P60ARM-B Zarlink Semiconductor, Inc., P60ARM-B Datasheet - Page 59

• Manufacturer Part Number: P60ARM-B
• Description: 32-bit RISC microprocessor
• Manufacturer: Zarlink Semiconductor, Inc.

4.12.2 Addressing modes
ARM60 is responsible for providing the address used by the memory system for the transfer, and the
addressing modes available are a subset of those used in single data transfer instructions. Note, however,
that the immediate offsets are 8 bits wide and specify word offsets for coprocessor data transfers, whereas
they are 12 bits wide and specify byte offsets for single data transfers.
The 8 bit unsigned immediate offset is shifted left 2 bits and either added to (U=1) or subtracted from (U=0)
the base register (Rn); this calculation may be performed either before (P=1) or after (P=0) the base is used
as the transfer address. The modified base value may be overwritten back into the base register (if W=1), or
the old value of the base may be preserved (W=0). Note that post-indexed addressing modes require
explicit setting of the W bit, unlike LDR and STR which always write-back when post-indexed.
The value of the base register, modified by the offset in a pre-indexed instruction, is used as the address for
the transfer of the first word. The second word (if more than one is transferred) will go to or come from an
address one word (4 bytes) higher than the first transfer, and the address will be incremented by one word
for each subsequent transfer.
4.12.3 Address Alignment
The base address should normally be a word aligned quantity. The bottom 2 bits of the address will appear
on A[1:0] and might be interpreted by the memory system.
4.12.4 Use of R15
If Rn is R15, the value used will be the address of the instruction plus 8 bytes. Base write-back to R15 shall
not be specified.
4.12.5 Data aborts
If the address is legal but the memory manager generates an abort, the data trap will be taken. The write-
back of the modified base will take place, but all other processor state will be preserved. The coprocessor is
partly responsible for ensuring that the data transfer can be restarted after the cause of the abort has been
resolved, and must ensure that any subsequent actions it undertakes can be repeated when the instruction
is retried.
The state of the LATEABT control signal does not affect the behaviour of LDC and STC instructions in the
event of an Abort exception.
4.12.6 Instruction Cycle Times
Coprocessor data transfer instructions take (n-1)S + 2N + bI incremental cycles to execute, where S, N and
I are as defined in section 5.1 Cycle types on page 65.
n
b
4.12.7 Assembler syntax
<LDC|STC>{cond}{L} p#,cd,<Address>
is the number of words transferred.
is the number of cycles spent in the coprocessor busy-wait loop.
Instruction Set - LDC, STC
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