CS494002 datasheet(76/100 Pages) CIRRUS

76 / 100 page

a list of all pertinent configuration messages.

Writing the KICKSTART message to DSPAB

begins the audio decode process.

9. SOFT RESETTING THE CS49400

Soft resetting the CS49400 uses a combination of

software and hardware. This method of resetting

the DSP is usually referred to as a “soft reset” even

though it involves toggling the reset pin due to the

fact that a soft reset message is sent to the DSP. To

soft reset the device, a previous application code

must have been downloaded without power cycling

the DSP. Figure 54, "Host Controlled Master

Softreset" on page 77 describes the soft reset

procedure. The main purpose behind a soft reset is

to take advantage of the fact that all AC-3 based

codes can accept both AC-3 compressed data as

well as PCM data. This allows for a the host to

reconfigure the AC-3 application code for PCM or

AC-3 without having to completely redownload the

same application code.

9.1 Host Controlled Master Soft Reset

This reset procedure is used to restart the

application code that has already been loaded on

the DSP. All writes and reads with the CS49400

should follow the protocol given in Section 8

“Boot Procedure” on page 71.

1) A Soft Reset sequence is started when the host

holds the mode pins appropriately (UHS[2:0]

and FHS[1:0]) and toggles RESET.

2) The host must send the C_SOFT_RESET

message to DSPC. This causes the application

code on DSPAB and DSPC to reset and allow

the downloaded application to run.

3) If the soft reset was successful, DSPC sends out

a C_APP_START message the host can

proceed to step 4. If DSPC does not send an the

application start message, the host must re-try

the whole procedure again.

4) The host can send hardware and software

configuration messages for DSPC.

5) At this point the application code on DSPC is

running and the host needs to configure

DSPAB.

6) Next the host must wait for FINTREQ to go

low and read the AB_APP_START message

from DSPAB. If DSPAB does not send an the

application start message the host must re-try

the whole procedure again, beginning from step

7) The host must send hardware and software

configuration messages for DSPAB.

8) At this point the application code on DSPAB is

running.

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