Would this have been possible without PIO?
replies(2):
In a sense the PIO is a bit 'cheaty' when claiming "bit-banging", because the PIO is the ultimate peripheral, programmable to be whatever you need. It's no mean feat to make the PIO do the sorts of things happening here, by any stretch, but "bit-banging" typically means using the CPU to work around the lack of a particular peripheral.
From that perspective, there's precious few µCs out there that could bit-bang 100MBit/s Ethernet - I'm no expert, but I _think_ that's a 125MHz IO clock, so if you want 4 CPU cycles per transition to load data and push it onto pins, you're looking for a 500MHz µC, and at those speeds you definitely have to worry about the bus characteristics, stalls, caching, and all those fun bits; it's not your old 8-bit CPU bit-banging a slow serial protocol over the parallel port any more.
This is significant. It's using a hardware peripheral that is designed and intended for high frequency IO manipulation without CPU intervention. This isn't bit-banging, lest we start calling it "bit-banging" any time an FPGA or ASIC or even a microcontroller peripheral handles any kind of signalling.
Here, it runs software that allows it to talk 100mbps Ethernet.
Someone else might use that same hardware peripheral to drive a display, or produce a PWM output, or whatever.
The RP PIOs just run software. That software can bang bits.
And the CPU that's actually deciding on the bits doesn't have to bang them with precise timing, it just has to put them into that buffer.
but Yes on pico2 because RP2350 has separate fast serializer (HSTX) hardware block able to clock out at 2x the global clock (DDR). 320MHz OC results in 600Mbit output. Here example pumping out 175 MByte/s of data encoded as HDMI signal (3 lanes) without touching PIOs https://github.com/steve-m/hsdaoh-rp2350 to be used with $6 MS2130 USB 3.0 4k HDMI Video Capture dongle.