Re: Serial custom speed deprecated?

[Ian Stirling <ian.stirling@mauve.plus.com>]

linux@horizon.com wrote:
>> Or we could just add a standardised extra set of speed ioctls, but then
>> we need to decide what occurs if I set the speed and then issue a
>> termios call - does it override or not.
> 
<snip>
> Alternatively, you could observe that asynchronous communications only
> requires agreement withing 5% between sender and receiver, so specifying
> a baud rate to much better than 1% is not too important.

To nitpick.
For a 10 bit long word, if the receiver syncs to within 1/8th of  the 
middle of a bit-time at the start, you've got 2/8th of a bit-time of 
disagreement possible, before you are likely to get errors, especially 
on limited slew-rate signals. (more modern chips will likely sample faster)
Or 3/80, or 2.5%. If the other side has made a similar calculation, then 
you should only really rely on 1%.
5% is the best possible case - that will in most circumstances cause errors.