Pixel (Teensy Pixie) SDR

[boxxofrobots]

I've been mucking around plans to produce a Teensy SDR shield of the most basic design. One stumbling block has been finding a clock source. I'm hoping to make use of the SPI clock as a carrier source but am really having a hard time figuring out if this is even practical. Is there anyone here familiar with this or where the documentation exists on how to use SPI port? Does it even provide a stable clock? Would I have to constantly cram null data into a buffer in order to keep the clock running?

 

[gfvalvo]

The SPI hardware is detailed in the appropriate chip datasheet: https://www.pjrc.com/teensy/datasheets.html
I believe at least some of them offer the feature of a continuous clock.

Using an FTM might be a better option.

 

[boxxofrobots]

I looked at the datasheet and downloaded it, and in the part about controlling the SPI clock it says "look in the chip specific document." I thought that WAS the "chip specific document?"

My goal is to make a radio transceiver using nothing more than a T4 and a handful of transistors and a single stereo amplifier chip (to replace the single LM386, used in the original pixie). I'm hoping the SPI or some other pin on chip can generate a clock to at least a few MHz with reasonable tuning resolution.

 

[gfvalvo]

I've only worked directly with SPI hardware on T3.x. On that family of processors I pretty sure the SPI clock setup doesn't offer the resolution you're looking for. That's why I suggested using one of the FTMs.

No experience with the processor on T4.

 

[boxxofrobots]

What I have found is a PLL dedicated to video, which I am hoping to find out is not used by the Teensy audio library. That PLL can be adjusted in 1hz increments from 650 to 1300MHz and then routed to one of the four general purpose timers. From there I just need to find out which pin I can route it to.

It's a lot to learn, this thing has so many registers and configuration bits.

It would be really cool to figure this out, so many people building sdrs with si5351 clock generators when there is so much horsepower on the Teensy 4.x itself.