A–28
System Address Space
PCI Configuration Space
Peripherals are selected during a PCI configuration cycle if the following three con-
ditions are met:
1.
Their IDSEL pin is asserted.
2.
The PCI bus command indicates a configuration read or write.
3.
Address bits <1:0> are 00.
Address bits <7:2> select a Dword (longword) register in the peripheral’s 256-byte
configuration address space. Transactions can use byte masks.
Peripherals that integrate multiple functional units (for example, SCSI and Ethernet)
can provide configuration space for each function. Address bits <10:8> can be
decoded by the peripheral to select one of eight functional units.
Signals ad<31:11> are available to generate the IDSEL bits (note that IDSEL bits
behind a PCI-to-PCI bridge are determined from the device field encoding of a type
1 access). The IDSEL pin of each device is connected to a unique PCI address bit
from ad<31:11>. The binary value of addr_h<20:16> is used to select which
ad<31:11> is asserted, as shown in Table A–9.
Table A–9 CPU Address to IDSEL Conversion
CPU Address <20:16>
ad<31:11> – IDSEL
00000
0000 0000 0000 0000 0000 1
00001
0000 0000 0000 0000 0001 0
00010
0000 0000 0000 0000 0010 0
00011
0000 0000 0000 0000 0100 0
.....
.... .... .... .... .... .
.....
.... .... .... .... .... .
10011
0100 0000 0000 0000 0000 0
10100
1000 0000 0000 0000 0000 0
10101
0000 0000 0000 0000 0000 0
.....
...(No device selected)
.....
—
11111
0000 0000 0000 0000 0000 0