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When you want to retrieve the actual base address of a BAR, be sure to mask (that is, clear) the lower bits. For Memory Space BARs, you calculate (BAR & 0xFFFFFFF0). For I/O Space BARs, you calculate (BAR & 0xFFFFFFF8). Do '''not''' shift the bits to the right or the values will be incorrect.
When you want to retrieve the actual base address of a BAR, be sure to mask the lower bits. For Memory Space BARs, you calculate (BAR & 0xFFFFFFF0). For I/O Space BARs, you calculate (BAR & 0xFFF8).


To determine the size of memory maps needed by a PCI device, you must read the BAR .
To determine the size of memory maps needed by a PCI device, you must read the BAR .
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