Host Controller Data Manual

3–10
3.14 MIN_GNT and MAX_LAT Register
The MIN_GNT and MAX_LAT register is used to communicate to the system the desired setting of bits 15–8 of the
latency timer and class cache line size register (offset 0Ch, see Section 3.7). If a serial ROM is detected, then the
contents of this register are loaded through the serial ROM interface after a PCI reset. If no serial ROM is detected,
then this register returns a default value that corresponds to the MIN_GNT = 2, MAX_LAT = 4. See Table 3–11 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 MIN_GNT and MAX_LAT
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: MIN_GNT and MAX_LAT
Type: Read/Update
Offset: 3Eh
Default: 0402h
Table 3–11. MIN_GNT and MAX_LAT Register Description
BIT FIELD NAME TYPE DESCRIPTION
15–8 MAX_LAT RU
Maximum latency. The contents of this register may be used by host BIOS to assign an arbitration
priority-level to the TSB12LV26. The default for this register indicates that the TSB12LV26 may need to
access the PCI bus as often as every 0.25 µs; thus, an extremely high priority level is requested. The
contents of this field may also be loaded through the serial ROM.
7–0 MIN_GNT RU
Minimum grant. The contents of this register may be used by host BIOS to assign a latency timer and class
cache line size register (offset 0Ch, see Section 3.7) value to the TSB12LV26. The default for this register
indicates that the TSB12LV26 may need to sustain burst transfers for nearly 64 µs; thus, requesting a large
value be programmed in bits 15–8 of the TSB12LV26 latency timer and class cache line size register.
3.15 OHCI Control Register
The OHCI control register is defined by the 1394 Open Host Controller Interface Specification and provides a bit for
big endian PCI support. See Table 3–12 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 R/W
Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Register: OHCI control
Type: Read/Write
Offset: 40h
Default: 0000 0000h
Table 3–12. OHCI Control Register Description
BIT FIELD NAME TYPE DESCRIPTION
31–1 RSVD R Reserved. Bits 31–1 return 0s when read.
0 GLOBAL_SWAP R/W
When this bit is set, all quadlets read from and written to the PCI interface are byte swapped (big
endian). This bit is loaded from ROM and should be programmed to 0 for normal operation.