[Tinyos-help] SPI Bus arbitration on micaz

[Philip Levis]

On Aug 3, 2008, at 11:05 PM, Varun Jain wrote:

> Hello Dr.Phil,
> I was looking through the archives and I found that you have  
> discussed the topic about using multiple SPI devices. In the  
> following link you said that you might post some code for using  
> multiple SPI devices:
>
> http://mail.millennium.berkeley.edu/pipermail/tinyos-help/2008-April/032819.html
>
>
> Have you posted it somewhere?? I am trying to attach an LED screen  
> to the SPI interface of the atmel atmega128 processor. My platform  
> (Chipcons CC2420DBK) is very similar to Micaz and I have ported my  
> platform in TinyOS correctly and all the test applications are  
> working correctly. I am now building an application where I need to  
> display certain data to all the nodes in the network and collect  
> data to a BaseStation. So, for displaying I need to attach this  
> external LED/LCD screen.
>
> DOES anyone else has used SPI in micaz to interface some external  
> devices using arbitration. Will the following process work for this  
> task:
>                 Toggle clock line
>                 Set the output line
>                 Send the data from master to slave
>
> Also I wanted to know that if we are using Dissemination to insert  
> data into the network every few seconds, then will it be alright to  
> use SPI to interface external devices as there might be a conflict  
> in accessing the SPI bus.

The micaz does not export the SPI interface via the 51-pin connector:  
it is dedicated to the CC2420. The SPI to the at45db is just bit- 
banged GPIO. You therefore need to connect directly to the atm128 if  
you want to use the SPI. Take a look at the schematic.

For software arbitration, look at platform/micaz/chips/cc2420/ 
HplCC2420SpiC.nc. You'll see that it connects HplCC2420SpiP's to  
Atm128SpiC; the latter provides the power lock to the former. So  
that's Atm128SpiC is the component you want to connect to.

Phil