[TangerineSDR] A few thoughts after Monday night telecon

[Franco VENTURI]

First of all, thanks for the very interesting telecon last Monday night; I apologize I had to drop at around 10:30pm, but it was getting late here.
 
With this message to the list I want to try to put on 'paper' some of the points of Monday discussion (plus a few other things I found out after that) to help moving forward. Please feel free to comment and add your thoughts (and correct my errors and omissions, of course).
 
- the basic plan would be to have the ADC (AD9648) in the Tangerine SDR RF board somehow send the 'raw' stream of samples to the computer at 'full' speed; all the DSP processing would occur in the computer; a good approach for this would be Phil Karn's KA9Q ka9q-radio program running on the computer (fast convolution filter bank)
- by 'full' speed we mean dual 16bit streams at 122.88MHz; the 16bit number comes from 14 bit from the ADC + 1bit for overflow + 1 bit to mark the PPS sample (if I understand correctly how Tom does it); doing some quick math this means being able to transfer to the computer about 3.932Gb/s
- the USB 3.0 controller used by the RX888, Cypress/Infineon FX3, is capable of streaming about 32bit @100MHz, i.e. 3.2Gb/s
- to reach the transfer rate of almost 4Gb/s there are two approaches: scale horizontally (i.e. two FX3 controllers) as suggested by Rob Robinett, or scale vertically (USB 3.1 gen 2, USB 3.2 gen 2, or USB 4); these can offer another USB mode called SuperSpeed Plus with a signaling rate of 10GHz, i.e. probably capable of transfer rates of the order of 8Gb/s. These last couple of days I searched on the Internet, and I couldn't find a 10Gbps USB peripheral controller that could be used in a way similar to the FX3. Monday night I thought Cypress/Infineon CCG6SF and CCG6DF could do it, but looking at this document (https://new-origin.infineon.com/dgdl/Infineon-EZ-PD_CCG6DF_CCG6SF_USB_Type-C_Port_Controller-DataSheet-v11_00-EN.pdf?fileId=8ac78c8c7d0d8da4017d0ee8e2c571be), there is no mention of 10Gbps
- someone mentioned that it wouldn't be too hard to modify the design of the data engine board to use one or two FX3's instead of the FPGA, and I would be very interested to understand better this option
- also I think that someone mentioned that the FPGA could still be used to do some preprocessing of the data and reduce the amount of data that would need to be transferred via the USB 3 connection; perhaps sending the sum and the difference of the two streams could reduce the bandwidth required, since the difference would probably require less bits to be sent, similar to how the FM stereo signal is broadcast
- another option to achieve that kind of transfer rate would be via PCIe, but in this case I think the data engine board would have to be a PCIe board, and that might make the design more complicated, not sure.
 
I think this is all; I just wanted to start a conversation and I am looking forward to hearing your ideas.
 
73,
Franco Venturi K4VZ
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