AT91: Fix power-saving in idle-mode on 926T processors

[Anders Larsen]

Hej Peter,

On 2011-01-10 16:05:36, Peter Korsgaard wrote:
> On Thu, Oct 7, 2010 at 9:44 PM, Anders Larsen <al at alarsen.net> wrote:
> > According to Atmel, their 926T processors (AT91 post RM9200) requires
> > 'Wait for Interrupt' mode be entered right after disabling the processor clock
> > in order to minimise current consumption when idle, so do both provided we're
> > not running on a 920T (an RM9200).
> 
> Is there a known interaction with this and the JTAG controller?

indeed there is - disabling the processor clock blocks JTAG debugging.

> I haven't had time to look closer into it yet, but with this applied
> I can no longer access an Altera FPGA on a chain shared with a 9G45
> through Quartus.

If you boot with the kernel parameter "nohlt", arch_idle() is not called,
and JTAG should work again (but of course power consumption will be
substantially higher).

This was noted by Uwe Kleine-König in https://lkml.org/lkml/2010/5/5/342

Cheers
Anders