Serial issues

[solawc]

The stability and speed of serial communication has always been a major pain point hindering GRBL. At present, the serial port uses a polling serial port to send and receive. It receives through interrupts, enters the buffer, and finally gets a single character from the buffer, and composes a line of statements by itself. Therefore, the receiving speed can well hinder the execution efficiency of GRBL, so it is necessary to change the serial port transceiver of GRBL to use DMA to operate. This will save more performance for the MCU and get faster processing speed. One receive interrupt is always more stable than frequent receive interrupts, especially if you have an RTOS.