ARM AMBA NIC-301 - Manual (Page 24)

Functional Description
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AHB master interfaces
The network can support the full AHB-Lite master protocol and you can configure the network
to provide an AHB-Lite mirrored slave protocol. Table 2-2 shows the mapping of AXI burst
types to AHB burst types.
Note
Transactions from AHB slave interfaces are output as INCR transactions of an undefined length.
If the AHB protocol conversion function receives an unaligned address, or a write data beat
without all the byte strobes set, the AMBA Network Interconnect detects it, and a programmable
enable bit permits the network to create a DECERR response.
Note
• If you set the
force_incr
programmable bit, see Table 3-3 on page 3-6, and a beat is
received that has no write data strobes set, that write data beat is replaced with an IDLE
beat.
• You can configure the inclusion of the programmable enable bit to create a reduced gate
count implementation.
See Chapter 3 Programmers Model. The network still transmits the unaligned address transfer
into the AHB domain, but it aligns the address by forcing the lower address bits of the
transaction’s size to zeros.
The network breaks any transactions that cross a 1KB boundary into two AHB INCR bursts.
You can configure a programmable option, named
force_incr
, see Table 3-3 on page 3-6, that
maps all transactions that are to be output to the AHB domain to be an undefined length INCR.
If the AXI burst is part of a locked sequence, the AHB-Lite translation keeps HMASTLOCK
asserted across the boundary to ensure that the burst atomicity is not compromised. For write
transactions, AHB responses are merged into a single AXI buffered response. The merged
response is an AXI SLAVE ERROR if any of the AHB-Lite data beats have an AHB ERROR.
Table 2-2 AXI burst type to AHB burst type mapping
AxBURST AxLEN HBURST Notes
FIXED - SINGLE This is a series of singles and the number
depends on the AxLEN setting
INCR 1 SINGLE -
- 4 INCR4 -
- 8 INCR8 -
- 16 INCR16 -
- 2, 3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15 INCR Undefined length
WRAP 2 SINGLE Two transfers
- 4 WRAP4 -
- 8 WRAP8 -
- 16 WRAP16 -