IMX7D M4 idle mode question

[frankyhsu]

Hi

We are working on the system low power mode. When we disable all I/O in the kernel, we can see M4 will enter the lower power mode The VDD_SOC will have small power consumption. But in real case, we will not have all interface to be off to let the M4 enter the idle mode. Such as that we will still need WiFi module to be active under DTIM mode (no traffic, just link to the server to be connection alive checking). We found we need to remove the SDIO to unload the wifi driver then to enter the M4 low power mode.

So, to let M4 be idle, disable all interface is a mandatory action? How does it implement on Saber board since saber also has muRATA WLAN module?

We see the AN5383, there is the test cases that A7 working but M4 idle (4.3 and 4.4.1).

[igorpadykov]

Hi Franky

if M4 performing some interaction with WiFi module or other activity,

then it can not be put in low power mode. Driver implementation can be

found in sect.4.12 Wi-FI BCM4339 attached Linux Manual. Also as described

in Table 5-5. Low Power Mode Definition i.MX7D Reference Manual

http://cache.nxp.com/files/32bit/doc/ref_manual/IMX7DRM.pdf

M4 (it is in SOC power domain) can be ON/Clock Gated or OFF in lowe power

modes, there are no other options.

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[frankyhsu]

The AN5383 shows the M4 stay in idle mode in section 4.3 and 4.4.1. Why can the M4 stay idle? That's because there is no activity on any I/O bus? M4 should related to all interface I/O pad.

But for 4.3, the SAI should have activity when run audio playback, but the M4 stay M4 idle. I can not understand it.

[igorpadykov]

>. Why can the M4 stay idle? That's because there is no activity on any I/O bus?

yes

>But for 4.3, the SAI should have activity when run audio playback, but the M4 stay M4 idle.

A7 is using SAI and performs audio playback.

Best regards
igor

[frankyhsu]

Since SAI is one of the I/O bus, why does it not impact the M4 to be active at that moment?

[igorpadykov]

because sai is used by A7, not M4.