From Newsgroup: comp.sys.raspberry-pi

On Mon, 2026-01-12 at 10:57 +0000, Gordon Henderson wrote:

like to know how to do it baremetal with ARM thumb assembly.

... my use is the RISC-V cores in the rp2350, so bare metal RISC-V asembly.... But the principle for programming the PWM generators
is more or less the same from eith CPU, so I understand, but it's
something I've not gotten round to.

I'd suggest to have a look at the manual and SDK and see how to do it
from C then hand translate the C code into ASM...

I've found the following: https://github.com/thejpster/rp-hal-rp2350-public/blob/main/rp235x-hal/examples/pwm_blink.rs
Looks like this is what I've been looking for.
The funny thing is that the Pimoroni tiny2040 that I also have has a
RGB LED on it, there's no data sheet for it but it appears to be
reversed, in that all the GPIO pins attached to this LED are all active
low, (i.e ~R GPIO18, ~B GPIO19, ~G GPIO20) so works in the opposite way
to the LED on GPIO 25 on rp2040!
--
Tactical Nuclear Kittens
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From Newsgroup: comp.sys.raspberry-pi

On Sun, 2026-01-11 at 18:52 +0000, Daniel James wrote:

However: There is a section on hardware PWM in the Pico-series C/C++
SDK, have you seen that?

Oh interesting, I can take a look at that. Hopefully the sources will
clarify what's required.

I confess it's not something I've played with, but it doesn't look
too impenetrable ... it doesn't require PIO programming (something
else I haven't played with yet) like another example I found.

No, you're right, thankfully I don't need to go down that PIO rabbit
hole yet. Just to demysterify how to do the PWM in assembly.

I'm not sure how long ago I downloaded this SDK so it may not be
quite current ... but it's section 4.1.18 on P249.

If you used a capable search engine you might stumble across this:

https://forums.raspberrypi.com/viewtopic.php?t=344634

which seems to shed some light ...

Thanks.
--
Tactical Nuclear Kittens
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From Newsgroup: comp.sys.raspberry-pi

On Sun, 2026-01-11 at 19:36 +0000, The Natural Philosopher wrote:

From: https://www.raspberrypi.com/documentation/pico-sdk/hardware.html#group_hardware_pwm

Excellent, I missed that one.
Thanks,
Alex
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Tactical Nuclear Kittens
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From Newsgroup: comp.sys.raspberry-pi

On 2026-01-17, Single Stage to Orbit <alex.buell@munted.eu> wrote:

I'd suggest to have a look at the manual and SDK and see how to do it
from C then hand translate the C code into ASM...

I've found the following:

https://github.com/thejpster/rp-hal-rp2350-public/blob/main/rp235x-hal/examples/pwm_blink.rs

Why not go to the primary source?

I believe the RP2xx0 datasheet has all you need in the PWM chapter (CH 4.5
for RP2040, or CH 12.5 for RP2350).

There is a list of registers with all the relevant bits explained.

The funny thing is that the Pimoroni tiny2040 that I also have has a
RGB LED on it, there's no data sheet for it but it appears to be
reversed, in that all the GPIO pins attached to this LED are all active
low, (i.e ~R GPIO18, ~B GPIO19, ~G GPIO20) so works in the opposite way
to the LED on GPIO 25 on rp2040!

This is quite common - they probably used a 4-pin LED package with common anode, so you have to drive the individual lines low to activate the LED.
You could use 3 external inverters or transistors to make them active high,
but why bother (the parts cost money and take up PCB space) when all it
takes to fix this is a single line of code on the software side?

cu
Michael
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Some people have no respect of age unless it is bottled.
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From Newsgroup: comp.sys.raspberry-pi

On 17/01/2026 15:21, Single Stage to Orbit wrote:

The funny thing is that the Pimoroni tiny2040 that I also have has a
RGB LED on it, there's no data sheet for it but it appears to be
reversed, in that all the GPIO pins attached to this LED are all active
low, (i.e ~R GPIO18, ~B GPIO19, ~G GPIO20) so works in the opposite way
to the LED on GPIO 25 on rp2040!

Did you read Pimoroni's own website entry for that part?

https://shop.pimoroni.com/products/tiny-2040

where it says:

*Notes*

* The RGB LED is connected to GP18-GP20 and active low (so the
on/off state will work in the opposite way to the LED on a
Raspberry Pi Pico). You can PWM the pins to dim the LED - check
out Tonygo2's MicroPython example.

The example cited is Python, so not directly of use to you, but here is
the link, anyway:

https://forums.pimoroni.com/t/tiny-2040-rgb-led-control-tutorial/16604
--
Cheers,
Daniel.
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