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S3C2501X
3.15 COPROCESSOR DATA TRANSFERS (LDC, STC)
The instruction is only executed if the condition is true. The various conditions are defined in Table 3-2. The
instruction encoding is shown in Figure 3-26.
This class of instruction is used to load (LDC) or store (STC) a subset of a coprocessor's registers directly to
memory. ARM9TDMI is responsible for supplying the memory address, and the coprocessor supplies or accepts
the data and controls the number of words transferred.
31
28
27
Cond
3.15.1 THE COPROCESSOR FIELDS
The CP# field is used to identify the coprocessor which is required to supply or accept the data, and a
coprocessor will only respond if its number matches the contents of this field.
The CRd field and the N bit contain information for the coprocessor which may be interpreted in different ways by
different coprocessors, but by convention CRd is the register to be transferred (or the first register where more
than one is to be transferred), and the N bit is used to choose one of two transfer length options. For instance N =
0 could select the transfer of a single register, and N = 1 could select the transfer of all the registers for context
switching.
25
24
23
22
21
20
19
110
P U
N
W
L
[7:0] Unsigned 8 Bit Immediate Offset
[11:8] Coprocessor Number
[15:12] Coprocessor Source/Destination Register
[19:16] Base Register
[20] Load/Store Bit
0 = Store to memory
1 = Load from memory
[21] Write-back Bit
0 = No write-back
1 = Write address into base
[22] Transfer Length
[23] Up/Down Bit
0 = Down: subtract offset from base
1 = Up: add offset to base
[24] Pre/Post Indexing Bit
0 = Post: add offset after transfer
1 = Pre: add offset bofore transfer
[31:28] Condition Field
Figure 3-26. Coprocessor Data Transfer Instructions
16
15
12
11
Rn
CRd
INSTRUCTION SET
8 7
CP#
Offset
0
3-53
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