> Perhaps in theory but not in practice, you pass the address of a random
> value. Either the BIOS sets an error return code and does not modify the
> result, or it does not check and it writes all ones to the return value.
> However, in this case the BIOS modifies the return value, and it should be
> set 0xffffffff if the device is not present. The fact that only 1 or 2
> bits are wrong more likely indicates a hardware problem than anything else.
I expect the 0xffffffff to be a "read of an non-driven bus". This usually
turns out to lead to the value <all ones> however bit-errors are allowed:
nobody drove the bus.
On the other hand, you're saying there is a well-defined error
mechanism to detect non-present devices..... Maybe some chipsets don't
consider it important to implement that for configuration space?
Roger.
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