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Special Filter Instructions
4-64
Any combination of registers different from the above will yield incorrect
results with the FIR/COR instruction.
Use R5 to
wrap around
R0
0x010
0x0100
0x0106
0x0102
x[k] x[k–1]
x[k–2]x[k–3]
tag
After FIR/COR execution
The STAT register is saved in the filterSTAT_tag location. The output of the fil-
tering operation in the example is located in AC0 (lower word) and AC1 (high
word). This 32 bit result is stored in the SampleOut RAM location. R0 should
be pointing to the oldest sample. The oldest sample, x[k–3], is overwritten
by the next sample to be filtered, x[k+1]. R0 is saved in the startOfBuff
pointer for the next FIR/COR instruction
Notice that R0 points backwards by one location from its starting point each
time an FIR/COR instruction is executed. In the above figure, R0 would end
up at successive locations in a clockwise manner.