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Why does the CubeSat Kit use SD Memory?

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Why does the CubeSat Kit use SD Memory?

Postby Unregistered User » Fri Aug 26, 2005 8:03 am

Can you do me a favor please?

Can you ask to your team why to use an SD Memory instead of I2C EEPROM?

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Re: Why does the CubeSat Kit use SD Memory?

Postby aek » Fri Aug 26, 2005 8:03 am

We chose the SD interface for the CubeSat Kit several reasons:

1) It's a standard package, available everywhere, in capacities from 32MB on up. As long as there are SD cards you will be able to add memory to your CubeSat Kit.

2) By being removable, you can exchange data between your PC and your CubeSat Kit while in the development stage. E.g. you can put pictures on the SD card via a PC, and then test your CubeSat Kit code against the pictures on the SD card.

3) SPI is generally much faster than I2C. Much easier to interface, also.

4) There was plenty of room on the underside of the FM430 PCB for the SD card socket.

So, here is the suggested peripheral usage of the CubeSat Kit:

USART0: USART (for user stuff, e.g. cameras or other things with serial interfaces) OR I2C (for peripherals) OR SPI (for SD card or peripherals).

USART1: USART (for transceiver) OR USART (for USB) OR USART (for user stuff, e.g. cameras) OR SPI (for peripherals)

Note that each USART can do multiple things. For Example, KatySat will use USART0 to interface to a camera, the SD card and I2C stuff. Access will be managed via the Salvo RTOS via resource locking.

The downsides of the SD card include a socket that may or may not be good enough for the vibration, and that SD cards have a narrower temperature range (-25C to +65C) than the rest of the FM430 Flight Module (-40C to +85C). We hope and suspect that neither of these will be a big issue.

Lastly, it's important to remember that since peripherals like the SD card interface are directly on the FM430 Flight Module's MSP430's bus, you can develop your own system in place of ours. E.g. if you like the SD card idea but are worried about the connector, then implement your own SPI-based memory solution on a user module (connected via the CubeSat Kit bus), and simply leave the FM430's SD card out. Or leave the SD card out and do your own memory solution (again on a user module) via I2C.

The code we're suggesting that people use for SD is for example here: http://www.egr.msu.edu/classes/ece480/goodman/fall/group05/work/index.html We used this (slightly altered for a lower speed SPI connection) to test all of the CubeSat Kit Test Board B's.

The next revision (Rev C) of the FM430 will have a properly functional SD card slot on it. We will have an exchange program for anyone with a Rev B FM430 Flight Module. Owners of Rev A FM430 Flight Modules will have the opportunity to upgrade to the Rev C FM430 Flight Module at a discount.


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