Datasheet

Processor Configuration Registers
102 Datasheet, Volume 2
2.6.24 BCTRL1—Bridge Control Register
This register provides extensions to the PCICMD register that are specific to PCI-to-PCI
bridges. BCTRL1 provides additional control for the secondary interface (that is, PCI
Express-G) as well as some bits that affect the overall behavior of the "virtual" Host-
PCI Express bridge embedded within the processor (such as, VGA compatible address
ranges mapping).
B/D/F/Type: 0/1/0–2/PCI
Address Offset: 3E–3Fh
Reset Value: 0000h
Access: RW, RO
Size: 16 bits
BIOS Optimal Default 0h
Bit Attr
Reset
Value
RST/
PWR
Description
15:12 RO 0h Reserved
11 RO 0b Uncore
Discard Timer SERR# Enable (DTSERRE)
Not Applicable or Implemented. Hardwired to 0.
10 RO 0b Uncore
Discard Timer Status (DTSTS)
Not Applicable or Implemented. Hardwired to 0.
9RO 0bUncore
Secondary Discard Timer (SDT)
Not Applicable or Implemented. Hardwired to 0
.
8RO 0bUncore
Primary Discard Timer (PDT)
Not Applicable or Implemented. Hardwired to 0.
7RO 0bUncore
Fast Back-to-Back Enable (FB2BEN)
Not Applicable or Implemented. Hardwired to 0.
6RW 0bUncore
Secondary Bus Reset (SRESET)
Setting this bit triggers a hot reset on the corresponding PCI
Express Port. This will force the TXTSSM to transition to the Hot
Reset state (using Recovery) from L0, L0s, or L1 states.
5RO 0bUncore
Master Abort Mode (MAMODE)
Does not apply to PCI Express. Hardwired to 0
.
4RW 0bUncore
VGA 16-bit Decode (VGA16D)
This bit enables the PCI-to-PCI bridge to provide 16-bit decoding of
VGA I/O address precluding the decoding of alias addresses every
1 KB. This bit only has meaning if bit 3 (VGA Enable) of this
register is also set to 1, enabling VGA I/O decoding and forwarding
by the bridge
.
0 = Execute 10-bit address decodes on VGA I/O accesses.
1 = Execute 16-bit address decodes on VGA I/O accesses.
3RW 0bUncore
VGA Enable (VGAEN)
This bit controls the routing of processor-initiated transactions
targeting VGA compatible I/O and memory address ranges. See
the VGAEN/MDAP table in Device 0, offset 97h[0].
2RW 0bUncore
ISA Enable (ISAEN)
Needed to exclude legacy resource decode to route ISA resources
to legacy decode path. Modifies the response by the root port to an
I/O access issued by the processor that target ISA I/O addresses.
This applies only to I/O addresses that are enabled by the IOBASE
and IOLIMIT registers.
0 = All addresses defined by the IOBASE and IOLIMIT for
processor I/O transactions will be mapped to PCI Express-G.
1 = The root port will not forward to PCI Express-G any I/O
transactions addressing the last 768 bytes in each 1KB block
even if the addresses are within the range defined by the
IOBASE and IOLIMIT registers.