Cirrus Logic AN298 - Manual (Page 27)

AN298RC14 27
7 Low Power Mode
7 Low Power Mode
Note: The Low Power Mode section will be moving to the CS485xx Hardware User’s Manual in the next revision of that
manual.
The CS485xx has a low power mode to enable power savings when not in use. Low power mode is entered during the
softboot procedure.
7.1 Low Power Mode Messaging
One message is relevant to the low power mode procedure for the CS485xx. This message is SOFTBOOT_LP. The host
must read any ACK and prior messages before low power mode may commence.
7.2 Low Power Mode Steps
1. The system controller should send the SOFTBOOT_LP message (0x81000009 0x00000011).
2. The CS485xx is now in low power mode.
3. To test that the CS485xx 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 their state
can be checked to verify low power mode is active.
7.3 Getting 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: This 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 7-1 .
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 message.
Mnemonic Value
SOFTBOOT_LP 0x81000009
0x00000011