
MPC823 Instruction Set—ecowx
MOTOROLA
MPC823 USER’S MANUAL
B-55
INSTRUCTION
SET
B
ecowx
Assembler Syntax
ecowx
rS,rA,rB
Definition
External Control Out Word Indexed
Operation
if rA = 0 then b
← 0
else
b
← (rA)
EA
← b + (rB)
paddr
← address translation of EA
send store word request for paddr to device identified by
EAR[RID]
send rS to device
Description
The ecowx instruction and the EAR register can be very efficient
when mapping special devices such as graphics devices that
use addresses as pointers.
EA is the sum (rA|0) + (rB). A store word request for the physical
address corresponding to EA and the contents of rS are sent to
the device identified by EAR[RID], bypassing the cache. EAR[E]
must be 1, if it is not, a DSI exception is generated. EA must be
a multiple of four. If it is not, one of the following occurs:
A system alignment exception is generated.
A DSI exception is generated (possible only if EAR[E] = 0).
The results are boundedly undefined.
The ecowx instruction is supported for effective addresses that
reference memory segments in which SR[T] = 0, and for EAs
mapped by the DBAT registers. If the EA references a direct-
store segment (SR[T] = 1), either a DSI exception occurs or the
results are boundedly undefined. However, note that the direct-
store facility is being phased out of the architecture and will not
likely be supported in future devices. Thus, software should not
depend on its effects.
BIT
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
FIELD
31
S
A
BIT
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
FIELD
B
438
0