[U-Boot] [RFC PATCH 0/1] SPL JTAG boot mode

[Ezra Savard]

> -----Original Message-----
> From: Michal Simek [mailto:michal.simek at xilinx.com]
> Sent: Monday, August 11, 2014 6:30 AM
> To: Tom Rini; Michal Simek
> Cc: u-boot at lists.denx.de; Stephen Warren; Ezra Savard; Soren
> Brinkmann; Roger Quadros
> Subject: Re: [U-Boot] [RFC PATCH 0/1] SPL JTAG boot mode
>
> On 08/11/2014 03:17 PM, Tom Rini wrote:
> > On Mon, Aug 11, 2014 at 03:03:35PM +0200, Michal Simek wrote:
> >
> >> Hi,
> >>
> >> I have got this patch some time ago but I am not still 100% sure
> >> about use case. Anyway Soren uses this mode that's why let me send
> >> this patch and we can discuss if this can be useful for someone
> >> else too.
> >>
> >> The use case is to load U-Boot SPL to do init HW and then load
> >> images via JTAG because RAM is initialized and then run full u-boot.
> >> There is an option to do HW initialization without U-Boot SPL but
> >> there are some differences and it is just better to directly use
> >> code which will run on the board when everything is tested.
> >
> > So in this case, you attach JTAG to the board, halt on reset, reset
> > the board.  JTAG load in SPL and fiddle memory so that
> > BOOT_DEVICE_JTAG is set, let SPL run,
>
> BOOT_DEVICE_JTAG for zynq case will be setup in spl_boot_device()
> based on dip-switch boot mode setup read from SLCR.
>
> > halt when you see the print (or set a breakpoint for that part,
> > either way), then load U-Boot via JTAG, resume over the while loop,
> > and then debug U-Boot as needed?
>
> In general that's my impression how Soren uses it.
> I would let him to confirm that this is his use case.
>
> Not sure if he is just loading images when cpu is in while(1) loop and
> let u- boot spl continue. I can imagine that it will be just easier to
> let u-boot spl end up in while loop instead of trying to find out address for adding breakpoint.
>
In our use case, we do not have physical access to the board.

Previously, u-boot spl would hang when ready for the u-boot image; the
explicit JTAG boot mode keeps from attempting to load images from RAM.

The while(1) loop is, as mentioned by Michal, just an easy, known place to let
the u-boot spl end up before loading images.

Soren will be back in one week and it would be best for him to chime in.

Thanks,
Ezra

> I would let Soren or Ezra to justify this use case because I have doubts.
>
> Thanks,
> Michal



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