Comments inline... On 2/25/2011 2:23 PM, Albert ARIBAUD wrote: > Le 25/02/2011 22:44, Bob Feretich a écrit : >> For the BeagleBoard, the pins of interest are the ones routed to the >> Expansion, J4, and J5 connectors. I am working with a local university. >> Students are building projects that interface to these connectors. >> Usually, the Linux boot delay is not a concern, but depending on the >> project, sometimes the pins need to be initialized before a "set time >> interval after power-on" expires (We can set the power-on reset delay to >> several hundreds milliseconds, but the time must be bounded.) > Can you not simply set this time high enough that the U-Boot script > executes? Yes, that would be ideal. But how can I set set pin mux controls, initialize output pin state, and set the pin direction from an automatically executed u-boot script?
>> By having the spot (beagle.c& beagle.h) in u-boot, where we can add our >> I/O Pin Mux initialization code, we can satisfy the needs of a bounded >> I/O initialization time. > Out of sheer curiosity (I've done some lab teaching in assembly language > and device control in a previous life), what are those IOs that have > such a bounded set-up time relative to power-on in a university project? > If you are willing to answer but find that's really not related to > U-Boot, we can discuss this in private. > In the past we have had problems using the McSPI 3 and 4 interfaces on the BeagleBoard Expansion connector. The GPIO pins initialize as 0s which activate the SPI chip selects and the SCLKs (for SPI CPOL=1 devices). Later, when the pin mux is set to select the SPI controller, the SCLK assumes its inactive state (logic 1). Now the SPI devices have observed a 0 to 1 transition of the SCLK and are one bit out of sync with the controller. Activation of a power-good signal can be delayed for a fixed time to prevent the devices from interpreting the SPI bus until it has properly initialized, but the delay should be kept to less than a second. Regards, Bob Feretich >> Regards, >> Bob Feretich > Amicalement, _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
