4.22 CardBus I/O Limit Registers 0, 1
These registers indicate the upper address of a PCI I/O address range. They are used by the PCI6x21/PCI6x11
controller to determine when to forward an I/O transaction to the CardBus bus, and likewise, when to forward a
CardBus cycle to PCI. The lower 16 bits of this register locate the top of the I/O window within a 64-Kbyte page, and
the upper 16 bits are a page register which locates this 64-Kbyte page in 32-bit PCI I/O address space. Bits 15−2
are read/write and allow the I/O limit address to be located anywhere in the 64-Kbyte page (indicated by bits 31−16
of the appropriate I/O base register) on doubleword boundaries.
Bits 31−16 are read-only and always return 0s when read. The page is set in the I/O base register. Bits 15−2 are
read/write and bits 1−0 are read-only, returning 00 or 01 when read, depending on the value of bit 12 (IO_LIMIT_SEL)
in the general control register (PCI offset 86h, see Section 4.31). Writes to read-only bits have no effect.
These I/O windows are enabled when either the I/O base register or the I/O limit register is nonzero. By default, the
I/O windows are not enabled to pass the first doubleword of I/O to CardBus.
Either the I/O base register or the I/O limit register must be nonzero to enable any I/O transactions.
Bit
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
Name
Type
Default
I/O limit registers 0, 1
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Name
Type
Default
I/O limit registers 0, 1
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
RW
0
R
0
R
X
Register:
Offset:
Type:
I/O limit registers 0, 1
30h, 38h
Read-only, Read/Write
0000 000Xh
Default:
4.23 Interrupt Line Register
The interrupt line register is a read/write register used by the host software. As part of the interrupt routing procedure,
the host software writes this register with the value of the system IRQ assigned to the function.
Bit
7
6
5
4
3
2
1
0
Name
Type
Default
Interrupt line
RW
1
RW
1
RW
1
RW
1
RW
1
RW
1
RW
1
RW
1
Register:
Offset:
Type:
Interrupt line
3Ch
Read/Write
FFh
Default:
4−13
TI [ TEXAS INSTRUMENTS ]
