Datasheet

1394 OHCI—PCI Configuration Space
120
March 5 2007 − June 2011SCPS154C
7.15 MIN_GNT and MAX_LAT Register
The MIN_GNT and MAX_LAT 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,
Latency Timer and Class Cache Line Size Register). If a serial EEPROM is detected, then the contents of this
register are loaded through the serial EEPROM interface. 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 7−11 for a complete
description of the register contents.
PCI register offset: 3Eh
Register type: Read/Update
Default value: 0402h
BIT NUMBER 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RESET STATE 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0
Table 7−11. MIN_GNT and MAX_LAT 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 OHCI controller. The default for this register indicates that the OHCI 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 RU Minimum grant. The contents of this field may be used by host BIOS to assign a latency timer register value
to the OHCI controller. The default for this register indicates that the OHCI 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 OHCI
controller latency timer and class cache line size register at offset 0Ch in the PCI configuration space (see
Section 7.6, Latency Timer and Class Cache Line Size Register). Bits 3−0 of this field may also be loaded
through the serial EEPROM.
†
These bits are reset by a PCI Express reset (PERST), a GRST, or the internally-generated power-on reset.
7.16 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 7−12 for a complete description of the register contents.
PCI register offset: 40h
Register type: Read/Write, Read-only
Default value: 0000 0000h
BIT NUMBER 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
RESET STATE 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
BIT NUMBER 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RESET STATE 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Table 7−12. OHCI Control Register Description
BIT FIELD NAME TYPE DESCRIPTION
31−1 RSVD R Reserved. Bits 31−1 return 000 0000 0000 0000 0000 0000 0000 0000b when read.
0 GLOBAL_SWAP RW When bit 0 is set to 1b, all quadlets read from and written to the PCI interface are byte-swapped (big
endian). The default value for this bit is 0b which is little endian mode.
Not Recommended for New Designs