16 minimum grant and maximum latency register, 17 ohci control register – Texas Instruments Dual/Single Socket CardBus and UntraMedia Controller PCI7621 User Manual
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7−11
7.16 Minimum Grant and Maximum Latency Register
The minimum grant and maximum latency register communicates to the system the desired setting of bits 15−8 in
the latency timer and class cache line size register at offset 0Ch in the PCI configuration space (see Section 7.6).
If a serial EEPROM is detected, then the contents of this register are loaded through the serial EEPROM interface
after a GRST. If no serial EEPROM is detected, then this register returns a default value that corresponds to the
MAX_LAT = 4, MIN_GNT = 2. See Table 7−13 for a complete description of the register contents.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Name
Minimum grant and maximum latency
Type
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
RU
Default
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
Register:
Minimum grant and maximum latency
Offset:
3Eh
Type:
Read/Update
Default:
0402h
Table 7−13. Minimum Grant and Maximum Latency Register Description
BIT
FIELD NAME
TYPE
DESCRIPTION
15−8 ‡
MAX_LAT
RU
Maximum latency. The contents of this field may be used by host BIOS to assign an arbitration priority level
to the PCI7x21/PCI7x11 controller. The default for this register indicates that the PCI7x21/PCI7x11
controller may need to access the PCI bus as often as every 0.25
µ
s; thus, an extremely high priority level
is requested. Bits 11−8 of this field may also be loaded through the serial EEPROM.
7−0 ‡
MIN_GNT
RU
Minimum grant. The contents of this field may be used by host BIOS to assign a latency timer register value
to the PCI7x21/PCI7x11 controller. The default for this register indicates that the PCI7x21/PCI7x11
controller may need to sustain burst transfers for nearly 64
µ
s and thus request a large value be
programmed in bits 15−8 of the PCI7x21/PCI7x11 latency timer and class cache line size register at offset
0Ch in the PCI configuration space (see Section 7.6). Bits 3−0 of this field may also be loaded through the
serial EEPROM.
‡ These bits are cleared only by the assertion of GRST.
7.17 OHCI Control Register
The PCI OHCI control register is defined by the 1394 Open Host Controller Interface Specification and provides a
bit for big endian PCI support. See Table 7−14 for a complete description of the register contents.
Bit
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
Name
OHCI control
Type
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
Default
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Name
OHCI control
Type
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
RW
Default
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Register:
OHCI control
Offset:
40h
Type:
Read/Write, Read-only
Default:
0000 0000h
Table 7−14. OHCI Control Register Description
BIT
FIELD NAME
TYPE
DESCRIPTION
31−1
RSVD
R
Reserved. Bits 31−1 return 0s when read.
0
GLOBAL_SWAP
RW
When bit 0 is set to 1, all quadlets read from and written to the PCI interface are byte-swapped (big
endian). The default value for this bit is 0 which is little endian mode.