[InvaderFizz]

I would guess it is to:

1. Build out a RISC-V ecosystem for almost zero cost. The value-add is quite large for a segment of potential buyers as they get the same excellent ecosystem, but can target RISC-V as the uArch.

2. De-risk dealing with ARM in the future as their moves in licensing changes foretell a bleak future for licensees

3. Eventually a bargaining chip with ARM on licensing. "Give us favorable terms, or we drop ARM from this design"

[irdc]

3b. Eventually, should ARM increase their prices, be able to produce a chip that only has the RISC-V cores but is otherwise 100% compatible with the RP2350. And thereby giving their clients the option of porting their software to RISC-V and shipping a single firmware image that runs on both older devices with the (now expensive) RP2350 and new devices with the (still cheap) RISC-V-only chip.

[jsheard]

The RP2350 already has an OTP bit which permanently disables the ARM cores when set, so they wouldn't even have to sacrifice their economies of scale in order to make that play. A RISC-V-only variant could be exactly the same hardware, just with the OTP pre-set at the factory.

[irdc]

Exactly. And should RISC-V turn out to have been a hype (which I don’t think, but I do recognise that convincing the various MBA types that think they make the world go ‘round is not a given) they can do the opposite.

Which is nice for a chip they plan to make up to the 2040’s.

[gary_0]

> And should RISC-V turn out to have been a hype

Over 10 billion RISC-V devices have shipped, including microcontrollers in millions of Western Digital storage devices, nVidia GPUs, etc. They have no reason to go back to ARM; in many cases it's not even possible as ARM is very restrictive about extensions to the ISA. RISC-V is here to stay.

What remains to be seen is if RISC-V makes it to the CPU big leagues and ends up powering smartphones and such.

[nadius]

im fascinated with the idea of using the same photomask for different "kind" of ICs

[jsheard]

Basically everyone does it, the economy of silicon design means it is very often cheaper to make one or just a handful of masks and then artificially disable features to create granular variants inbetween the actual hardware variants. It's also used to salvage defective dies, if the defect is in an optional part of the chip then they can disable that part and sell it anyway.

[klelatti]

This makes it sound as though

1. Arm can increase royalty rates on existing already shipping designs.

2. That increases in royalty rates would be material to the price paid by the end user - making the device ‘expensive’ for the end user.

Neither of these reflect the actual nature of licenses in practice.

[rcxdude]

If you're buying a large quantity of them for a product the license fees can certainly be relevant (As can, e.g. the number of pins on the package). I suspect it's there for that kind of customer.

[klelatti]

Sure and what is possible is that some users develop RISC-V based applications and RPi can offer a slightly cheaper version for those really price sensitive customers.

The comment I replied to was unduly alarmist though in suggesting Arm could make the Pico ‘expensive’ vs ‘cheap’ now with a royalty increase on an existing license.

[snvzz]

4. Make the chip attractive to those who favor RISC-V and would not buy it otherwise.

This includes myself. I'll always pick a RISC-V option over an ARM one, if I can do so for the purpose.

On that note, I have already ordered some rp2350-based development boards.

[mrlonglong]

Pimoroni does a very sweet rp2350 board with 16MB flash and 8MB PSRAM. It landed on my desktop a few days ago but I've not had a look at it yet. I might bring up a Rust-based operating system on it, I already have have it up and running in QEmu but it will need a lot of changes to even boot as the Hazard3 cores only supports machine and user modes, there's no paging.

[snvzz]

I now have a Bus Pirate 6 on its way as well :)

[mrlonglong]

I was shocked to discover the Hazard3 cores doesn't do floating point. It would have been quite nice to have that.