AHB Fundas
Connect @ https://www.linkedin.com/in/avimit/ Aviral Mittal
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1. An AHB Slave should not pull 'HREADY' low, if it has 'HTRANS' = NSEQ, i.e HTRANS = 2.
This will be protocol violation.
By spec, "The address cannot be extended, therefore all slaves must sample the address during this time"
However, an 'Address Phase' could be extended as a side effect, if it coincides with Data Phase of previous
transaction.
HREADY indicates a transfer complete, it may then follow that a Slave may never pull down its HREADY
to low, while its HTRANS is 0. Because this will mean that Slave is trying to extend a NOP?

An AHB slave must respond OKAY in the next cycle with no wait state if the HTRANS is IDLE or BUSY, or if HSEL is not active.

AHB_info From the Spec
 IDLE or BUSY transfers to nonexistent locations should result in a zero wait state OKAY response.

If a slave provides an ERROR response then the master may choose to cancel the remaining transfers in the burst. However, this is not a strict requirement and it is also acceptable for the master to continue the remaining transfers in the burst.

A slave can only accept transfers that are as wide as its natural interface. If a master attempts a transfer that is wider than the slave can support then the slave can use the ERROR transfer response

2. Though the AHB spec itself puts no restriction on a combinatorial path from issuing Master back to Issuing
Master, but it should be avoided.


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KeyWords: AHB bufferable i.e. Posted Writes.