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Re: [Paparazzi-devel] using SPI slave on Tiny2.11


From: Bart Remes
Subject: Re: [Paparazzi-devel] using SPI slave on Tiny2.11
Date: Wed, 3 Nov 2010 17:56:37 +0100

Hey,
Veryinteresting!!
when you get things working can you add them on the wikky?
A basic example on the wikky on your setup will be nice.
I`m sure a lot ofpeopleareinterestedin a tiny and a gumstix.
The morepeopleinvolved the sooner problems are solved.

keep up the good work!!
Bart


2010/11/3 Jlus Helgi Bjarnason <address@hidden>
Hi Adam,

It's nice to see someone working at similar thing as me.

I haven't started any work on the code for the tiny because I am still making myself familiar with the current paparazzi code. I have an funjet airplane and and we have used tiny as autopilot and it worked fine. Now we are adding the gumstix to the airplane. The gumstix is ready and the next step is to modify the code for tiny to make them communicate. I am working on this as my final project for my BSc degree in electrical engineering and am working on this almost 24/7. If we can work on the code together we can hopefully get more work done quicker.

I came across the errata document for the LPC processor that explains problems when the CPHA is 0. I'm not sure if that is relevant but the file is at http://www.nxp.com/acrobat_download2/erratasheets/2148.pdf

Jlus
________________________________________
Fr: paparazzi-devel-bounces+julius07=ru.is@nongnu.org [paparazzi-devel-bounces+julius07=ru.is@nongnu.org] Fyrir h&#246;nd Adam Spence [address@hidden]
Sent: 2. nvember 2010 23:45
Vitakandi: address@hidden
Efni: Re: [Paparazzi-devel] using SPI slave on Tiny2.11

Hey Jlus,

I've been working with the SPI slave on a tiny 2.11 in the last couple of weeks. I wasn't having a lot of success using the entire build and had to start from scratch to work out a few issues.

I am now in the posistion which I can effectively communciate using the SPI slave but there are a few issues. So far I have been unsuccessful in getting the CS to work properly when the phase (CPHA) is set to 0. For whatever reason I cannot get an external master to communicate. I'm using an AVR as the master and between two AVRs, the code works fine. As a result I'm having to always ensure that CPHA is set to 1. This effectively ignores the CS and has to be held low. This may not help you! If you find out what's wrong I would love to know. I've monitored the CS line on a scope and it's behaving as expected but the Tiny does not generate an interrupt.

On another note, the existing slave code appears to disable the receiver after every byte. I could not find a slave usage example so ended up commenting this out to get it to work.

Finally, as we're using CPHA = 1 there can be an issue with the slave/master getting out of sync by a number of bits. So far I the only way I have found to fix this is to disable and then re-enable the SPI in the SPI rx interrupt. This is not an ideal solution and there is currently no understanding as to why this worked. As it solved my problem I will probably proceed for now and when I get time go back and investigate.

The external AVR is currently using a UART to communicate with a Spektrum reciever and then pass this on to the Tiny, I have other pressure sensors that this will eventually end up driving but for now it's a simple UART to SPI bridge.

I would love to know if you get further than I did. I only have a few hours a week to work on this so it may take me a while to figure out entirely.

Hope this helps!

Adam

2010/11/2 Jlus Helgi Bjarnason <address@hidden<mailto:address@hidden>>
Hi all,

I'm trying to use SPI to let Tiny2.11 and Gumstix talk to each other. The mission is to have Gumstix as SPI master and gather some data from some devices such as humidy sensors, heat- and pressure sensors. The gumstix will also do other things like controlling a GSM/GPRS modem to send the data to a data store. I want the tiny2 to be the autopilot and use SPI for communication with Gumstix. This means that it has to be an SPI slave since the Gumstix is the master. The problem is that all the modules in paparazzi are using the SPI as a master. There are some definitions for an SPI slave in the hardware code for SPI but I don't see any other code using that. It would be good to know if anybody else is working on a similiar project. Is anybody else using the Tiny2 as an SPI slave?

Jlus Helgi Bjarnason
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