Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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ADSP-BF535 Blackfin Processor Hardware Reference 5-11
Data Address Generators
Pre-Modify Stack Pointer Addressing
The only pre-modify instruction in the ADSP-BF535 processor uses the
Stack Pointer register,
SP
. The address in
SP
is decremented by four and
then used as an effective address for the store. The instruction
[ --SP ] = R0
; is used for stack push operations and can support only a
32-bit word transfer.
Indexed Addressing With Immediate Offset
Indexed addressing allows programs to obtain values from data tables,
with reference to the base of that table. The Pointer register is modified by
the immediate field and then used as the effective address. The value of
the Pointer register is not updated.
For example:
P5 = [ P1 + 0x10 ] ;
is an acceptable offset, but
P5 = [ P1 + 0x11 ] ;
causes an alignment exception.

Be sure the offset is divisible by the word-transfer size, measured in
bytes; for example, for a 32-bit transfer, the offset should be a mul-
tiple of 4; for a 16-bit transfer, the offset should be a multiple of 2.
Correct offsets ensure memory alignment.
Post-Modify Addressing
Post-modify addressing uses the value in the Index or Pointer registers as
the effective address and then modifies it by the contents of another regis-
ter. Pointer registers are modified by another Pointer register. Index
registers are modified by a Modify register. This instruction does not sup-
port the Pointer registers as a destination register, nor does it support
byte-addressing.