Correct IDSEL generation/identification.. ??

[Abraham Thomas <abraham_ktm@yahoo.com>]

Hello experts,

i have a doubt relating to IDSEL implementation...
if i understand right this is what the spec means:

the host-pci bridge decodes the "device number" in the
32 bit address (config. access to address port) it
gets from the CPU and uses one of the AD11-AD31 lines
(or more practically AD16-AD31 AD lines) for
generating IDSEL during address phase of conf/
transaction instead of using a separate IDSEL signal.
this IDSEL acts as a chip select for any one of
various devices in the bus. in modern PCs, the IDSEL
of the 1st device on the bus (which i believe means
the 1st slot?? -- clarify if incorrect) is connected
(/resistively coupled???) to AD16, 2nd to AD17 and so
on...

my doubt is: if we need to tell our target device to
use a particular AD line as chip select for it, how do
we know which AD line to tell it bcos this may change
if we change the slot in which we put our pci card?
won't our device work if placed on any other slot (ie,
if it takes any other device number??) bcos the the
logic for decoding the IDSEL is "burn"t inside the
target device... say, we could tell our card to OK a
config access if AD16 line is asserted. what if this
card is put in the next slot? in this case it won't
work.. it will work only if AD17 is asserted since
this is the way that the H/PCI bridge generates IDSEL.

what is the way around this? what's wrong in my
understanding? if there is no fixed logic to
understand which AD line is meant for our device, how
does the right IDSEL reach the right device?

kindly clarify.. 

thanks in advance
Happy Holidays!!

regards,
Abraham Thomas

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com