>Since all other mice seem to be accessible through devfs I assumed
>this was also the case for serials.
>
>Damn , I was hoping this was going be followed in kernel space to
>guarantee not missing any pulses. Well there's other ways around that
>problem.
You already have a buffering kernel driver for the serial port.
A serial mouse is usually sending data at 1200 bps. Assuming a clean
signal from the mouse, you would have to work pretty hard to find a way
to miss mouse events.
The major areas I would watch out for are:
1. Some mouse devices have real rs232 drivers, but most of them were
designed to be sure the signal is just good enough to make it a whole 1
or 2 meters from the mouse to the computer. Some of them do not bother
to do the full +12/-12 volt swing of rs232. Check it out carefully if
using long wires from the mouse to your computer.
2. If the meter can turn faster than the mouse can send the motion events,
you have a problem. I would also check that the mouse really does send
a motion event every time you think it should. You might not notice
if a mouse fails to report a motion event now and then, so I wouldn't
have any high expectations that the guy who did the firmware paid close
attention to that aspect of the firmware. (On the other hand, a mouse
that loses button events is quite visibly broken.)
3. If you have a single process that tries to do a lot of other
things in addition to reading the data, you could have problems.
As a really extreme example, if you read a mouse event then print "Saw
mouse event. Continue?" and wait for the user to say "yes", you would
have a problem. :) Of course, you aren't going to do that, but if your
program does a lot of computation or i/o, it might prevent your process
from keeping up with the data stream. You have plenty of time to mess
around, though. 1200 baud is only 120 bytes per second, and it takes
several bytes to report a mouse event.
Fortunately, the kernel driver isn't going to make a difference to any
of these problems, so you do not need to worry about it. Regular
serial port programming is sufficient.
Mark S.
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