[TUHS] Re: Of /dev/tty8

[segaloco via TUHS <tuhs@tuhs.org>]

On Monday, March 18th, 2024 at 1:08 PM, Ron Natalie <ron@ronnatalie.com> wrote:

> The other problem with the DZ is it was one interrupt per character if I
> recall.
> Thte DH you could get multiple (output) characters per interrupt.
> Greatly decreased the load on the system.
> 
> I do remember the KL kernel prints were not interrupt driven so the
> system pretty much froze while the kernel printfs were being output.
> There was a comment on the code saying this was “Not for idle chit
> chat.”

Yep, synchronous code that writes a character at a time to the transmit register then spins on a status bit awaiting transmit complete, or something like that.  I adapted the V6 kernel printf to a RISC-V board I was working on the past year to have a trustworthy print mechanism, only caveat being the transmitter status register was a dirty filthy liar and wouldn't flip the bit on transmit, so just had to put a delay, which it turns out all of the BSDs currently also do for Ti 16550-family UARTs as well.

- Matt G.