Raspberry Pi Pico Bit-Bangs 100 Mbit/S Ethernet
12 comments
·October 29, 2025ggm
this is classic computing wheel of life stuff (Bell, Mudge, MacNamara wrote that up in the 70s)
* first you do it in the cpu * then you do it in a dedicated card off the bus * then you find the FPGA or whatever too slow, so you make the card have it's own CPU * then you wind up recursing over the problem, implementing some logic in a special area of the cpu, to optimise its bus to the other bus to ...
I expect to come back in 10years and find there is a chiplet which took the rpi core, and implements a shrunk version which can be reprogrammed, into the chiplet on the offload card, so we can program terabit network drivers with a general purpose CPU model.
ChuckMcM
Fun stuff. You kids don't know how lucky you are to have really capable MCU's for just a few bucks. :-)
It is kind of the ultimate "not a TOE[1]" example yet.
[1] TOE or TCP Offload Engine was a dedicated peripheral card that implements both the layer 1 (MAC), layer 2 (Ethernet), and layer 3 (IP) functions as a co-processing element to relieve the 'main' CPU the burden of doing all that.
nine_k
Don't modern NICs do a lot of the same, too?
unixfg
Would this have been possible without PIO?
codebje
On a Pico? No - the PIOs replace other peripherals a µC might be able to use to achieve this sort of bitrate, so you'd not really have the tools you'd need to change GPIO pin states once every 3-4 CPU clock cycles.
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.
kfterrg67
>"bit-banging" typically means using the CPU
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.
Neywiny
Ehhhhh the picture shows a very short cable. You can most certainly find micros that can run 100Mb/s communication interfaces, though sure maybe not bitbanged. However, you really need a PHY and magnetics. MII is 25MHz which seems fine. GMII is 125 MHz SDR which is something. Honestly that would've been a cooler demo IMO than running 2 inches
tylerflick
Not at that transfer rate. SPI which is the next fastest (common) protocol you find on micros typically operates around 10 Mhz, but this isn’t an apples to apples comparison.
brcmthrowaway
How does PIO compare to Cypress PSoC?
deckar01
PIO is a set of coprocessors designed to offload signal processing. They have to be programmed. PSoC has FPGA like configuration capabilities, but rather than just logic gates it includes larger analog and digital ICs. You can route analog signal processing in and out without hitting a CPU and perform some FPGA like DSP driven by an arbitrary clock signal.
hackingonempty
PIO is great but the competition has working silicon and SDK for all of the common peripherals while RP gives you crappy example code. Want to connect to an audio codec with I2S? Almost every MCU has this built in but for RP2040/RP2350 you'll have to roll your own production quality version from a demo that only shows how to send. Years after release.
Something related to this that is really cool is directly reading from PDM microphones using PIO: https://github.com/ArmDeveloperEcosystem/microphone-library-.... This shouldn't be called bit-banging though if it's using PIO.