[Gghc-discuss] Erich's software questions

[Jonathan Manton]

Responses below:

On Apr 25, 2011, at 11:12 AM, Erich Heine wrote:

> Thanks! There are more responses inline below. First tho, can you  
> please put the relevant info in the wiki also? It needs to be there  
> anyway and having a good single, canonical, reference point is  
> always a good thing.
>

Yes, when I get a chance.


> On Mon, Apr 25, 2011 at 10:42 AM, Jonathan Manton <jmanton at illinois.edu 
> > wrote:
> The connection between the User Arduino and the Duinolab Controller  
> is intended to be some sort of serial protocol using the NewSoftSer  
> Arduino library.  I have defined the pins that are used for that (on  
> the pinouts wiki page, for the shields), but have done nothing with  
> software to implement that connection.
>
> Can those pins use the build int UART? Are they buffered? Do we need  
> to use a special library?
>

You *can* use the hardware UART, but then you are sharing it with the  
USB interface, and you will get junk you don't expect going both ways,  
which is probably not a good thing.  Lots of people (on forums, blog  
posts, etc.) recommend against using the hardware UART it if you will  
ever have both USB and your peripheral in use (or even plugged in) at  
the same time.  So you *can* use it if you want, but then you would  
have to physically unplug the connection between the User Arduino and  
Duinolab Controller every time you change and download some code,  
which would probably be kind of a pain.  You would also lose the use  
of the serial console on the PC for debugging.

My recommendation is to try out the NewSoftSerial library described  
here:  http://arduiniana.org/libraries/newsoftserial/

>
>
> So you are now writing the api on top of I2C as well as all the  
> hardware? Instead, why don't you just provide a pointer to the  
> controller documentation, and a list of which pins connect which  
> LEDs/peripherals. The software can be written and debugged by others  
> that way, and take some work load off you.
>

I have to do that work (and indeed, have already done that work) to  
make sure the wiring is correct.  It is already done, and in git  
(testcode/SAA1064test/SAA1064test.pde - despite the name, also has  
code for the I/O expander).

It *would* be nice if someone can take that code and package it into a  
library, and create the appropriate #defines for each of the LEDs/ 
peripherals based on the pinouts in the wiki.

The parts being used are the SAA1064 (LED controller) and PCA9535 (I/ 
O) expander.  The analog switching is done with a 4066B analog switch  
(but that is not an I2C peripheral - it is controlled via pins on the  
PCA9535).  I linked datasheets to those on the resources page.


>
>
> This API will be on the Duinolab Controller.  There still has to be  
> some sort of communications protocol between the User Arduino and  
> Duinolab Controller (I am not implementing that - I think Brian was  
> working on it).
>
> Yeah, there needs to be that, but there are a lot of things to work  
> out aside from that. The end user API is not the same as internal  
> interfaces  to use between components we are in charge of. This is  
> they type of stuff I am talking about.
>

Yep, I haven't done any of that (and don't plan to, at least in the  
timeframe for GGHC).

>
> Can they be put on an interrupt (eg pushing the button changes the  
> state of both the pin representative of the button and the interrupt  
> pin)?  This makes life much, much easier from a software pespective.  
> Doubly so if the non-standard serial pins also don't cause  
> interrupts to be fired.
>

Two of the three buttons could be put on interrupts (pins 2 and 3).   
But there are only 2 external interrupts mapped to pins on the Arduino  
Uno.  So if you want to use more than 2 buttons, you'll have to do  
polling anyway for at least one, and it is probably easier to just  
treat all buttons the same.

You *can* put the polling routine on a timer interrupt.  And I believe  
there are already Arduino libraries out there that do that (e.g., http://arduino.cc/playground/Code/Buttons 
  though there are 4 or 5 different button libraries referenced at http://arduino.cc/playground/Main/InterfacingWithHardware#Input 
  ).