[t13] Detecting two devices jumpered as device 0 / 1

[Thomas Jansen]

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Hi,

I was just wondering if it is possible to detect whether two devices are 
simultaneously jumpered as device 0 or 1.

In case of an ATA and ATAPI unit, issuing a command EC and getting the 
status 0x59 does the trick. But what if  two ATA/ATAPI units are used. I 
know the ID data checksum (if supported) will probably fail but that can be 
caused by other reasons as well.

I have been playing with the thought to count the asserted IRQs but when 
both devices fire their  interrupts almost simultaneously I assume I'll 
detect only one.

This lead two the following question ...

How does the service interrupt handle this? Assuming  device 1 asserts the 
interrupt line exactly at the same time device 0  asserts it. Does device 1 
sample the interrupt line to check whether it's already asserted? If so, 
what if two devices want to assert their service interrupts at exactly the 
same time? (somewhat like a network collision)

Thanks is advance,

Thomas