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SubjectRe: serial ports
On Mon, 5 Aug 1996, Magnus Hiie wrote:

> Why is it impossible for multiple (standard) serial ports (ttyS?) to
> use the same IRQs?
> Is it some hardware limitation or what? When an interrupt occurs,
> serial driver could look up which port it was meant for, couldn't it?

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.

Multiport serial boards are specially designed to have multiple serial
ports that share the same IRQ for all serial ports on the board.
Linux gets data from them by using a different I/O address for each
port on the card.


Carlos Augusto Moreira dos Santos
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