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9.8.4. Supported AHB protocol features

The AHB-Lite master port supports AHB in AMBA v2.0.

HPROT encodings

HPROT[3:0] is provided as an external port and is programmed from the Prot field in the CSW register with the following conditions:

  • HPROT[3:0] programming is supported.

  • Exclusive access is not supported, so HRESP[2] is not supported.

See AHB-AP Control/Status Word Register, CSW, 0x00 for values of the Prot field.

HRESP

HRESP[0] is the only RESPONSE signal required by the AHB-AP:

  • AHB-Lite devices do not support SPLIT and RETRY and so HRESP[1] is not required.

  • HRESP[2] is not supported in the AHB-AP.

AHB-AP transfer types and bursts

The AHB-AP cannot initiate a new AHB transfer every clock cycle (unpacked) because of the additional cycles required to serial scan in the new address or data value through a debug port. The AHB-AP supports two HTRANS transfer types, IDLE and NONSEQ.

  • When a transfer is in progress, it is of type NONSEQ.

  • When no transfer is in progress and the AHB-AP is still granted the bus then the transfer is of type IDLE.

The only unpacked HBURST encoding supported is SINGLE. Packed 8-bit transfers or 16-bit transfers are treated as individual NONSEQ, SINGLE transfers at the AHB-Lite interface. This ensures that there are no issues with boundary wrapping, to avoid additional AHB-AP complexity.

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