[ECOS] PPC852T port pin configuration questions

Steve Strublic SStrublic@Hypercom.com
Fri Sep 17 17:08:00 GMT 2004

Hi Gary,

Thanks for making the update.  It was a little perplexing.

This code snippet came from eCos 2.0.9.


On Thu, 2004-09-16 at 16:59, Steve Strublic wrote:
> Hi,
> I was investigating an issue with our product, that is using eCos and the PowerPC 852T.  I traced
> down to a specific area of code that configures ports A, B, and C.
> The specific code is in hal/powerpc/mpx8xx/.../src/var_misc.c, and is specific to the 852T.
> #if defined(CYGHWR_HAL_POWERPC_MPC8XX_852T) && !defined(CYG_HAL_STARTUP_RAM)
>     // Only do this if we are not a RAM startup, otherwise we risk
>     // disturbing settings made by RedBoot.
>     // Special settings - according to manual errata
>     eppc->pio_papar &= ~0xffffffff;   // PA manatory settings
>     eppc->pio_padir |=  0xffffffff;
>     eppc->pip_pbpar &= ~0x0003ff07;   // PB29..31 AS GPIO
>     eppc->pip_pbdir |=  0x0003ff07;
>     eppc->pip_pbdat  =  0x00010007;
>     eppc->pio_pcpar &= ~0xffffffff;   // PC manatory settings
>     eppc->pio_pcdir |=  0xffffffff;
> #endif
> Our specific issue is that these are interrupt-capable inputs in our product, and the hardware
> the pins to that state.  Forcing the pins as outputs without completely configuring the PCSO
> register causes the pins to reach a state that is neither zero or one.
> I looked through the errata for the 866/852T and I don't see the need to perform this operation.
> saw no specific errata that stated the values of ports A/B/C/D were unknown at startup.
> In fact, the configuration of port C as all outputs is a specific danger, as they default to
> at powerup.  Driving them as outputs may prevent them from being configured as spurious interrupt
> sources, but in truth the PPC defaults them as general-purpose inputs with no interrupt
> And I don't understand the desire to force ports A and B to their configurations above... I could
> not locate any references in any errata or manual.
> Also, not everyone uses Redboot to boot their product... we aren't.  This causes a difficulty when
> powering up a RAM-based image that does not use Redboot.
> I appreciate any assistance in explaining the desire and logic behind the decisions which required
> this implementation, and any offers of assistance to resolve the situation.

I don't recall right off why I did this, but it seems clear now that
it should go in platform code, not the variant code.  I'll move it
to the only public 852T (the A&M Adder)

That said, the current CVS doesn't match what you've quoted above.
What codebase are you working from?

Gary Thomas <gary@mlbassoc.com>
MLB Associates

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