Re: serial ports
Baard Johannessen (bajohann@utopia.ppp.sn.no)
Tue, 6 Aug 1996 08:01:34 +0100
>> This is not a Linux limitation. It is due to the PC architecture. Some
>> special "inteligent" cards can achieve this by mean of a special driver.
>> Read the Serial-HOWTO, which stands
>>
>> " The number of serial ports you can use is limited by the number of
>> interrupts (IRQ) and port I/O addresses we have to use. This is not a
>> Linux limitation, but a limitation of the PC bus. Each serial devices
>> must be assigned it's own interrupt and address. A serial device can
>> be a serial port, an internal modem, or a multiport serial board.
>
>But this is not true. There must be another reason why Linux' serial
>driver doesn't allow multiple ports to use the same IRQ. The serial driver
>could very well ask the serial port if it was the one to generate the
>interrupt. Don't tell me it's impossible, I have done it myself. Just
>check base+2 for a zero in bit 0.
>Though, I wouldn't recommend doing so, since it makes the code weird.
Seems this could easily become a big discusion so I desided to add send
along a refferance to the ultimete PC serialport oracle!
Check out:
ftp.phil.uni-sb.de/pub/chris/The_Serial_Port
Or for the Netscape generation:
http://www.colargol.idb.hist.no/~bardj/serial/
It describes the ins and outs of PC serial ports, and also how to hack the
hardware to allow to ports to share an IRQ.
'nuff sayd :)
bardj