update uart.rst, uart.c, rs485_example.c
Update example description in file Readme.md
update uart.c/h, uart.rst, test_uart.c according to review results
update uart.h (uart_set_rx_timeout() description
test_uart.c remove ignore tag
uart.c/h: fix param errors
test_uart.c: Remove GCC warning supress
uart.rst: fix the notes
rs485_example.c: fix output

The tests are completed using RS485 adapters hardware connected to two ESP32 WROVER KITs.

TW#13812
Closes https://github.com/espressif/esp-idf/pull/667
Closes https://github.com/espressif/esp-idf/pull/1006
This commit is contained in:
Alex Lisitsyn
2018-06-27 16:48:14 +02:00
parent 0ec81181b4
commit ef5dc73f6f
5 changed files with 45 additions and 43 deletions
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17
docs/en/api-reference/peripherals/uart.rst
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@@ -43,7 +43,7 @@ The alternate way is to configure specific parameters individually by calling de
Configuration example: ::
const int uart_num = UART_NUM_1;
const int uart_num = UART_NUM_2;
uart_config_t uart_config = {
.baud_rate = 115200,
.data_bits = UART_DATA_8_BITS,
@@ -68,8 +68,8 @@ In next step, after configuring communication parameters, we are setting physica
Instead of GPIO pin number we can enter a macro :cpp:type:`UART_PIN_NO_CHANGE` and the currently allocated pin will not be changed. The same macro should be entered if certain pin will not be used. ::
// Set UART pins(TX: IO16, RX: IO17, RTS: IO18, CTS: IO19)
ESP_ERROR_CHECK(uart_set_pin(uart_num, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE, 18, 19));
// Set UART pins(TX: IO16 (UART2 default), RX: IO17 (UART2 default), RTS: IO18, CTS: IO19)
ESP_ERROR_CHECK(uart_set_pin(UART_NUM_2, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE, 18, 19));
.. _uart-api-driver-installation:
@@ -89,7 +89,7 @@ Example: ::
const int uart_buffer_size = (1024 * 2);
QueueHandle_t uart_queue;
// Install UART driver using an event queue here
ESP_ERROR_CHECK(uart_driver_install(uart_num, uart_buffer_size, \
ESP_ERROR_CHECK(uart_driver_install(UART_NUM_2, uart_buffer_size, \
uart_buffer_size, 10, &uart_queue, 0));
If all above steps have been complete, we are ready to connect the other UART device and check the communication.
@@ -111,7 +111,7 @@ The basic API function to write the data to Tx FIFO buffer is :cpp:func:`uart_tx
There is a 'companion' function :cpp:func:`uart_wait_tx_done` that waits until all the data are transmitted out and the Tx FIFO is empty. ::
// Wait for packet to be sent
const int uart_num = UART_NUM_1;
const int uart_num = UART_NUM_2;
ESP_ERROR_CHECK(uart_wait_tx_done(uart_num, 100)); // wait timeout is 100 RTOS ticks (TickType_t)
An easier to work with function is :cpp:func:`uart_write_bytes`. It sets up an intermediate ring buffer and exits after copying the data to this buffer. When there is an empty space in the FIFO, the data are moved from the ring buffer to the FIFO in the background by an ISR. The code below demonstrates using of this function. ::
@@ -132,7 +132,7 @@ Receiving
To retrieve the data received by UART and saved in Rx FIFO, use function :cpp:func:`uart_read_bytes`. You can check in advance what is the number of bytes available in Rx FIFO by calling :cpp:func:`uart_get_buffered_data_len`. Below is the example of using this function::
// Read data from UART.
const int uart_num = UART_NUM_1;
const int uart_num = UART_NUM_2;
uint8_t data[128];
int length = 0;
ESP_ERROR_CHECK(uart_get_buffered_data_len(uart_num, (size_t*)&length));
@@ -188,7 +188,7 @@ If communication is established with :cpp:func:`uart_driver_install` for some sp
Overview of RS485 specific communication options
-------------------------------------------------
Note: Here and below the notation UART_REGISTER.UART_OPTION_BIT will be used to describe register options of UART. See the ESP32 Technical Reference Manual for more information.
.. note:: Here and below the notation UART_REGISTER.UART_OPTION_BIT will be used to describe register options of UART. See the ESP32 Technical Reference Manual for more information.
- UART_RS485_CONF_REG.UART_RS485_EN = 1, enable RS485 communication mode support.
- UART_RS485_CONF_REG.UART_RS485TX_RX_EN, transmitter's output signal loop back to the receiver's input signal when this bit is set.
@@ -202,8 +202,7 @@ The ESP32 UART hardware is not able to control automatically the RTS pin connect
Overview of RS485 interface connection options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Note: The example schematics below are prepared for just demonstration of basic aspects of RS485 interface connection for ESP32 and may not contain all required elements.
.. note:: The example schematics below are prepared for just demonstration of basic aspects of RS485 interface connection for ESP32 and may not contain all required elements. The Analog Devices ADM483 & ADM2483 are examples of common RS485 transceivers and other similar transceivers can also be used.
The circuit A: Collision detection circuit
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