Functional Description
3–3
Digital Semiconductor 21174 Core Logic Chip
Figure 3–2 shows the AlphaPC 164UX implementation of the 21174 core logic chip.
Figure 3–2 Main Memory Interface
3.2.1 21174 Chip Overview
The 21174 application-specific integrated circuit (ASIC) accepts addresses and com-
mands from the 21164 microprocessor and drives the main memory array with the
address, control, and clock signals. It also provides an interface to the 64-bit PCI I/O
bus.
The 21174 chip provides the following functions:
•
Serves as the interface between the 21164 microprocessor, main memory
(addressing and control), and the PCI bus. A three-entry CPU instruction queue
is implemented to capture commands should the memory or I/O port be busy.
•
Provides control to the Data Switch chips to isolate the L3 cache from the main
memory bus during private reads and writes.
21164
pc164ux.1-2
* addr_bus_req
adr_cmd_par
cack
cmd<3:0>
dack
fill
fill_error
fill_id
idle_bc
int4_valid<3:0>
sys_res<1:0>
tag_ctl_par
tag_dirty
victim_pending
21174
dram_addr<13:0>
*we
*cas
*ras
miscellaneous
pc164ux.8-10
Buffers
pc164ux.15-17
buf_addr<13:0>
*buf_we<5:0>
paddr<39:4>
*System Control
pdata<127:0>
pecc<15:0>
Data
Switches
(X5)
pc164ux.11
enabledataswitch<0:2>
pc164ux.12-14
DIMM 3
DIMM 2
DIMM 1
DIMM 0
mdata<128:0>
mecc<15:0>
64-Bit PCI
I/O Bus
*buf_cas<5:0>
*buf_ras<5:0>
buf_miscellaneous
DIMM 4
DIMM 5