Very Computer

Has anyone developed something like this for Linux/UNIX before?

In a related question, Does anyone have sample code of a Linux kernal module
writing to the
8254 timer chip on a typical PC?

Thanks and best regards.

Sang

SLee000 schrieb:

Quote:> I am developing a 'virtual/software' UART (Universal Asynchronous Receiver
> Transmitter).
> That is, using software to simulate the RS232 Serial port (COM0, COM1, COM2
> etc.).
> Instead of writing a byte to a hardware register and letting the hardware UART
> ( like an 8250 or
> 16550) shift the bits out, I will be doing the shifting in software,
> writing/reading only to
> a generic GPIO pin (as in an Intel Northbridge chipset) or to one pin of the
> parallel port.

You need a timer that issues interrupts at a rate of _least_ 4 times the baudrate
for receiving. You need to sample the input line at this clock. You need to do the
sampling directly in the ISR otherwise you will be delayed too long by the OS. But
even here I suppose you will see some glitches when Linux masks the interrupt at
unwanted times (even true with quite low baudrates). You can use RT/LINUX  or a
similar add-on to overcome this, but I think it's much to complex regarding the
hardware saving you want. It would be _much better_ adding a hardware UART to the
system somehow.