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Figure 9-2 Four-chip Loongson No. 3 interconnection structure
Loongson 3 interconnection routing
Loongson No. 3 interconnection routing adopts simple XY routing method. That is, when routing, X then Y, taking four chips as an example, ID
The numbers are 00, 01, 10, and 11, respectively. If a request is made from 11 to 00, it is a route from 11 to 00, first go to X
Direction, from 11 to 10, then Y direction, from 10 to 00. When the response to the request returns 11 from 00, the route
First go in the X direction, from 00 to 01, then go in the Y direction, from 01 to 11. As you can see, these are two different routes
line. Due to the characteristics of this algorithm, we will adopt different methods when constructing the interconnection of two chips.
Two piece Loongson No. 3 interconnection structure
Due to the nature of the fixed routing algorithm, we have two different methods when constructing the interconnection of two chips. The first is to adopt 8
Bit HT bus interconnection. In this interconnection method, only 8-bit HT interconnection can be used between the two processors. Two chip numbers
Don't be 00 and 01. From the routing algorithm, we can know that when two chips access each other, they are interconnected with
8-bit HT bus. As follows:
Figure 9-3 Two-chip Loongson No. 3 8-bit interconnection structure
However, our widest HT bus can use 16-bit mode, so the connection method to maximize bandwidth should be 16
CPU0
HT0_
HI
HT0_
LO
HT
1
CPU1
HT0_
HI
HT0_
LO
8-bit HT bus
IO
16-bit HT bus
CPU0
HT0_
HI
HT0_
LO
HT
1
CPU1
HT0_
HI
HT0_
LO
CPU3
HT0_
HI
HT0_
LO
CPU2
HT0_
HI
HT0_
LO
8-bit HT bus
8 bit
H
T total
line
8-bit HT bus
8 bit
H
T total
line
IO
16-bit HT bus
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Bit interconnect structure. In Godson III, as long as the HT0 controller is set to 16-bit mode, all are sent to the HT0 controller
Will be sent to HT0_LO instead of HT0_HI or HT0_LO according to the routing table.
In this way, we can use the 16-bit bus when interconnecting. Therefore, we only need to convert the 16-bit modulo of CPU0 and CPU1
The 16-bit HT bus interconnection can be used if the configuration is correctly configured and the high and low busses are correctly connected. And this interconnection structure al
The 8-bit HT bus protocol can be used for mutual access. The resulting interconnection structure is as follows: