ADAU1761BCPZ-R7 datasheet(46/92 Pages) AD

46 / 92 page

Data Sheet

ADAU1761

PROGRAM RAM, PARAMETER RAM, AND DATA RAM

analog.com

Rev. F | 46 of 92

Table 27. Parameter RAM Read/Write Format (Single Address)

Byte 0

Byte 1

Byte 2

Byte 3

Bytes[4:6]

chip_adr[6:0], R/W

param_adr[15:8]

param_adr[7:0]

0000, param[27:24]

param[23:0]

Table 28. Parameter RAM Block Read/Write Format (Burst Mode)

Byte 0

Byte 1

Byte 2

Byte 3

Bytes[4:6]

Bytes[7:10]

Bytes[11:14]

chip_adr[6:0], R/W

param_adr[15:8]

param_adr[7:0]

0000, param[27:24]

param[23:0]

<—param_adr—>

param_adr + 1

param_adr + 2

Table 29. Program RAM Read/Write Format (Single Address)

Byte 0

Byte 1

Byte 2

Bytes[3:7]

chip_adr[6:0], R/W

prog_adr[15:8]

prog_adr[7:0]

prog[39:0]

Table 30. Program RAM Block Read/Write Format (Burst Mode)

Byte 0

Byte 1

Byte 2

Bytes[3:7]

Bytes[8:12]

Bytes[13:17]

chip_adr[6:0], R/W

prog_adr[15:8]

prog_adr[7:0]

prog[39:0]

<—prog_adr—>

prog_adr + 1

prog_adr + 2

SOFTWARE SAFELOAD

To update parameters in real time while avoiding pop and click

noises on the output, the ADAU1761 uses a software safeload

mechanism. The software safeload mechanism enables the Sig-

maDSP core to load new parameters into RAM while guaranteeing

that the parameters are not in use. This prevents an undesirable

condition where an instruction could execute with a mix of old and

new parameters.

SigmaStudio sets up the necessary code and parameters automati-

cally for new projects. The safeload code, along with other initializa-

tion code, fills the first 39 locations in program RAM. The first eight

parameter RAM locations (Address 0x0000 to Address 0x0007) are

configured by default in SigmaStudio as described in Table 31.

Table 31. Software Safeload Parameter RAM Defaults

Address (Hex)

Function

0x0000

Modulo RAM size

0x0001

Safeload Data 1

0x0002

Safeload Data 2

0x0003

Safeload Data 3

0x0004

Safeload Data 4

0x0005

Safeload Data 5

0x0006

Safeload target address (offset of −1)

0x0007

Number of words to write/safeload trigger

Address 0x0000, which controls the modulo RAM size, is set by

SigmaStudio and is based on the dynamic address generator mode

of the project.

Parameter RAM Address 0x0001 to Address 0x0005 are the five

data slots for storing the data to be safeloaded. The safeload

parameter space contains five data slots by default because most

standard signal processing algorithms have five parameters or less.

Address 0x0006 is the target address in parameter RAM (with an

offset of −1). This designates the first address to be written. If more

than one word is written, the address increments automatically for

each data-word. Up to five sequential parameter RAM locations

can be updated with safeload during each audio frame. The target

address offset of −1 is used because the write address is calculated

relative to the address of the data, which starts at Address 0x0001.

Therefore, to update a parameter at Address 0x000A, the target

address is 0x0009.

Address 0x0007 designates the number of words to be written into

the parameter RAM during the safeload. A biquad filter uses all five

safeload data addresses. A simple mono gain cell uses only one

safeload data address. Writing to Address 0x0007 also triggers the

safeload write to occur in the next audio frame.

The safeload mechanism is software based and executes once per

audio frame. Therefore, system designers must take care when

designing the communication protocol. A delay equal to or greater

than the sampling period (the inverse of sampling frequency) is

required between each safeload write. A sample rate of 48 kHz

equates to a delay of at least 21 μs. If this delay is not observed,

the downloaded data is corrupted.

SOFTWARE SLEW

When the values of signal processing parameters are changed

abruptly in real time, they sometimes cause pop and click sounds

to appear on the audio outputs. To avoid pops and clicks, some

algorithms in SigmaStudio implement a software slew functionality.

Algorithms using software slew set a target value for a parameter

and continuously update the value of that parameter until it reaches

the target.

The target value takes an additional space in parameter RAM, and

the current value of the parameter is updated in the non-modulo

section of data RAM. Assignment of parameters and nonmodulo

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