Just how much bloat can you strip out of a Pi?

I get pretty good results with the latest version of devuan for the Pi.

does systemd have an equivalent of runlevel S ?

And how could I get rid of them?

None if you have systemd.

Alpine Linux is popular with containers, because it's extremely stripped down:

For non-Linux, you could try an alternative OS like RISC OS or FreeRTOS. You would need to port your apps to those OSes though - it wouldn't be a simple recompile.

Theo

If you want to cut out all of that, then you probably don't need the Pi at all. Have a look at an Arduino, you can either program bare metal, or if you don't want to do your own scheduling run under FreeRTOS.

---druck

RISC OS? Or possibly even RISC OS Pico.

Good use for an older Pi, as RISC OS doesn't need lots of RAM and is only a single core OS.

Bryan.

Free RTOS sounds...interesting

I need a fair bit of RAM and a pretty fast floating point processor. But Arduino has some definite pluses.

On Thu, 10 Sep 2020 12:47:40 +0100, The Natural Philosopher declaimed the following:

A microcontroller running barebones -- or with something like FreeRTOS (two tasks, with priority set as needed)?.

Especially as Linux is not the most "real-time" OS available; I don't even know if an RT kernel is available for the R-Pi (Beaglebones have had RT kernel builds, but they aren't the default install).

I believe there is a real time os in development somewhere - have you looked for it? You might also check out arch and gentoo,or maybe risc os.

On Thu, 10 Sep 2020 17:15:00 +0100, The Natural Philosopher declaimed the following:

So focus on the ARM-based boards, with an "f" suffix on the core -- M4F, say. TIVA-C boards, Adafruit Metro M4 (yeah, they don't list the F on the name, but do claim floating point and "DSP" instructions) and Grand Central M4. Unfortunately, the Arduino DUE does NOT appear to have hardware floating point.

Have a look at the Teensy 4.1 with 600 MHz cortex-m7 and room for extra memory:

Microware OS-9 could be a starter, since it was designed from the ground up as an RTOS.

It was originally released for the 6809 and quickly ported to the 680x0 where v2.4 was super-stable. Since then seems to have been ported to ARM and picked up TCP/IP support, but I can't determine which ARM architectures it has been ported to. Its website doesn't mention RaspberryPis either. Pity: I used it for years on a 68020 and liked it a lot.

And yes they have fp units. For doubles! From the 4.0 page, which has the same chip: "Teensy 4.0's Cortex-M7 processor includes a floating point unit (FPU) which supports both 64 bit "double" and 32 bit "float". With M4's FPU on Teensy 3.5 & 36, and also Atmel SAMD51 chips, only 32 bit float is hardware accelerated. Any use of double, double functions like log(), sin(), cos() means slow software implemented math. Teensy 4.0 executes all of these with FPU hardware."

Try PiCore, it's as stripped-down as Linux gets for the Pi. Boots _way_ quicker than RPi OS on my Pi Zeros. No GUI, or systemd, no disk access (runs in RAM). if you want to disable hardware drivers, you can do that in config.txt (as you can in Raspberry Pi OS).

There are various Bare-Metal environments, such as:

I cant find it for a Pi though sadly. Yes. OS-9 had its adherents. I have written my own multitasking OS under DOS 2...its not hard to write a basic scheduler good enough for simple work. In fact the application could easily run as one foreground task and one interrupt driven background task. But networking would be nice and that is a whole new can of worms...

Yes, that is near spec...

-- Those who want slavery should have the grace to name it by its proper name. They must face the full meaning of that which they are advocating or condoning; the full, exact, specific meaning of collectivism, of its logical implications, of the principles upon which it is based, and of the ultimate consequences to which these principles will lead. They must face it, then decide whether this is what they want or not.

Ayn Rand.

Ok I will take a look at that - may just be the 'right compromise' Mmm. At first glance that is very near the mark. AND I can prototype on an old PC *86 chassis...

You can start what you want. Linux is just the kernel. Alter the cmdline.txt to tell the kernel what program to start (init=...), instead of systemd or another init process.

see

Ok, your code that acts as init would have to start anything else you wanted, or set up networking etc. but it can be done. I'm pretty sure you could use busybox to form a minimal but adaptable boot environment.

This maybe of use...

All the parts are available from the standard Raspbian OS