AHB Split


AHB Split Response
How does a AHB Split Response help?

Background:
In a AHB based Interconnect system, where the interconnect is essentially an AHB Bus, the bus is owned
by 1 master at a time, and it is held by the master at least till it completes the ongoing transfer.
Now what if a slave is presented by a read command, and the slave is incredibly slow. Say it takes
multiple clock cycles to produce the data it is requested to provide. Now starting from the point of time read
transaction is presented to slave, till it ready to produce response, the slave will pull hready low, and will
keep the bus engaged. Now the whole system is stalled, and no other master is able to do any operation.

The SPLIT response now comes into picture, and is able to change this scenario.
The AHB protocol allows the slave to issue a SPLIT response to a transaction, thereby relinquishing the bus
for the other masters in the system to be able to use the bus. As the slave issues a SPLIT response, it records
the master ID (HMASTER) of the transaction and memorises it.
When this slave is ready to respond to the SPLITted transaction, it informs the arbiter using HSPLIT signal.
HSPLIT has 1 bit for every master, and a '1' in a bit specifies which master this Slave is talking about.
The arbiter would then grant the bus to the SPLITted master on the earliest opportunity, and let it complete
the transaction.
This improves the overall system performance.


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