AVR Butterfly and external storage (repost)

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(sorry, I posted this in the wrong forum previously - perhaps a moderator can remove earlier version)

Just to confirm - is there a preferred way to use external storage with the AVR Butterfly? 512k flash is not enough, but otherwise the device meets my requirements.

Having searched the internet and these forums, it seems that the best approach is to use the 4 JTAG pins with an MMC card - both of these being documented techniques.

I would prefer to use CF (because I have some stock) - is there an IC that can allow me to interface serially to the CF ? (otherwise, there don't seem to enough pins on the AVR Butterfly left for native access).

I don't plan to use a file system: I will be writing to the blocks directly, and then later extracting the raw blocks under BSD.

Thanks for any feedback.

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Since the number of free pins is limited on the BF MMC might be the better choice. Maybe the controller could be connected to some of the MMC-pads thru the hardware-SPI pins available at the ISP connector.

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It seems that I can use the 4 free JTAG pins (PORTF 4,5,6,7) or the 3 free USI pins (PORTE 4,5,6); as MMC requires at least 4 lines (DIN, DOUT, CLK and CS).

Using the 4 JTAG pins would require bit-bang software SPI. On the other hand, the datasheet suggests that USI can act as an SPI master, thus giving me hardware SPI using DIN/DOUT/CLK on 3 USI pins, and CS on one of the JTAG pins. That still leaves 3 JTAG pins free.

Can anyone confirm that they've used Butterfly or mega169 USI in SPI master mode? I've read the datasheet, but would be interested in confirmation that there are no caveats.

Thanks