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5.1 Intel 915PM North Bridge(1)
Host Interface Signals
Signal Name Type Description
HADS# I/O
AGTL+
Host Address Strobe:
The system bus owner asserts HADS# to indicate the first of two
cycles of a request phase. The GMCH can also assert this signal for
snoop cycles and interrupt messages.
HBNR# I/O
AGTL+
Host Block Next Request:
Used to block the current request bus owner from issuing a new
request. This signal is used to dynamically control the CPU bus
pipeline depth.
HBPRI# O
AGTL+
Host Bus Priority Request:
The GMCH is the only Priority Agent on the system bus. It asserts
this signal to obtain the ownership of the address bus. This signal has
priority over symmetric bus requests and will cause the current
symmetric owner to stop issuing new transactions unless the
HLOCK# signal was asserted.
HBREQ0# I/O
AGTL+
Host Bus Request 0#:
The GMCH pulls the processor bus HBREQ0# signal low during
HCPURST#. The signal is sampled by the processor on the
active-to-inactive transition of HCPURST#.
HBREQ0# should be tri-stated after the hold time requirement has
been satisfied.
HCPURST# O
AGTL+
Host CPU Reset:
The CPURST# pin is an output from the GMCH. The GMCH asserts
HCPURST# while RSTIN# is asserted and for approximately 1 ms
after RSTIN# is deasserted. HCPURST# allows the processor to
begin execution in a known state.
HDBSY# I/O
AGTL+
Host Data Bus Busy:
Used by the data bus owner to hold the data bus for transfers
requiring more than one cycle.
HDEFER# O
AGTL+
Host Defer:
Signals that the GMCH will terminate the transaction currently being
snooped with either a deferred response or with a retry response.
HDINV[3:0]# I/O
AGTL+
Host Dynamic Bus Inversion:
Driven along with the HFD[63:0]# signals. Indicates if the associated
signals are inverted or not. HDINVF[3:0]# are asserted such that the
number of data bits driven electrically low (low voltage) within the
corresponding 16-bit group never exceeds 8.
HDINV# Data Bits
HDINV[3]# HD[63:48]#
HDINV[2]# HD[47:32]#
HDINV[1]# HD[31:16]#
HDINV[0]# HD[15:0]#
Host Interface Signals (Continued)
Signal Name Type Description
HDRDY# I/O
AGTL+
Host Data Ready:
Asserted for each cycle that data is transferred.
HA[31:3]# I/O
AGTL+
2X
Host Address Bus:
HA[31:3]# connects to the CPU address bus. During processor cycles
the HA[31:3]# are inputs. The GMCH drives HA[31:3]# during
snoop cycles on behalf of DMI.
HA[31:3]# are transferred at 2x rate.
Note that the address is inverted on the CPU bus.
HADSTB[1:0]# I/O
AGTL+
2X
Host Address Strobe:
HA[31:3]# connects to the CPU address bus. During CPU cycles, the
source synchronous strobes are used to transfer HA[31:3]# and
HREQ[4:0]# at the 2x transfer rate.
Strobe Address Bits
HADSTB[0]# HA[16:3]#, HREQ[4:0]#
HADSTB[1]# HA[31:17]#
HD[63:0]# I/O
AGTL+
4X
Host Data:
These signals are connected to the CPU data bus. HD[63:0]# are
transferred at 4x rate.
Note that the data signals are inverted on the CPU bus depending on
the HDINV[3:0]# signals.
HDSTBP[3:0]#
HDSTBN[3:0]#
I/O
AGTL+
4X
Host Differential Host Data Strobes:
The differential source synchronous strobes are used to transfer
HD[63:0]# and HDINV[3:0]# at the 4x transfer rate.
Strobe Data Bits
HDSTBP[3]#, HDSTBN[3]# HD[63:48]#, HDINV[3]#
HDSTBP[2]#, HDSTBN[2]# HD[47:32]#, HDINV[2]#
HDSTBP[1]#, HDSTBN[1]# HD[31:16]#, HDINV[1]#
HDSTBP[0]#, HDSTBN[0]# HD[15:00]#, HDINV[0]#
HHIT# I/O
AGTL+
Host Hit:
Indicates that a caching agent holds an unmodified version of the
requested line.
Also, driven in conjunction with HITM# by the target to extend the
snoop window.
HHITM# I/O
AGTL+
Host Hit Modified:
Indicates that a caching agent holds a modified version of the
requested line and that this agent assumes responsibility for providing
the line.
Also, driven in conjunction with HIT# to extend the snoop window.
5. Pin Descriptions of Major Components
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