[uart] fix UART line-ending (#9)

This commit disables CRLF conversion in ESP_IDF vfs/uart module every
time we write radio frame through UART and enables the conversion for
CLI UART after finishing writing radio frame. This works because the
OpenThread stack is ran in a single task/thread, so there is no CLI
operations when we are reading or writing RADIO UART.

example/README.md

@@ -77,8 +77,6 @@ Connect to the ESP32 board from the Linux host:
 make monitor
 ```
 
-_Note: Dependending on your Linux distribution, the new line characters ('\r', '\n') may cause commands display issues. To have good look of the CLI, Connect the ESP32 board with advanced command `picocom -b 115200 /dev/ttyUSB0 --imap lfcrlf` (install `picocom` with `sudo apt-get install picocom`)._
-
 The CLI application is now in interactive mode and waiting for commands, start the OpenThread stack to verify your setup:
 
 ```shell

src/spinel_hdlc.cpp

@@ -210,7 +210,14 @@ otError HdlcInterface::Write(const uint8_t *aFrame, uint16_t aLength)
 
     while (aLength)
     {
-        ssize_t rval = write(mUartFd, aFrame, aLength);
+        ssize_t rval;
+
+        // Configure ESP-IDF UART to never convert "\n" to "\r\n" just before
+        // writing radio frames through UART. This is a workaround for issue:
+        // https://github.com/openthread/ot-esp32/issues/5.
+        esp_vfs_dev_uart_set_tx_line_endings(ESP_LINE_ENDINGS_LF);
+        rval = write(mUartFd, aFrame, aLength);
+        esp_vfs_dev_uart_set_tx_line_endings(ESP_LINE_ENDINGS_CRLF);
 
         if (rval > 0)
         {

src/uart.c

@@ -96,7 +96,7 @@ void platformCliUartInit()
     esp_vfs_dev_uart_use_driver(OT_CLI_UART_NUM);
 
     esp_vfs_dev_uart_set_rx_line_endings(ESP_LINE_ENDINGS_LF);
-    esp_vfs_dev_uart_set_tx_line_endings(ESP_LINE_ENDINGS_LF);
+    esp_vfs_dev_uart_set_tx_line_endings(ESP_LINE_ENDINGS_CRLF);
 
     sprintf(uartPath, "/dev/uart/%d", OT_CLI_UART_NUM);
     sCliUartFd = open(uartPath, O_RDWR | O_NONBLOCK);