In message 200710010620.50106.vapier@gentoo.org you wrote:
i'm not claiming this is going to turn a 100mhz proc into 1000mhz proc or something, but in the tail end of writing to the UART, you would free up the CPU to continue ... and the processor tends to be a lot faster than the speed of a UART, so it could chew through a sizable chunk of code before the UART finishes shifting out a single byte ... and depending on the hardware, you could be talking about 1 byte, 5 bytes, or more
So you might end up saving 1 or 5 or a few more milliseconds.
maybe ... you'd have to mess up the processor pretty bad such that it breaks the peripherals ... the UART in a Blackfin acts independently of the core
So I vote for not removing this transmitter empty check.
i'd note that this is pretty inconsistent across different ports ...
I agree with Stefan. Please don't change this. The current implemen- tation (wait until trasmit has completed) is what I prefer.
so when do you return ? after making sure the byte has moved from the core to the peripheral hardware ? after making sure the byte has started to be shifted out from the peripheral onto the line ? after making sure the byte has been completed shifted onto the line ? the current Blackfin serial driver exhibits the last -- it waits until the whole byte has gone through the whole process, from core through the line
If that's how it was implemented, then leave it that way. It's OK.
Best regards,
Wolfgang Denk