ST20-C1 datasheet(56/205 Pages) STMICROELECTRONICS

56 / 205 page

5.1 Data formats

56/205

Multiply accumulate

This section describes the multiply-accumulate instructions and their use. All these

instructions are described in the context of their intended use. Instructions for general

use (arithmetic, loading, storing etc.) are described in Chapter 4. Instructions for

exceptions are described in Chapter 6 and multi-tasking instructions are described in

Chapter 7. The architecture of the ST20-C1, including the registers and memory

arrangement, is described in Chapter 3.

Multiply accumulate operations are provided by the signal processing instructions

listed in Table 5.1.

5.1

Data formats

A signed fractional number of

N bits is described as x.y, where x+y=N. This means the

number is made up from

x bits before the binary point, an implied binary point, and y

fractional bits. More details of the data formats are given in section 5.7.

5.2

mac and umac

mac and umac are general purpose multiply accumulate instructions, multiplying two

32-bit values and adding them to a 32-bit unsigned initial accumulator, giving a 64-bit

accumulator.

mac treats the multiplicands as signed and umac treats them as

unsigned. Initially Areg and Breg hold the values to be multiplied and Creg holds the

initial accumulator. On completion, Areg is the least significant word of the result

accumulator, Breg the most significant and Creg holds a copy of the initial Areg.

5.3

Short multiply accumulate loop

The

smacloop instruction performs a multiply-accumulate operation on two vectors of

16-bit values held in memory. It takes an initial accumulator value and two pointers,

one to each of two data vectors.

• The X vector of data values is normally considered to reside within a circular

buffer of programmable size, but this can be turned off. When data fetches

reach the end of this buffer, the pointer wraps-around back to the start of the

buffer and continues. The X vector must be word aligned.

• The Y vector of coefficients is always in a flat address space , and never wraps

around. The Y vector must be half-word aligned.

Mnemonic

Name

mac

multiply accumulate

umac

unsigned multiply accumulate

smacinit

initialize short multiply accumulate loop

smacloop

short multiply accumulate loop

biquad

biquad IIR filter step

Table 5.1 Multiply accumulate instructions

ST20-C1 Datasheet(PDF) 56 Page - STMicroelectronics

ST20-C1 Datasheet(HTML) 56 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Descarga

Enlace URL