Cirrus Logic CS485xx - Manual (Page 30)

Low Power Mode
CS485xxr Hardware User’s Manual
DS734UM7 Copyright 2009 Cirrus Logic, Inc. 2-12
2.6 Low Power Mode
The CS485xx has a low power mode to enable power savings when not in use. Low power mode is
entered during the softboot procedure.
2.6.1 Low Power Mode Messaging
One message is relevant to the low power mode procedure for the CS48xxxx. This message is
SOFTBOOT_LP.
The host must read any ACK and prior messages before low power mode may commence.
2.6.2 Getting into Low Power Mode
Follow these steps to get into low power mode:
1. The system controller should send the SOFTBOOT_LP message (0x81000009 0x00000011).
2. The CS48xxxx is now in low power mode.
3. To test that the CS48xxxx is in low power mode the host controller can send a message and verify
that there is no response. Additionally all the GPIO pins will be set to inputs in low power mode
with weak pull-ups so there state can be checked to verify low power mode is active.
2.6.3 Getting Out of Low Power Mode
Follow these steps to get out of low power mode:
1. Set DSP_RESET low.
2. Set DSP_RESET high.
3. Send the SLAVE_BOOT message (0x80000000).
4. Read the BOOT_START message (0x00000001).
5. Send the WAKEUP_*.ULD file.
Note: “*” .uld name is dependent on the current memory configuration. For example: if loading
os_48520_p2_*.uld, then send wakeup_p2.uld. If loading os_48520_p4_*.uld, then send wakeup_p4.uld,
and so forth. See
Table 2-8 .
6. Read the BOOT_SUCCESS message (0x00000002).
7. Send the SOFT_RESET message (0x40000000).
8. Read the APP_START message (0x00000004).
9. Send Hardware Configuration messages.
10.Send Software Configuration messages.
11.Send the KICKSTART messages.
Figure 2-6 shows a flowchart of the steps used to exit Low Power mode.
Mnemonic Value
SOFTBOOT_LP
0x81000009
0x00000011