Hi Thierry, On 25.05.2012 19:40, Thierry Reding wrote: > * Stephen Warren wrote: >> On 05/25/2012 07:46 AM, Thierry Reding wrote: >> > The PI4 GPIO is used on Tamonten to reset carrier board peripherals. >> > Power sequencing hardware on the carrier pulls the reset low before >> > powering up the Tegra, and the CPU is supposed to signal readiness, >> > and therefore bring peripherals out of reset by pulling PI4 high. >> >> > +void gpio_early_init(void) >> > +{ >> > + gpio_request(GPIO_PI4, NULL); >> > + gpio_direction_output(GPIO_PI4, 1); >> > + gpio_free(GPIO_PI4); >> > +} >> >> Do you really mean to free the GPIO here? >> >> While gpio_free() does not do this at present, it seems perfectly >> reasonable for someone to modify gpio_free() so that instead of leaving >> the HW in some random state when free, it actively reprograms the pin to >> be an input instead, since that's the most conflict-free setting when >> the pin is actively unused. > > I believe that even a pulse would be enough for the undelying mechanisms to > take effect, but I'll have to check with our hardware engineers to be sure.
As an aside: A pulse wont be enough in this specific case as a pull-down on the carrier would lead to the nRST going low thus resetting the baseboard peripherals. Plus there is a status LED on the Tamonten Evaluation carrier that would then indicate the red "system not up". Cheers, Kai _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot