Saturday, August 20, 2011

The WiFi Trek Begins

I started looking into implementing WiFi in the platform with the Microchip resources and thought that it might be useful to chronicle what I did. This serves the dual purpose of showing others how I go about figuring something out that I've never done before and the resulting blog post can serve as somewhat of a reference note that I can refer back to. So the goal is to send some data over WiFi with the platform. I've never done that before so here's how I'm going about it.

Hardware or Firmware First

I need to create a breakout board for the wifi module but before I do that I want to see how difficult it will be to integrate the Microchip stack into my firmware. If it turns out to be a huge pain then maybe I'll reconsider modules.

Get the Stack

Can't get the stack by itself. You have to download the entire 184MB of the Microchip Application Library and then, on install, you can decide only to install the tcp stack which appears to be a simple file extraction from the massive exe. Oh well, Microchip's business is creating chips not customer friendly software. While that was downloading I decided to give the MRF24WB0MA datasheet a read. More on that in a minute. Once I was done with that the download was finished so I started the download of the library documentation which is another 45MB. Why isn't that in the massive application library exe I just downloaded? Nevermind. While that was downloading I installed Eagle on my Ubuntu machine because I'll need that when I want to create a breakout board.

Datasheet Notes

A few things of interest in the datasheet. Page 11 has the footprint I'll need to create a breakout board in Eagle. Page 13 has an example application schematic that I'll mimic pretty closely in connecting it to the 27J53. Hibernate state can significantly extend battery life but isn't useful for intervals less than 30 seconds. The slave SPI interface implements the [CPOL=0;CPHA=0] and [CPOL=1; CPHA=1] modes (0 and 3) of operation. That is, data is clocked in on the first rising edge of the clock after Chip Select (CS) is asserted. This will be important when setting up the SPI driver in the wifi module. The SPI clock frequency can be up to 25MHz which is fine since currently the platform is running at 16MHz.

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