a1f9cdb1ab
These use the raw console interface and poll. Unfortunately, the SiFive UART puts the FIFO empty bit inside the FIFO data register, which means that the act of checking whether a character is available also dequeues any character from the FIFO, requiring the user to press each key twice. However, since we configure the watermark to be 0 and, when the UART has been grabbed for the console, we have interrupts off, we can abuse the interrupt pending register to act as a substitute for the FIFO empty bit. This perhaps suggests that the console interface should move from having rxready and getc to having getc_nonblock and getc (or make getc take a bool), as all the places that call rxready do so to avoid blocking on getc when there is no character available. Reviewed by: kp, philip MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D31025
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