1. Add a ring buffer for UART TX.
If the buffer size is set to zero, driver will not use a buffer. But we need a task to send data from buffer to fifo. I tried directly copy data in ISR, but the code looked too long for ISR.
2. Modify the format in uart.h
1. Use esp_log API for LEDC and GPIO code.
2. Modify some API return value.
3. Add ledc_set_pin() for LEDC
4. Modify typo in uart.h
Questions: In uart driver ISR handler, I used xxxFromISR , like xSemaphoreGiveFromISR, do those FromISR functions need to be put in IRAM?
1. configure LEDC timer saparately
2. add peripher_crtl.c/.h
To enable the peripheral modules, we have to set/clear the control register in dport_reg.h.
These bits are disabled by default and they are all in a same register, so we need to add a lock on that.
3. add include esp_err.h in gpio.h
