RTEMS 4.6.1 On-Line Library

Timer Driver gen68340 UART FIFO Full Mode

BSP and Device Driver Development Guide

10.2: gen68340 UART FIFO Full Mode

The gen68340 BSP is an example of the use of the timer to support the UART input FIFO full mode (FIFO means First In First Out and roughly means buffer). This mode consists in the UART raising an interrupt when n characters have been received (n is the UART's FIFO length). It results in a lower interrupt processing time, but the problem is that a scanf primitive will block on a receipt of less than n characters. The solution is to set a timer that will check whether there are some characters waiting in the UART's input FIFO. The delay time has to be set carefully otherwise high rates will be broken:

if no character was received last time the interrupt subroutine was entered, set a long delay,
otherwise set the delay to the delay needed for n characters receipt.

BSP and Device Driver Development Guide