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@ -10,7 +10,7 @@ CaribouLite is an affordable, educational, open-source SDR platform that is also
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Unlike many other HAT projects, CaribouLite utilizes the <B>SMI</B> (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.
Unlike many other HAT projects, CaribouLite utilizes the <B>SMI</B> (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 [iosoft.blog](https://iosoft.blog/2020/07/16/raspberry-pi-smi/) (code in [git repo](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 [Secondary_Memory_Interface.pdf](docs/smi/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.
In our application, each ADC sample contains 13 bit (I) and 13 bit (Q), that are streamed with a maximal sample rate of 4 MSPS from the AT86RF215 IC. This channel requires 4 bytes (samples padded to 32-bit) per sample (and I/Q pair) => 16 MBytes/sec which are 128 MBits/sec. In addition to the 13 bit for each of I/Q, the Tx/Rx streams of data contain flow control and configuration bits. The modem (AT86RF215) IC by Microchip contains two RX I/Q outputs from its ADCs (one for each physical channel - sub-1GHz and 2.4GHz), and a single TX I/Q intput directed to the DACs.