User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 8: PCI Bus and HyperTransport Fabric Page
239
Table 128: PCI Command Register - Offset 4 Bits [15:0]
Bits
Name
Default
Description
0
IoSpaceEn
R/O 1’b0
I/O Space Enable. This bit is always zero. The bridge never accepts I/O space
accesses from the PCI bus.
1
MemSpaceEn
R/W 1’b1
RevId>=3
R/W 1’b0
Memory Space Enable. This bit must be set to allow the bridge to accept memory
space accesses from the PCI bus and forward them to either ZBbus or the
HyperTransport bridge.
In interface revisions 1 and 2 this bit defaults to 1 to enable these accesses after
reset, in interface revision 3 and greater this bit defaults to 0 to match the PCI
specification.
2
MasterEn
R/W 1’b0
Bus Master Enable. This bit must be set to allow the bridge to act as a master on
the PCI bus. This bit should be set before any PCI accesses are made. Any
accesses to the PCI space that are received while this bit is clear will result in
UNDEFINED behavior in the interface.
3
SpecCycEn
R/O 1’b0
The bridge does not accept Special Cycles, so this bit is always zero.
4
MemWrInvEn
R/W 1’b0
This bit should be set to allow the bridge to generate Memory Write and Invalidate
commands. The bridge will only use Write Invalidate if the start address is
cacheline aligned and the transfer is at least one cache line long (using the cache
line size set in the ClineSz register).
If the latency timer expires while a Write Invalidate command is in progress the
access will only be terminated at the next cache line boundary.
5
VgaPalSnpEn
R/O 1’b0
This bit is always zero. The bridge does not snoop VGA palette accesses.
6
ParErrResp
R/W 1’b0
This bit controls the response to PCI parity errors. If it is set then the MstrDParErr
bit is set in the status register and the PCI error interrupt is raised when a parity
error is detected. If it is clear then no interrupt is raised. In both cases the DetParErr
bit is set in the status register.
A parity error resulting from a read will return data to the ZBbus with a bus error if
this bit is set, and returned as valid data if this bit is clear.
7
StepCtrl
R/O 1’b0
This bit is always clear. The bridge does not do address/data stepping.
8
SerrEn
R/W 1’b0
SERR enable. If this bit is set, the bridge will drive the SERR_L pin if it detects a
fatal error. If clear the bridge will never drive SERR_L.
9
FastB2BEn
R/O 1’b0
This bit is always clear. The bridge will never do fast back-to-back cycles to different
devices.
15:10
reserved
R/O 6’b0
Reserved
Table 129: PCI Status Register - Offset 4 Bits [31:16]
Bits
Name
Default
Description
3:0
reserved
R/O 4’b0
Reserved
4
CapList
R/O 1’b0
Always clear. There is no capabilities list.
5
66MHzCap
R/O 1’b1
This bit is set. The PCI is 66 MHz capable.
6
reserved
R/O 1’b0
Reserved
7
FastB2BCap
R/O 1’b1
This bit indicates that the bridge can accept fast back-to-back transactions when
the transactions are to different agents.
8
MstrDParErr
R/C 1’b0
This bit is set if the bridge was a bus master and detected a parity error on read
data, or was signalled that a parity error happened on write data. The ParErrEn bit
in the command register must be set to allow this bit to be set. If this bit is set the
PCI error interrupt is asserted. It is cleared by software writing a 1.
10:9
DevselTiming
R/O 2’b01
The bridge generates medium DEVSEL timing.