David Kuehling wrote: > will the Uart be usable with (non-inverted) TTL level interfaces, as > present as debug port in many embedded designs (including the > wikireader)?
The current design operates at 3.3 V, like the rest of the Ben. It should be able to drive most 5 V inputs. A 5 V output connected to the UART board would inject a current of about 10-15 mA, which is probably low enough not to cause trouble. (You could reduce this by increasing R1.) > SW flow control can be used instead. Best would be if the corresponding > code was part of the uart board firmware (and not part of the more > latentcy-suffering linux driver). Hmm, maybe. In some cases, it may be desirable to be able to switch flow control off entirely, in which case this would increase the complexity of communication, because the TTY layer (i.e., the scary part of Unix serial communication) would have to communicate the change of flow control through the low-level driver. > Not that I demand that _you_ coded up a driver :) I guess a > script-language (python/lua/forth?) test software would be sufficient to > verify the spi interface works. I would do the proof-of-concept user space just in C. It's easy to control the port pins. Scripting languages sometimes have problems with such low-level things, and C also allows you to drive things at the maximum speed the CPU is capable of, so you can find timing issues you'd also have in the kernel. Here are some examples, in increasing degree of complexity: http://projects.qi-hardware.com/index.php/p/ben-blinkenlights/source/tree/master/bbl/bbl.c http://projects.qi-hardware.com/index.php/p/f32xbase/source/tree/master/f32x/gpio-xburst.h http://projects.qi-hardware.com/index.php/p/f32xbase/source/tree/master/f32x/gpio-xburst.c http://projects.qi-hardware.com/index.php/p/ben-wpan/source/tree/master/tools/lib/atben.c Important: before you try to take control of the 8:10 card, you need to ask the kernel's MMC driver to step aside: echo jz4740-mmc.0 >/sys/bus/platform/drivers/jz4740-mmc/unbind I have an unfinished project that aims to provide some assistance with obtaining/relinquishing access to the GPIOs: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/libbb (Back when I did this, there was a kernel problem that prevented it from working. This has been solved by now, but I haven't tried so far to see if things work now and what else is needed. One item on my post-wpan to do list :-) - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
