I think that it would be very handy to have the ability to run a Chibi radio directly from my laptop. For example, I'd like to have a "sniffer" when debugging my sensor system.

My first thought was to get a MCU with a USB interface and have it run the Chibi stack, with a very simple application that passes through transmit and receive packets up to the host using the serial over USB protocol. My second thought is that maybe that already exists...

Is there a USB to SPI device out there I could use to talk directly to Chibi from ported drivers running on the laptop? One issue is the interrupt and how that gets communicated across USB to the host.

Hi there,

Maybe the avr-cdc is close to what you want. It provides a wrapper to access an AVR's internal I/O and Timers, etc.

here's the link: http://www.recursion.jp/avrcdc/cdc-io.html#usage

I think Akiba is using the CDC as well to make them virtual serial thru USB to the AVR uC.

Hope this helps,

-Tim

If you want a direct USB to SPI interface, you can try out the bus pirate.
http://hackaday.com/2008/11/19/how-to-the-bus-pirate-universal-serial-interface/

or Travis Goodspeed's GoodFET:
http://goodfet.sourceforge.net/

However as you mentioned, the interrupt won't come through. I would actually use a chip with a USB interface to talk to your boards. If you want a wireless sniffer, you should check out Microchip's ZENA which is a good low cost 802.15.4 sniffer:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en520682

I really need to make an open source 802.15.4 sniffer...*sniff*

Crap, forgot you're using 900 MHz. ZENA won't work since its only 2.4 GHz. There isn't an open source sniffer for that frequency band yet. Guess its up to us, guys!

I've been letting my subconscious work on this problem. Usually, it comes though with something interesting, but apparently not this time.

I see two options:

1) Sniffer on a MCU. Implement the driver down on the MCU, set up Chibi in promiscuous mode to receive everything. Any packet received is sent up USB to the host as ASCII string with time stamp, maybe with a little parsing. Thus, any terminal program on the host will work. Provide for a few commands down, such as changing channel. I'd probably do this on an Arduino board that has USB (but probably not use Arduino bootloader, unless Akiba is about to release an Arduino sku of the driver), so it is easier for others to implement with easily available off the shelf boards. I might make an Arduino shield to connect to the Chibi 20-pin connector, but it would also be possible to hack a ribbon cable connection from Arduino stacking connectors to Chibi 2x10 connector without a shield PCB.

2) Bus Pirate SPI interface to host. This would require writing the sniffer code and Chibi driver up on the host, and constantly querying Chibi to see if there has been a packet received. I believe this is actually significantly harder than #1.

Any thoughts on other ways to go about this?

For a sniffer, you'd pretty much do what you just mentioned in (1). The 802.15.4 chip needs to be in a promiscuous mode with autoACK turned off. From there, its just grabbing the data and sending it to the host PC. The bus pirate is prob not a good way to go.