Re: backup/restore concept?

[Nishanth Menon <nm@ti.com>]

On 07/24/2013 12:49 AM, Viresh Kumar wrote:
> Adding more relevant list in cc.
>
> On 23 July 2013 16:05, Ryan <ryanphilips19@googlemail.com> wrote:
>> Hi,
>>
>> I have some doubts on backup and restore operation. From what i understand:
>>
>> We copy all registers values & addresses of all controllers in the SOC
>> to the internal RAM or SRAM.
>> before we put CPU to sleep?
>>
>> I want to know if we also copy the code segment into SRAM and what
>> happens after wakeup.
>> If so, where exactly we need to copy and how cpu jumps here after
>> wakeup. or is there any other mechanism
>> that is used. What executes first since DDR is in self-refresh.
>>
>> I use OMAP4 and this is my understanding. I could not understand much
>> other than in OFF mode
>> all the controller registers get copied to SRAM. Does anything else
>> also gets copied too?
>> or am i missing any basics here.
This understanding is not accurate. OMAP behavior for "OFF mode" is as 
follows (as part of suspend/resume):
- drivers do their own "context save" - saving of registers based on 
their need.
- SAR registers are saved (note - this is *not* every possible register 
on OMAP - but a core subset).
- cpu goes to WFI triggering h/w statemachine flow. (wfi instruction is 
in DDR)
    - as part of "OFF mode" DDR is put into self refresh automatically 
by memory controller.

on wakeup
- core registers are restored by hardware
- DDR is brought out of selfrefresh,
- execution resume in resume function pointer
- drivers restore their own modules as needed.

So, there is no real black magic here :)

-- 
Regards,
Nishanth Menon