The flipside of this is that the RP2xxx has rather poor hard IP, and the PIO is not quite powerful enough to make up for it.
They are great for basic hobbyist projects, but they just can't compare to something like an STM32 for more complicated applications.
They are a pleasure to work with and I think that they are great MCUs, but every time I try to use them for nontrivial applications I end up being disappointed.
To give a very basic example: its times can't do input capture. This means you have no easy way to do high-accuracy pulse time measurement. Compare the two datasheets, and the STM33's timers literally have orders of magnitude more features.
Only having two UARTs can be limiting - and PIO is a no-go if you want offloaded parity checking and flow control. The PIO doesn't have an easy external clock input. No CAN or Ethernet makes usage in larger systems tricky. There's no USB Type-C comms support. Its ADC is anemic (only 4 channels, with 36 io pins?). There are no analog comparators. It doesn't have capacitive touch sensing. There's no EEPROM.
None of them are direct dealbreakers and you can work around most of them using external hardware - but why would you want to do so if you could also grab a MCU which has it fully integrated already?
That is exactly the problem: you need to use PIO to constantly read the pins, and analyze the bitstream in software. At high speeds this takes up a substantial fraction of your compute resources, and it makes any kind of sleep impossible.
On a STM32 you can just set up the timer and forget about it until you get a "hey, we saw a pulse at cycle 1234" interrupt. The two are not the same.
My argument wasn't "this is completely impossible", but "this is needlessly complicated".
Agreed; RP2040 doesn’t have true timer input-capture like STM32 (no CNT->CCR latch on edge). That criticism is fair.
What Pico/RP2040 projects do instead is use a PIO state machine clocked from the system clock to deterministically timestamp edges (often DMA’d out). It avoids ISR latency and gives cycle-accurate edge timing relative to the MCU clock. It’s not a built-in capture peripheral, but it achieves the same practical result.
If you want a drop-in hardware capture block with filtering and prescalers, STM32 is the better choice. RP2040 trades fixed peripherals for a programmable timing fabric.
Can you give an example of a chip with software-defined IO coprocessors that is 1/4 the price? The pricing I’m getting on the RP2350 is 0.6EUR per chip.
When I’ve compared to other dual-core SoCs with programmable IO, like NXP with FlexIO (~€11) or ESP32 chips with RMT (~€1) they are much more expensive than the RP2350.. is there a selection of programmable IO chips I’m missing?
That's the thing: with proper dedicated peripherals you don't need the software-defined coprocessors.
Sure, they are great if you want to implement some obscure-yet-simple protocol, but in practice everyone is using the same handful of protocols everywhere.
Considering its limitations, betting on the PIO for crucial functionality is a huge risk for a company. If Raspberry Pi doesn't provide a well-tested library implementing the protocol I want (and I don't think they do this yet), I wouldn't want to bet on it.
I think they are an absolutely amazing concept in theory, but in practice it is mostly a disappointment for anything other than high-speed data output.
In Cortex M33 land $15 will get you an entire NXP (or STM) dev board. An MCX-A156 will set you back about $5 which is about on par with an STM32H5. You can go cheaper than that in the MCX-A lineup if you need to. For what I'm working on the H5 is more than enough so I've not dug too deep into what NXP's FlexIO gives you in comparison. Plus STM's documentation is far more accessible than NXP's.
Now the old SAM3 chip in the Arudino Due is a different beast. Atmel restarted production and priced it at $9/ea. For 9k. Ouch. You can get knockoff Dues on Aliexpress for $10.
Edit: I'm only looking at single core MCUs here. The MCX-A and H5 lineups are single-core Cortex M33 MCUs. The SAM3 is a single core Cortex M3. The RP units are dual core M33. If the RP peripherals meet your needs I agree that's a great value (I'm seeing pricing of $1+ here).
Edit2: For dual core NXP is showing the i.MX RT700 at around $7.
That's true in general, but people do use these hobbyist boards as an alternative to a manufacturer dev board when prototyping an actual product.
It's reasonably common in the home automation space. A fair few low volume (but still commercial nevertheless) products are built around ESP32 chips now because they started with ESPHome or NodeMCU. The biggest energy provider in the UK (Octopus) even have a smart meter interface built on the ESP32.
They are great for basic hobbyist projects, but they just can't compare to something like an STM32 for more complicated applications.
They are a pleasure to work with and I think that they are great MCUs, but every time I try to use them for nontrivial applications I end up being disappointed.