Looking for a MicroController Recommedation

MicroSD connector. Yes, I was looking at this and I have to say it does look promising. I then realised that I already have a Raspberry Pi, so I had a quick go at some bare metal programming on it, but the sampling rate I got on the GPIO pins was woeful. I wrote a program just to turn one of the GPIO pins on and off as fast as possible, but only seemed to get a pulse period of 6ms, which is 5 or 6 orders of magnitude too slow. At that rate even if I use a shift register externally it would be way too slow. I could have been doing something wrong, has anyone else ever tried this? I wonder if bare metal access to GPIO on the beaglebone would be any better than the Raspberry Pi? I have had a quick look at the docs and I can't find anything about the speed of GPIO. I found one post which suggests you can achieve 1.5MHz (http://www.supermicros.org/1/post/2013/07/beaglebone-gpio-musings.html). If that is right then a shift register would be needed, but wider than 8 bits I think. The beaglebone SPI support looks like it might be an alternative. Although I am not clear how fast this can go and whether I could get the timing to be accurate enough. I would need to build some custom hardware that sends data to/from the SPI interface on the beaglebone. That might not be too bad, but I don't really know what is involved at the moment, probably an FPGA to make prototyping easy. run for SD barebox I have not written a driver before, that is a possibility but I feel that bare metal is probably the way to go. > If you want a FPGA consider the ZedBoard. It is much more expensive > (starting at 199 US$) but will give you a dual core Cortex-A9 and a FPGA on That is too expensive :-( Regards Rob