GR740-UM-DS, Nov 2017, Version 1.7
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GR740
13.4.6.5 RMW commands
All read-modify-write sizes are supported except of 6 which would cause 3 B being read and written
on the bus. The RMW bus accesses have the same restrictions as the verified writes. As in the verified
write case, the incrementing bit can be set to any value since only one AHB bus operation is per-
formed for each RMW command. Too large cargo can only be detected after bus accesses and the
detection of this error condition can therefore not prevent the operation from being performed. No
data is sent in a reply if an error is detected, i.e. if the status field is non-zero.
13.4.6.6 Control
The RMAP target mostly runs in the background without any external intervention but there are a few
control possibilities.
There is an enable bit in the control register of the port which can be used to completely disable the
RMAP target. When it is set to ‘0’, no RMAP packets are handled in hardware but are instead stored
to the DMA channel.
There is a chance that RMAP commands are not executed in the order of their arrival. This can hap-
pen if a read command arrives before one or more write commands. Since the target stores replies in a
buffer with more than one entry, several commands can be processed before a reply is sent out. Data
for read replies is read when the reply is transmitted and thus write commands that arrived after the
read command might have be already processed by then if a congestion on the transmit side prevented
the RMAP target from sending out the reply immediately. To avoid this situation, the RMAP buffer
disable bit can be set to force the target to only use one buffer.
The last control option for the target is the possibility to set the destination key, which is found in a
separate register.
Table 153.
AMBA port hardware RMAP handling of different packet type and command fields.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Command
Action
Reserved
Command
/ Response
Write /
Read
Verify
data
before
write
Acknow-
ledge
Increment
Address
0
0
-
-
-
-
Response
Stored to DMA-channel.
0
1
0
0
0
0
Not used
Does nothing. No reply is sent.
0
1
0
0
0
1
Not used
Does nothing. No reply is sent.
0
1
0
0
1
0
Read single
address
Executed normally. Address has
to be word aligned and data size
a multiple of four. Reply is sent.
If alignment restrictions are vio-
lated error code is set to 10.
0
1
0
0
1
1
Read incre-
menting
address.
Executed normally. No restric-
tions. Reply is sent.
0
1
0
1
0
0
Not used
Does nothing. No reply is sent.
0
1
0
1
0
1
Not used
Does nothing. No reply is sent.
0
1
0
1
1
0
Not used
Does nothing. Reply is sent with
error code 2.