writing/finding pci bar0

i'm struggling to learn/understand pci direct access from user space.
i have a test system, system board parallel port is disabled, and
a pci parallel port card is installed. using lspci i can see
base_address_0 as 0xfc98. i've written some code to wiggle bits
on that card by writing to 0xfc98. using setpci i can change
BAR0 address to 0x378. however, the card only responds for a
few minutes. if i rewrite base_address_0 back to card a few
times, it will come back for awhile. what am i doing wrong
here? can you not manually change the base address in this
manner?
when i look a the output of lspci -bvx, the value stored at
offset 0x10 is one higher than the actual base address. why
is this?

.

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