16
Network-on-Chip
Figure 2.3
A 4 × 4 2D torus with single core connected to each router.
Number of routers required: (M × N)
Node degree: 5
For a larger network, this wraparound link will be long enough and will
cause excessive delay.
A folded torus solves the problem of excessive delay in the long wraparound
connections of torus by folding it (Dally and Seitz 1986). Figure 2.4 shows a
4 × 4 folded torus network. A folded torus network having M rows and N
columns has the following parameters:
Diameter: ⌊M/2⌋ + ⌊N/2⌋
Bisection width: 2 × min(M,N)
Number of routers required: (M × N)
Node degree: 5
To reduce the average hop count of a mesh structure, a concentrated mesh
(CMESH) topology (Balfour and Dally 2006) has been proposed where four
cores are connected to each router. Thus, the number of routers required