STA382BW datasheet(163/172 Pages) STMICROELECTRONICS

163 / 172 page

STA382BW

Doc ID 022783 Rev 1

163/172

The STA382BW implements an automatic CRC computation for the biquad and

MDRC/XOver coefficient memory. Memory cell contents from address 0x00 to 0x27 will be

bit XORed to obtain the BQCHKE checksum, while cells from 0x28 to 0x31 will be XORed to

obtain the XCCHKE checksum. Both checksums (24-bit wide) are exported on I2C registers

from 0x60 to 0x65. The checksum computation will start as soon as the BCGO (for biquad

RAM bank) or the XCGO bit (for MDRC/XOver coefficients) is set to 1. The checksum is

computed at the processing sample rate if the IR bits equal “01” or “10”, otherwise the

checksum is computed to half the processing sample rate.

When BCCMP or XCCMP are set to ‘1’, the relative checksum (BQCHKE and XCCHKE) is

continuously compared with BQCHKR and XCCHKR respectively. If the checksum matches

its own reference value, the respective result bits (BCRES and XCRES) will be set to ‘0’.

The compare bits have no effect if the respective GO bit is not set.

In case of checksum errors (i.e. the internally computed didn’t match the reference), an

automatic device reset action can be activated. This function is enabled when the BCAUTO

or XCAUTO bit is set to ‘1’. The automatic reset bits have no effect if the respective compare

bits are not set.

The recommended procedure for the automatic reset activation is the following:

●

Download the set of coefficients (RAM locations 0x00…0x27)

●

Download the externally computed biquad checksum into registers BQCHKR

●

Enable the checksum of the biquad coefficients by setting the BCGO bit. The

checksum will start to be automatically computed by the STA382BW and its value

exposed on registers BQCHECKE. The checksum value is computed and updated.

●

Enable the checksum comparison by setting the BCCMP bit. The internally computed

checksum will start to be compared with the reference one and the result will be

exposed on the BCRES bit. The following operation will be executed on each audio

frame:

if ((BQCHKE == BQCHKR))

{

BC_RES = 0;// Checksum is ok, reset the error bit

}

else

{

BC_RES = 1;// Checksum error detected, set the error bit

}

●

Wait until the BCRES bit goes to 0, meaning that the checksum result bit has started to

be updated and everything is ok. Time-out of this operation (e.g. > 1 ms) will indicate

checksum failure, and the MCU will handle this event.

●

Enable automatic reset of the device in case of checksum error by setting the BCAUTO

bit. The BCRES bit will then be automatically checked by the STA382BW, on each

audio frame, and the reset event will be triggered in case of checksum mismatch.

●

Periodically check the BC_RES status. A value of 1 indicates that a checksum

mismatch has occurred and, therefore, the device went through a reset cycle.

The previous example is intended for biquad CRC bank calculation, but it can be easily

extended to MDRC/XOver CRC computation.

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