ST20-C1 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST20-C1' PDF : 205 Pages View PDF
8 Instruction Set Reference
biquad
biquad IIR filter step
Code: 21 F7
Description: Execute a step of a biquad IIR filter on vectors of 16-bit values. Areg
points to the C coefficient vector, Breg points to the X input data vector and Creg
points to the Y results vector. Areg must be word-aligned and Breg and Creg half-
word aligned. biquad increments Breg and Creg by 2 bytes and performs the five
multiply accumulates Y[2] = X[0].C[0] + X[1].C[1] + X[2].C[2] + Y[0].C[3] + Y[1].C[4].
Definition:
if (overflow)
if (Status′underflo w ≠ set ) Status′overflow←set
else if (underflo w)
if (Status′overflow ≠ set ) Status′underflo w←set
else
{
sixteen′[Creg + 4] ← acc >>arith23
Breg′
← Breg + 2
Creg′
← Creg + 2
}
where acc = 1 << 22 + ((sixteen[Areg] << shift) × sixteen[Breg])
+ ((sixteen[Areg+2] << shift) × sixteen[Breg+2])
+ ((sixteen[Areg+4] << shift) × sixteen[Breg+4])
+ ((sixteen[Areg+6] << shift) × sixteen[Creg])
+ ((sixteen[Areg+8] << shift) × sixteen[Creg+2])
– the value of acc is calculated to 48-bit precision
if (Statusmac_scale = 3) shift = 9
else
shift = 4 × Statusmac_scale
Status Register:
May set underflow or overflow.
Comments:
Areg must be word-aligned.
Breg and Creg must be half-word aligned, and must either be both word-aligned
or neither word-aligned.
This instruction may take 8 memory accesses, which will affect interrupt latency.
See also: mac, smacloop, umac
Chapter 5.
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