Re: JTAG debugging of the kernel

[Peter Barada <peterb@logicpd.com>]

On Fri, 2008-08-15 at 14:57 -0400, Josh Karabin wrote:
> Peter Barada wrote:
> > On Fri, 2008-08-15 at 23:04 +0530, Syed Mohammed, Khasim wrote:
> >>> -----Original Message-----
> >>> From: linux-omap-owner@vger.kernel.org [mailto:linux-omap-owner@vger.kernel.org] On Behalf Of Peter
> >>> Barada
> 
> >>> Any suggestions on what can cause the JTAG to stop working after the
> >>> kernel starts?
> >>>
> >> I think you should disable Power Management. Which kernel are you using now?
> > 
> > 2.6.22.18.  I'm planning to move to 2.6.26 after the dust settles...
> > 
> > I'll try w/o power management, but any idea why power management might
> > affect JTAG?
> 
> The guy I share an office with (who's out on vacation) worked through 
> this with their tech support, who suggested replacing WFI instructions 
> with NOPs.
> 
> Look at cpu_v7_do_idle in arch/arm/mm/proc-v7.S.  Changing the WFI to a 
> NOP did the trick for him.
> 
> Presumably power management was off, but even WFI (wait for interrupt) 
> put the CPU in a state that wasn't handled by the BDI firmware at the 
> time.  I'm not sure if they resolved the issue in a later firmware 
> update or not.  We didn't think the workaround was worthy of a Kconfig 
> option - hopefully updated firmware for the BDI box will address the issue.

Hmm, trying both disabling power management and changing the WFI to NOP
in cpu_v7_do_idle does not work, the BDI times out when I try to halt
the processor.  I'm running with version 1.07 of the BDI firmware.  Is
this what other people are successfully using to debug the kernel with a
BDI-2000?

> 
> - Josh