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SubjectInterrupt sharing.
DateWed, 12 Feb 1997 12:47:35 +0000
FromDavid Woodhouse <>
I have two network cards in my Linux box - a Realtek 8029 and a 3Com 3c509. 
The former has support in the kernel, and the latter is available as a module. 
If I tell them both to use the same interrupt, the first card will work fine 
until I ifconfig the second, at which point it takes over the IRQ and never 
gives it back. Is this the correct behaviour? Should they be able to share the 
interrupts? If not, should not the 3c509 driver at least restore the IRQ 
handler to it's original state when it finishes, so the other card can 
continue working?

Also, the 3c509 driver attempts to release the IRQ twice - once when 
ifconfig'ed down and again when the module is removed. Is this a hangover from 
the time when it used to hog the IRQ all the time it was installed?

With regard to sharing of interrupts, will the kernel handle more than one 
serial port on the same IRQ simultaneously (i.e. COM1/3, COM2/4) ?
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      David Woodhouse,            WWW: http://dwmw2.robinson.cam.ac.uk
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