Two HBM controllers share an 8x8 switch. HBM controllers comprise two pseudo channels, each with two NSU ports. The 8x8 switch can route HNoC packets to either pseudo channel of either HBM controller. If a packet needs to reach an HBM controller outside of the pair, it goes to a different switch at the HNoC. There are no connections between 8x8 switches.
The following figure shows eight inputs to the switch. A solid arrow shows an 'even.' A dotted arrow shows an 'odd.'
The switch can route any even input to a solid arrow output and an odd input to a dotted arrow output. This allows any input to the switch to reach the HBM address space spanned across four pseudo channels. Two NSU ports to each pseudo channel ensures sufficient bandwidth to fully use the HBM throughput.