Dram retention mode

[abdrhmn]

Hi,

I am working on imx8ulp power optimization.

I am interested to know more on the dram_enter_retention mode and dram_exit_retention mode.

1) Other than observing the current usage, How to know that it is already in retention mode? 

2) Is the retention mode only work in shared ram?

3) If calling the retention mode causing the system hang, what would be the culprit?

4) If calling the dram_exit_retention mode causing the current a bit higher (than before calling it), what is the reason?

Thanks!

[abdrhmn]

Hi,

If the system I'm working on using lpddr. How can I make this work?

[Zhiming_Liu]

Hello,

The functions in plat/imx/imx8ulp/dram.c(imx-atf) have been done for different DRAMs, LPDDR4 & LPDDR3. There are still some spaces to optimize power consumption, please refer  AN13951 

Best Regards,
Zhiming

[abdrhmn]

Hi,

I recently trying the API that you provided in the SDK (board.c)

The test is quite simple. 

1) Create a timer about 30s
2) Call BOARD_DramEnterRetention + WFI()
3) when timer expired, trigger the interrupt and call BOARD_DramExitRetention()

I could see some current changes when in retention mode. However, it seems not able to exit.

May I know why when calling BOARD_DramExitRetention(), the A core is not wake up and the M Core is dead?

[Zhiming_Liu]

Hello,

To test Dram retention and exit, please use power_mode_switch demo and refer the api in power_mode_switch.c.

Best Regards,
Zhiming

[Zhiming_Liu]

Hello,
Q1: Other than observing the current usage, How to know that it is already in retention mode? 

-->There is no other way to make observations, these functions are tested and there is no need to worry about it not being triggered correctly.

Q2: Is the retention mode only work in shared ram?

-->Yes

Q3: If calling the retention mode causing the system hang, what would be the culprit?

-->Have you made any changes to the code for this feature?

Q4 : If calling the dram_exit_retention mode causing the current a bit higher (than before calling it), what is the reason?

-->dram_exit_retention will recover DDR clocks and enable DDR PHY, so the current going to high is reasonable

Best Regards,
Zhiming