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Connecting the HRESP signals of an AHB master and an AHB-Lite slave?

Applies to: PL301 AMBA 3 HP Matrix

Scenario

We have configured one of the slave interfaces of the PL301 to use the AHB_LITE_MASTER protocol.  We observe that the HRESP signal is only one bit wide, while according to the AHB protocol, it has to be 2 bits.

Is there any configuration we are missing which is causing this port mismatch?

Answer

AHB-Lite (AMBA 3.0) does not support the SPLIT and RETRY slave responses that are supported in full AHB (from AMBA 2.0).

Looking at the HRESP signals in full AHB:

HRESP[1:0]
00 - OKAY
01 - ERROR
10 - RETRY
11 - SPLIT

Because RETRY and SPLIT are not supported, the only possible responses are OKAY and ERROR (which can be determined using only bit 0 of HRESP).

Therefore, if you have an HRESP signal elsewhere in your system that is 2 bits wide, you can connect only bit 0 to your AHB-Lite master.

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