ARM Technical Support Knowledge Articles

Does the PL301 support locked transactions from AHB masters?

Applies to: PL301 AMBA 3 HP Matrix

Scenario

Does the PL301 support locked transactions from AHB masters?

Answer

The PL301 can be configured to have two styles of AHB-to-AXI bridge that support locked transactions:

1) ahb_lite_master/ahb_lite_slave bridge:

The 'ahb_lite_master/slave' bridge will only support AHB LOCKed sequences that are of the type produced by an ARM SWP instruction, so a single LOCKed READ access followed by a single LOCKed WRITE access. There is no support for any other LOCKed sequence of transfers.

2) ahb_lite_mem bridge:
The 'ahb_lite_mem' bridge will support any AHB LOCKed sequence, and this bridge will just convert this into an AXI LOCKed sequence. The final AXI transfer that ends the AXI LOCKed sequence will just be a dummy write access.

You have to be careful when selecting the 'ahb_lite_mem' option as it will convert incoming INCR bursts into bursts of length 4, and when there isn't a multiple of 4 transfers in the INCR burst, this results in read data being discarded (so cannot be used with read sensitive memory) and dummy write transfers with WSTRB=0 (so cannot be used with any SlaveInterface that can possibly be routed through to an AHB or APB MasterInterface (because they don't support WSTRB).

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