COBHAM GR740 User Manual

GR740-UM-DS, Nov 2017, Version 1.7 386 www.cobham.com/gaisler
GR740
In case of an ERROR response on the master side the ERROR response will be given for the same
access (address) on the slave side. SPLIT and RETRY responses on the master side are re-attempted
until an OKAY or ERROR response is received.
32.2.3 AHB write transfers
The AHB/AHB bridge implements posted writes. Writes are accepted with zero wait states if the
bridge is idle. During the AHB write transfer on the slave side the data is buffered in the internal write
FIFO and the transfer is completed on the slave side by always giving an OKAY response. The master
interface requests the bus and performs the write transfer when the master bus is granted. If the burst
transfer crosses the 32-byte write burst boundary, a SPLIT response is given. When the bridge has
written the contents of the FIFO out on the master side, the bridge will allow the master on the slave
side to perform the remaining accesses of the write burst transfer.
32.2.4 Read and write combining
Read and write combining allows the bridge to assemble or split AMBA accesses from the Debug
AHB bus into one or several accesses on the Processor AHB bus. This functionality can improve bus
utilization and also allows cores that have differing AMBA access size restrictions to communicate
with each other. The effects of read and write combining is shown in the table below.
Read and write combining is disabled for accesses to the area 0xF0000000 - 0xFFFFFFFF to prevent
accesses wider than 32 bits to register areas.
Table 516.Read and write combining
Access on slave interface Resulting access(es) on master interface
BYTE or HALF-WORD single read
access to any area
Single access of same size
BYTE or HALF-WORD read burst to
prefetchable area
Incremental read burst of same access size as on slave interface, the
length is the same as the number of 32-bit words in the read buffer, but
will not cross the read burst boundary.
BYTE or HALF-WORD read burst to
non-prefetchable area
Incremental read burst of same access size as on slave interface, the
length is the same as the length of the incoming burst. The master
interface will insert BUSY cycles between the sequential accesses.
BYTE or HALF-WORD single write Single access of same size
BYTE or HALF-WORD write burst Incremental write burst of same size and length, the maximum length
is the number of 32-bit words in the write FIFO.
Single read access to any area Single access of same size
Read burst to prefetchable area Burst of 128-bit up to 32-byte address boundary.
Read burst to non-prefetchable area Incremental read burst of same access size as on slave interface, the
length is the same as the length of the incoming burst. The master
interface will insert BUSY cycles between the sequential accesses.
Single write Single write access of same size
Write burst Burst write of maximum possible size. The bridge will use the maxi-
mum size (up to 128-bit) that it can use to empty the writebuffer.

COBHAM GR740 Specifications

General

Brand	COBHAM
Model	GR740
Category	Computer Hardware
Language	English