zlacker

>>evakho+(OP)
> I like the Raspberry Pi RP2040 a lot. It's relatively cheap (around $1 USD) and has tons of on-board RAM - 264 KB in fact! It also has what is called Programmable IO, or PIO.

I wonder how benchmarks would compare between the RP2040 and, say, a Z80.

>>zahlma+4h
The RP2040 is a Cortex-M0, which is about the smallest core you find on modern systems but still a pipelined 32 bit RISC machine running in the dozens of MHz.

Note though, that the article is really about the PIO device on these SOCs', which isn't part of the main CPU at all. It's sort of a very limited programmable hardware engine for the specific task of doing PCB level interconnect using GPIO and lightly buffered streaming. In some sense it's like a thematic midpoint between an FPGA and a CPU.

It's... honestly it's just really weird. And IMHO has really, really, REALLY limited application. It's for people who would otherwise be tempted to bitbang an I2C or UART, but not for ones who can put hardware on the board themselves, or who have a FPGA handy, or even for people who want to do non-trivial stuff like QSPI displays[1] or whatnot.

Basically PIO smells like a wart to me. I genuinely don't know who wants it. Regular hackers aren't sophisticated enough to use it productively and the snobby nerds have better options.

[1] The linked article appears to be doing a quarter-VGA display in 3-bit/8-color, and is sort of right at the limit of the power of the engine.

>>ajross+Aw
> The linked article appears to be doing a quarter-VGA display in 3-bit/8-color, and is sort of right at the limit of the power of the engine.

The resolution and color depth restrictions were the product of the low data rate of USB FS (~12 Mbps), not inherent limitations of PIO.

> It's... honestly it's just really weird. And IMHO has really, really, REALLY limited application.

I'd agree with "weird". But it's useful weird; it turns out that there are a lot of situations where PIO can avoid the need for an application-specific peripheral, and can provide that function in a more flexible fashion than a fixed-function peripheral could. Dmitry's SDIO device emulator is a great example - almost every other SDIO peripheral on the market is host-only.

>>duskwu+sL
> it turns out that there are a lot of situations where PIO can avoid the need for an application-specific peripheral

And I can only repeat: I think that's an aspirational delusion. I'm not aware of anyone shipping a PIO solution to anyone in volume. It's "useful weird" to Hackerspace nerds like us, and that leads to some epistemological skew.

Hardware needs to be boring and reliably supported (by people you can sue!) or else no one will bet a 10k unit PCB run on it. This is anything but.