AHB Multilayer
Connect @ https://www.linkedin.com/in/avimit/ Aviral Mittal
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Now what is AHB Multilayer?
Consider an AHB arbiter, which connects M masters and S slaves.
This arbiter or AHB Bus arbitrates between M masters and grants the bus to one of them, say Master 2 or M2
Now M2 is interacting with some slave say S3.
While M2 is interacting with S3, all other masters in the system cannot do anything will M2 is busy.
Here we lose the opportunity, as while M2 is interacting with S3,
there is no reason why say M4 cannot interact with S1 simultaneously.
But with a single layered bus, this is not possible.
A Multilayered bus or arbiter enables just that,
so that any master can interact with any slave as long as the master/slave pair is unique.
For example while M2 is interacting with S3, M4 can interact with S2, M1 can interact with S1 simultaneously.
How is this possible?
This is possible when the arbitration takes place at the slave port. Each Slave will have say M interfaces,
So that M masters can connect to it.
There is now a path to each master in the system to each slave, so that simultaneous accesses can take place
if the Master/Salve pair is unique.

This multi-layer system will be essentially AHB-Lite. No Bus Requests no Bus Grants,
as conceptually there are multiple parallel buses, actually there are as many buses in the system
as there are number of slaves.

Where can I get a Multi-layered AHB bus RTL?
ARM:
Synopsys:

While ARM is a very efficient solution, very small design, Synopsys's design isn't small.
The reason is simple: Synopsys offers an IP which can do a Multi-master to Single Slave bus. DW_ahb_icm
This means if you have S slaves in your system, you will need S instances of this IP to build a MxS system.
The Synopsys Solution looks like this:





You will note that in the above architecture, not every master is connected to every slave.
Though you can connect every master to every slave, but in a realistic system, usually this is not the case
So the above diagram is more representative of a realistic scenario.
BTW the above is a 5x4 System. i.e. 5 Masters and 4 Slaves.


ARM has a native MxS solution, where M<=16, and S<=16. The design is very area efficient.


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