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eciwx
Assembler Syntax
BIT
0
1
2
FIELD
31
BIT
16
17
18
FIELD
B
Definition
Operation
Description
MOTOROLA
eciwx
rD,rA,rB
3
4
5
6
7
19
20
21
22
23
External Control In Word Indexed
if rA = 0 then b ← 0
else
b← (rA)
EA ← b + (rB)
paddr ← address translation of EA
send load word request for paddr to device identified by
EAR[RID]
rD ← word from device
The eciwx instruction allows the system designer to map special
devices in an alternative way. The MMU translation of the EA is
not used to select the special device, as it is used in most
instructions such as loads and stores. Rather, it is used as an
address operand that is passed to the device over the address
bus. Four other pins (the burst and size pins on the 60x bus) are
used to select the device; these four pins output the 4-bit
resource ID (RID) field that is located in the EAR register. The
eciwx instruction also loads a word from the data bus that is
output by the special device.
The eciwx 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 load word request for the physical address (referred to as real
address in the architecture specification) corresponding to EA is
sent to the device identified by EAR[RID], bypassing the cache.
The word returned by the device is placed in rD. EAR[E] must be
1. If it is not, a DSI exception is generated.
MPC823e REFERENCE MANUAL
MPC823e Instruction Set—eciwx
8
9
10
11
12
D
24
25
26
27
28
310
13
14
15
A
29
30
31
0
B-53
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