Comment by blackkat | Hacker News Reader

Comment by blackkat | Hacker News Reader

Some specs here: https://www.digikey.ca/en/product-highlight/r/raspberry-pi/r...

Based on the RP2350, designed by Raspberry Pi in the United Kingdom

Dual Arm M33s at 150 MHz with FPU

520 KiB of SRAM

Robust security features (signed boot, OTP, SHA-256, TRNG, glitch detectors and Arm TrustZone for Cortex®-M)

Optional, dual RISC-V Hazard3 CPUs at 150 MHz

Low-power operation

PIO v2 with 3 × programmable I/O co-processors (12 × programmable I/O state machines) for custom peripheral support

Support for PSRAM, faster off-chip XIP QSPI Flash interface

4 MB on-board QSPI Flash storage

5 V tolerant GPIOs

Open source C/C++ SDK, MicroPython support

Software-compatible with Pico 1/RP2040

Drag-and-drop programming using mass storage over USB

Castellated module allows soldering directly to carrier boards

Footprint- and pin-compatible with Pico 1 (21 mm × 51 mm form factor)

26 multifunction GPIO pins, including three analog inputs

Operating temperature: -20°C to +85°C

Supported input voltage: 1.8 VDC to 5.5 VDC

> Low-power operation

Low power suspend? In a Pi Foundation product? Impossible.

Not sure why this is downvoted but the sleep and dormant pico examples have quite some issues, they are still in "extras" and not in "core", so while documentation of features is my personal favorite aspect of the pico, there is room for improvement here still.

It is downvoted because it is a low effort sarcastic comment which provides no real contribution to the discussion. Your comment actually provides real feedback as to where there are currently issues.

Hazard3 RTL: https://github.com/Wren6991/Hazard3

I wonder how well it's been verified.

This is a really big deal. Verifying a core is hard, and if the repo doesn't come with a testbench, I'm very suspicious.

Even if it does I'm suspicious. The open source RISC-V verification systems are not very good at the moment:

* riscv-arch-tests: ok, but a very low bar. They don't even test combinations of instructions so no hazards etc. * riscv-test: decent but they're hand-written directed tests so they aren't going to get great coverage * TestRig: this is better - random instructions directly compared against the Sail model, but it's still fairly basic - the instructions are completely random so you're unlikely to cover lots of things. Also it requires some setup so they may not have ran it.

The commercial options are much better but I doubt they paid for them.

See https://github.com/Wren6991/Hazard3/tree/stable/test for the test harnesses used. I wonder if they did release all they used there.

Wow, can't wait. Love the 5V GPIO and security features.

5V GPIO is a huge deal for me - this immediately opens up a huge range of integrations without having to worry about line level conversion.

I can’t wait to use this!

Does tolerant mean ok to do? Or it just won’t fry your chip but you should actually run at 3.3?

It usually means it's clamped so it might result in a small amount of wasted energy/heat but no damage.

So yes it means it's okay but if you can you should go for 3.3.

5V tolerant means that it'll accept 5V input (and correctly interpret it as high), but output will still be 3.3V.

Be careful with assumptions though. Being 5V tolerant doesn't mean that your 3V output can sufficiently drive an input that expects 0-5V levels correctly.

I ran into this problem using an ESP32 to drive a Broadcom 5V LED dot-matrix display. On paper everything looked fine; in reality it was unreliable until I inserted an LS245 between the ESP and the display.

> LS245

Do you think that would be a good IC to drive these with a RP2040? https://www.analog.com/en/products/max7219.html

A better question might be why anyone is using a MAX7219 on a new design in 2024. There are so many other choices for displays than a 20 year-old IC from a company that's gone through two changes of ownership since.

Anyway, a 74LS245 isn't a level shifter, it's an octal buffer. It just happened to be the right choice for my needs. In your application, I'd suggest an actual level shifter. You can find level shift breakout boards at Sparkfun and Adafruit.

> Being 5V tolerant doesn't mean that your 3V output can sufficiently drive an input that expects 0-5V levels correctly.

It's fine for TTL (like your 74LS245 is), which registers voltages as low as 2V as a logical 1. Being able to directly interface with TTL eases up so many retrocomputing applications.

Which was... exactly the reason I chose it?

I'm having trouble seeing where the datasheet actually says the GPIO pins are 5V tolerant.

EDIT: okay, section 14.8.2.1 mentions two types of digital pins: "Standard Digital" and "Fault Tolerant Digital", and the FT Digital pins might be 5V tolerant, it looks like.

Page 13: "GPIOs are 5 V-tolerant (powered), and 3.3 V-failsafe (unpowered)"

Yep, I edited a few minutes ago to mention a reference I found in the datasheet. It's cool, but the reality seems a little more nuanced than that quote would indicate, since that only appears to work for GPIO-only pins, not just pins being used as GPIO. (So, if a pin supports analog input, for example, it will not be 5V tolerant.)

Edit: See comment below; The RP2350 can be powered by a 5V supply.

I'd rather have it run on the lower voltage - generally easier to step down than buck up. Either way, the modules are pretty cheap, small, and easy to find.

How much tolerance does that have - can it run directly off a 3.7v lithium ion battery?

Yep, they explicitly call out that the onboard voltage regulator can work with a single lithium ion cell.

The regulator can take that, but as far as I can see it's only for DVDD, the core voltage of 1.1 V. You also need at least IOVDD, which should be between 1.8 V and 3.3 V. So you'll need to supply some lower voltage externally anyway.

I suppose the main draw of the regulator is that the DVDD rail will consume the most power. 1.1 V is also much more exotic than 3.3 V.

To clarify: You can connect a 5V power source by connecting it to the VSYS pin which leads into the on-board voltage regulator.

But the µC itself runs on 3.3V and is not totally 5V-capable. You'd need level converters to interface with 5V.

You're right, after re-reading the Power section on the datasheet it seems connecting 5V to the VREG_VIN should suffice to power the digital domains, but if you want to use the ADC, you still need a external 3.3V source.

Maybe not even that:

> A separate, nominally 3.3 V, low noise supply (VREG_AVDD) is required for the regulator’s analogue control circuits.

It seems it would be painful trying to run this without 3.3 V.

See section on physical pin gpio electrical tolerances.

The TL;DR is that 3.3v must be fed into IOVDD for 5.5v tolerance to work.

It's quite a bit more complicated.

The chip needs a) 1.1V to power the cores, b) 1.8V-3.3V to power IO, and c) 3.3V to properly operate USB and ADC.

The chip has one onboard voltage regulator, which can operate from 2.7V-5.5V. Usually it'll be used to output 1.1V for the cores, but it can be used to output anything from 0.55V to 3.3V. The regulator requires a 3.3V reference input to operate properly.

So yeah, you could feed the regulator with 4-5V, but you're still going to need an external 5V->3.3V converter to make the chip actually operate...

>You'd need level converters to interface with 5V.

Part of the GPIOs are CMOS are 5v-tolerant, and TTL considers 2v HIGH, thus it is possible to interface some 5v hardware directly.

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