4−9
4.9 Bus Options Register
The bus options register externally maps to the second quadlet of the Bus_Info_Block. See Table 4−7 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 Bus options
Type R/W R/W R/W R/W R/W R R R R/W R/W R/W R/W R/W R/W R/W R/W
Default X X X X 0 0 0 0 X X X X X X X X
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Name Bus options
Type R/W R/W R/W R/W R R R R R/W R/W R R R R R R
Default 1 0 1 0 0 0 0 0 X X 0 0 0 0 1 0
Register: Bus options
Type: Read/Write, Read-only
Offset: 20h
Default: X0XX A0X2h
Table 4−7. Bus Options Register Description
BIT FIELD NAME TYPE DESCRIPTION
31 irmc R/W Isochronous resource-manager capable. IEEE 1394 bus-management field. Must be valid when bit 17
(linkEnable) in the host controller control register at OHCI offset 50h/54h (see Section 4.16, Host
Controller Control Register) is set to 1.
30 cmc R/W Cycle master capable. IEEE 1394 bus-management field. Must be valid when bit 17 (linkEnable) in the
host controller control register at OHCI offset 50h/54h (see Section 4.16, Host Controller Control
Register) is set to 1.
29 isc R/W Isochronous support capable. IEEE 1394 bus-management field. Must be valid when bit 17
(linkEnable) in the host controller control register at OHCI offset 50h/54h (see Section 4.16, Host
Controller Control Register) is set to 1.
28 bmc R/W Bus manager capable. IEEE 1394 bus-management field. Must be valid when bit 17 (linkEnable) in
the host controller control register at OHCI offset 50h/54h (see Section 4.16, Host Controller Control
Register) is set to 1.
27 pmc R/W Power-management capable. IEEE 1394 bus-management field. When bit 27 is set to 1, this indicates
that the node is power-management capable. Must be valid when bit 17 (linkEnable) in the host
controller control register at OHCI offset 50h/54h (see Section 4.16, Host Controller Control Register)
is set to 1.
26−24 RSVD R Reserved. Bits 26−24 return 0s when read.
23−16 cyc_clk_acc R/W Cycle master clock accuracy, in parts per million. IEEE 1394 bus-management field. Must be valid
when bit 17 (linkEnable) in the host controller control register at OHCI offset 50h/54h (see Section 4.16,
Host Controller Control Register) is set to 1.
15−12 max_rec R/W Maximum request. IEEE 1394 bus-management field. Hardware initializes this field to indicate the
maximum number of bytes in a block request packet that is supported by the implementation. This
value, max_rec_bytes, must be 512 or greater, and is calculated by 2^(max_rec + 1). Software may
change this field; however, this field must be valid at any time bit 17 (linkEnable) in the host controller
control register at OHCI offset 50h/54h (see Section 4.16, Host Controller Control Register) is set to
1. A received block write request packet with a length greater than max_rec_bytes may generate an
ack_type_error. This field is not affected by a software reset, and defaults to a value indicating
2048 bytes on a system (hardware) reset.
11−8 RSVD R Reserved. Bits 11−8 return 0s when read.
7−6 g R/W Generation counter. This field is incremented if any portion of the configuration ROM has been
incremented since the prior bus reset.
5−3 RSVD R Reserved. Bits 5−3 return 0s when read.
2−0 Lnk_spd R Link speed. This field returns 010, indicating that the link speeds of 100M bits/s, 200M bits/s, and
400M bits/s are supported.
