ST20-C1 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST20-C1' PDF : 205 Pages View PDF
5.4 Biquad IIR filter
mac_buffer
0
1
2
3
4
5
6
7
Buffer size
(data items)
infinite
4
8
16
32
64
128
256
Buffer size
(bytes)
infinite
8
16
32
64
128
256
512
Table 5.4 mac_buffer coding
5.3.3 Scaling
Scaling of the input data in the X vector is controlled by the mac_scale field of the
status register, as described in section 5.6.
5.3.4 Accumulator format mode
smacloop supports two data formats for the initial and final accum ulator value. If
mac_mode is 0 then Q15 (sign extended to 32 bits) is used, and the mode is said to
be ShortMode. If mac_mode is 1 then Q31 is used, and the mode is said to be
LongMode.
5.4 Biquad IIR filter
The biquad instruction performs a fixed sequence of 5 multiply-accumulates. Figure
5.1 shows an example using Q14 format. The parameters to the instruction are
pointers to three vectors of 16-bit values:
• an X input data vector,
• a Y results vector and
• a coefficient vector C. This vector must be word-aligned.
biquad calculates the next item in the Y vector according to the following formula, and
writes this to memory, incrementing the X and Y pointers by two bytes:
Y[2] =
X[0].C[0] + X[1].C[1] + X[2].C[2] + Y[0].C[3] + Y[1].C[4]
The X and Y vectors must be either both word-aligned or neither word-aligned.
The C pointer is left unchanged. This allows successive biquad instructions to be
executed back-to-back to generate a set of filter outputs with no additional overhead.
biquad scales the X input data according to the mac_scale field of the status register,
as described in section 5.6. The mac_scale field ma y be set using smacinit, as
described in section 5.3.
58/205
®
Share Link: 
