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    Unlike many other HAT projects, CaribouLite utilizes the SMI (Secondary Memory Interface) present on all the 40-pin RPI versions. This interface is not thoroughly documented by both Raspberry-Pi documentation and Broadcomm’s reference manuals. An amazing work done by https://iosoft.blog/2020/07/16/raspberry-pi-smi/ (code in https://github.com/jbentham/rpi) in hacking this interface contributes to CaribouLite’s technical feasibility. A deeper overview of the interface is provided by G.J. Van Loo, 2017 https://github.com/cariboulabs/cariboulite/blob/main/docs/Secondary%20Memory%20Interface.pdf. The SMI interface allows exchanging up to ~500Mbit/s between the RPI and the HAT, and yet, the results vary between the different versions of RPI. The results further depend on the specific RPI version’s DMA speeds.

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      Whoa that is news!

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      Neat that they’re able to use an 802.15.4 smart meter transceiver’s raw I/Q mode feature for this. That chip is US$2.50 qty 1 on Digikey, a fraction of the cost of the same parts in a “normal” SDR. And compared to the low cost R820T tuner in rtlsdr, it can transmit as well!

      It’ll be interesting to see what the performance across the whole 30Mhz-6Ghz frequency range is, given the advertised frequencies for the chip are only 390-2480MHz. Still, even that’s a big range by itself.

      The only other thing I can see to quibble over is that 4MSPS sample rate will limit its use for some applications, even the R820T is good for 8-9MHz usable bandwidth.

      It still looks awesome, especially if it’s cheap - and it looks like it will be very cheap for an SDR!

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        They’re using a Lattice ICE40 with the yosys+nextpnr open source FPGA toolchain as well, nice!