[U-Boot] [PATCH 2/4] nds32/ag102: add ag102 soc support

[Macpaul Lin]

Hi Mike,

2011/11/29 Macpaul Lin <macpaul at gmail.com>

> Hi Mike,
>
>
This reply didn't CC to u-boot mailing list.
So I forward it again.


> 2011/11/24 Mike Frysinger <vapier at gentoo.org>
>
>> On Tuesday 22 November 2011 21:16:50 Macpaul Lin wrote:
>> > 2011/11/19 Mike Frysinger <vapier at gentoo.org>
>> > > > +.globl       turnoff_watchdog
>> > > > +turnoff_watchdog:
>> > > > +
>> > >
>> > > can't this be C code ?
>> >
>> > This is because after reset, the watchdog might be enabled if there is
>> > another boot loader has ran before u-boot.
>> > If the other boot loader enabled watchdog but didn't stop it,
>> > it might cause u-boot to be reset during assembly initialization phase.
>> > So we need to disable watchdog here.
>>
>>
> The initialize procedure of NDS32 N1213 CPU is mentioned as follows.
>
> 1st, we set correct vector size in the system registers inside the cpu to
> make sure the
> vector table works well.
> 2nd, do dram/ddr dram controller initialize since there are no memory like
> SRAM on
> SoC could be able to used as stack.
> 3rd, do this watchdog disable to prevent the continuous boot strap will be
> interrupted by
> hardware reset due to watchdog timeout.
> 4th, do small stack setup to prepare C environment which based on step
> No.2, dram/ddr
> controller initialize. With out this memory initialization, the C stack
> couldn't be initialized
> and board_init_f() cannot be executed.
>
> Of course you can do disable watchdog timer later inside board_init_f(),
> but we're afraid
> of to increase the probability of boot up fail caused by watchdog reset.
>
>
>>  my point is, why can't turnoff_watchdog() be written in C ?  why does
>> this func
>> need to be written in assembly ?
>>
>> looking at the start.S, seems like there's a bit of logic there that
>> should be
>> in C and not a lot of asm.  *shrug* too late now i guess.
>> -mike
>>
>
> Which left in start.S included the copy loop for relocation, and .got,
> .bss fixup.
> Others are vectors and I/D cache operation if you want to use in
> board_init_f().
> Please give us your idea and see if this will be better.
>
> Thanks!
>

Thanks.

-- 
Best regards,
Macpaul Lin