AM3358: Deep sleep without RTC

Aaron Spaete

Part Number: AM3358

Team,

My customer has the following question.

We are trying to use the deep sleep mode in the AM3358. We ran across a possible issue because we aren’t using the RTC and it is removed from use in the u-boot and kernel.

It seems that the deep sleep functionality uses one of the RTC registers to store some data that can be restored when returning from deep sleep. This seems to be an undocumented usage of that register. The data doesn’t seem critical and not saving it off seems like that should work, but we don’t return from sleep.

The question is

how do we use the processor deep sleep functionality without the RTC (without access to that register)?

Are there any application notes regarding this?

Thanks,

Aaron

over 3 years ago

0 Bin Liu over 3 years ago

TI__Guru**** 178311 points

Hi Aaron,

I am not aware of such application notes. Do you have details of this mentioned RTC register? which offset is it?

0 Aaron Spaete over 3 years ago in reply to Bin Liu

TI__Expert 4637 points

Bin,

RTC_SCRATCH0_REG (offset 0x60) is used basic PM operations (PM start and end) in "drivers/soc/ti/pm33xx.c. pm33xx.c" implements the SOC-specific operations.
The start function doesn't put a problem but "am33xx_pm_end" reads RTC_SCRATCH0_REG register unconditionally:

static void am33xx_pm_end(void)
{
u32 val = 0;
struct nvmem_device *nvmem;

nvmem = devm_nvmem_device_get(&omap_rtc->dev, "omap_rtc_scratch0");
m3_ipc->ops->finish_low_power(m3_ipc);
if (rtc_only_idle) {
if (retrigger_irq)

Regards,

Aaron

0 Bin Liu over 3 years ago in reply to Aaron Spaete

TI__Guru**** 178311 points

Hi Aaron,

Which kernel version does the customer use?

The condition check in am33xx_pm_end() has been added in Processor SDK v7.0 in 2019:

https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/commit/?h=linux-5.4.y&id=d8e0cecbcaf09f38661bfb7da4c1e62297308672

0 Aaron Spaete over 3 years ago in reply to Bin Liu

TI__Expert 4637 points

Bin,

Clarification to be clear with what you are saying.

In the kernel version 5.4 the check that was added requires the use of the scratch register, is that correct?

So with the update, RTC is required to use deep sleep functionality?

Can you do deep sleep without RTC?

Regards,

Aaron

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AM3358: Deep sleep without RTC