PCI7421 datasheet(171/298 Pages) TI

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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

Name

Minimum grant and maximum latency

Type

Default

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

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

µs; 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

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

µs 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

Name

OHCI control

Type

Default

Bit

Name

OHCI control

Type

Default

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

Reserved. Bits 31−1 return 0s when read.

GLOBAL_SWAP

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.

PCI7421 Datasheet(PDF) 171 Page - Texas Instruments

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