ST20-C1 datasheet(95/205 Pages) STMICROELECTRONICS

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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

× Status

mac_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.

ST20-C1 Datasheet(PDF) 95 Page - STMicroelectronics

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