2.4 Protection control translation

For protection control, the AXI5 to AHB5 bridge maps the axcache and axprot AXI signals to the hprot and hnonseq AHB signals.

The following table shows how the AXI5 to AHB5 bridge converts the protection control from AXI5 to AHB5.

Table 2-5 Protection control mapping

AHB signals AHB bit number, function Value is derived from AXI signal:
hprot Bit[6], Shareable

axdomain. The hprot[6] signal is set to:

  • 0 if axdomain == 0b00 or 0b11. A Non-shareable or System transaction translates to a Non-shareable AHB transfer.
  • 1 if axdomain == 0b01 or 0b10. An Inner Shareable or Outer Shareable transaction translates to a Shareable AHB transfer.

ardomain and awdomain do not exist in the AXI protocol. The ACE protocol uses a concept that is called shareability domains and the axdomain signals indicate the shareability domain of a transaction. See the Arm® AMBA® AXI and ACE Protocol Specification for more information.

Bit[5], Allocate

arcache[2] for read transactions.

awcache[3] for write transactions.

Bit[4], Lookup

axcache[3:2] The hprot[4] signal is set to:

  • 0 if axcache[3:2] == 0b00.
  • 1 if axcache[3:2] != 0b00.
Bit[3], Modifiable axcache[1]
Bit[2], Bufferable axcache[0] The hprot[2] signal is set to:
  • axcache[0] for all transactions, except for a Normal Non-cacheable Bufferable transaction.
  • !axcache[0] for a Normal Non-cacheable Bufferable transaction (axcache[3:0] == 0b0011).
Bit[1], Privileged axprot[0]
Bit[0], Data/Opcode !axprot[2]
hnonsec Bit[0], Secure axprot[1]
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