Raspberry Pi Hat Adds SDR With High Speed Memory Access

The Raspberry Pi SDR add-on is not a new idea, but an open source one The cariboulite project looks like a great entry into the field. Even if you are not interested in radio, you may find the use of a special high-bandwidth memory interface for Pi interesting.

The interface in question is the poorly documented SMI or Secondary Memory Interface. [Caribou Labs] helpfully provides links to others who did the work to understand the interface together with code and a White paper. The result? Depending on the Pi, the SDR can exchange data of up to 500 Mbps with the processor. The SDR actually uses less than that, with about 128 Mbps. However, it would be difficult to transmit so much data by conventional means.

On the radio side, the SDR covers 389.5 to 510 MHz and 779 to 1,020 MHz. There is also a wide tuning channel from 30 MHz to 6 GHz, with some exceptions. The board can transmit at about 14 dBm, depending on the frequency and the value of the received noise is below 4.5 dB for the lower frequency bands and less than 8 dB above 3,500 MHz. Of course, some Pis already have radio, but not with this kind of opportunity. We have also seen the SMI drive many LEDs.