GR740-UM-DS, Nov 2017, Version 1.7
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GR740
13.4.7.2 AHB master interface
The port contains a single master interface, which is used by both the transmitter and receiver DMA
engines. The arbitration algorithm between the channels is done so that if the current owner requests
the interface again it will always acquire it. This will not lead to starvation problems since the DMA
engines always deassert their requests between accesses.
The burst length is half the AHB FIFO size except for the last transfer of a packet, which might be
smaller. Shorter accesses are also done during descriptor reads and status writes.
The AHB master also supports non-incrementing accesses where the address is constant for several
consecutive accesses. HTRANS is always NONSEQ in this case while for incrementing accesses it is
set to SEQ after the first access. This feature is included to support non-incrementing reads and writes
for RMAP.
If the port does not need the bus after a burst has finished, there is one wasted cycle (HTRANS =
IDLE).
BUSY transfer types are never requested and the port provides full support for ERROR, RETRY and
SPLIT responses.
13.4.8 Registers
The port is programmed through registers mapped into APB address space. The addresses in the table
below are offsets from the base address of each AMBA port. The actual AMBA AHB address used to
access a specific port can be determined by adding the offset to the corresponding base address of the
port, as specified in table 7 in section 2.3. An identical set of registers described in this section exists
for each AMBA port. The used register layout is explained in section 1.11.