On  8 Feb 98 at 14:43, Brad Britton wrote:

>   When my pc is downloading a page from the internet, I find that
> when I try to do something in the background that involves the
> mouse (click on a file to request it, try to paste info into a
> file,ect.) I most often have to click several times before the
> clicks do anything.I only began noticing this over the past month or
> two, but it could be that it was always like this. (Pentium 75,
> 32Meg RAM).
>   I suspect that this might be happening because I have the modem
> set up as COM 2, which I think has a higher priority IRQ than COM
> 1. The mouse will work after several clicks, even while the page is
> being downloaded.
>
>   Is this because I happen to click the mouse when the serial port
> buffer is empty?

  More likely, it's because you happen to click the mouse when the
CPU has a few cycles to spare.  I see similar effects using the mouse
while copying a lot of files from one drive to another -- no serial
port interference there.

>   I guess having a PS2 mouse would solve this, since the IRQ is at a
> higher priority level, but I don't have a PS2 port.
>   If I'm right about this so far, I guess if I moved the modem to
> COM1 and the mouse to COM2 this might fix this annoyance.

  That might work. [I have my mouse on COM2 and modem on COM3, and I
haven't seen this problem during download.  Hmmm...]

>   Also, I don't understand why after I click the mouse, I can't just
> wait for the result, instead of having to keep on clicking the
> mouse.

  Although a click seems like it might be just a single bit, every
click or movement (!) of the mouse sends 3-5 characters to the port
on the PC.  So even with a 16550A, only about 3-5 mouse events can be
queued up before additional events will be lost -- and on anything
less, not even one.

>   If an interrupt isn't serviced right away, does it just disappear?
> Can someone please comment on any of this? I don't know how much, if
> any, of what I have written here is accurate.

  The interrupt may not go away, but the several characters that the
mouse driver needs to receive may have been overrun and lost, and it
may take a click or two to get back into sync.

David G


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