MuntsOS is a ferociously reduced Linux distribution for embedded systems. It runs on several microcomputer boards, including all 64-bit Raspberry Pi models, providing a turnkey RAM resident Linux operating system. With MuntsOS installed, a small and low cost Linux microcomputer becomes a Linux microcontroller, and can be integrated into an embedded system just like a single chip microcontroller but coming with a much, much richer development ecosystem.
Other embedded system Linux distributions such as Buildroot or Yocto Linux are very cumbersome and have very steep learning curves. If you are building a test fixture or process controller or almost any other embedded system that contains a Raspberry Pi board, MuntsOS offers a very high productivity development environment and a very easy to deploy target operating system.
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17 December 2024 -- Moved all 32-bit target deliverables (toolchain packages, kernels, extensions, and thin servers) to https://repo.munts.com/muntsos/attic. I did a final build of the 32-bit target kernels with
sysconfigmodified to fetch extensions from the attic. I do not anticipate ever building the 32-bit target kernels or thin servers again. -
20 December 2024 -- Upgraded the Raspberry Pi kernel to 6.6.67. Added a new device tree overlay,
Pi4ClickShield, to support the eponymous mikroBUS shield. -
26 December 2024 -- Added preliminary support for the Orange Pi Zero 2W. I have the U-Boot boot loader and the Linux mainline 6.12 LTS kernel, both with serial port console, working all the way to the login prompt. Much work on the kernel and device tree remains before MuntsOS on the Orange Pi Zero 2W is ready for production use.
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28 December 2024 -- I had to drop back to the manufacturer Linux 6.1 kernel tree for the Orange Pi Zero 2W. The Linux mainline 6.12 LTS tree does not have drivers for PWM outputs nor the built-in WiFi chipset, both of which are required for the application I have in mind. MuntsOS for the Orange Pi Zero 2W built on Linux 6.1 is about at the same point or a litte further along than what I had running on Linux 6.12 LTS. Most things seem to be working except HDMI and internal WiFi. I have been testing with a Broadcom WiFi Adapter and Two Port Hub I got years ago for the Raspberry Pi Zero.
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3 January 2025 -- Upgraded the Raspberry Pi Linux kernel to 6.6.69. Got the Orange Pi Zero 2W console on USB keyboard / HDMI monitor working. Modified
/etc/inittabto support four virtual terminals on HDMI video target platforms. Changed the kernel defaultprintkquiet priority level to 2, to suppress mostprintknoise to the console. Added support for importing settings from/etc/sysctl.conf. -
4 January 2025 -- Added
tclsh,expect, andsocatextension packages. Tcl is a scripting language that has been around in the Unix world for a very long time, since 1988.tclshis the Tcl interpreter program. Some years ago I used Tcl for text fixture automation, an application for which it is very well suited.expectis both an extension to Tcl and a standalone program that is extremely useful for automating a dialog between a computer and an I/O device with a serial port interface. All manner of older lab instruments and other industrial equipment had a serial port control interface, as do more modern devices such as the ESP8266 WiFi microcontroller. Many modern instruments, such as my oscilloscope, have a USB-B receptacle that enumerates as a serial port when plugged into a computer.socatis a Linux utility program that bridges two byte stream communications channels of various kinds, such asstdin/stdoutand a serial port, in the case of theexpectscript I was using to configure the ESP8266. -
8 January 2025 -- As I was preparing to begin work on USB Gadget mode for the Orange Pi Zero 2W, I realized that, unlike the Raspberry Pi 3, the Raspberry Pi 4 does not need a separate USB Gadget kernel. The old obsolete BeagleBones, the Raspberry Pi 4 Model B, and the Raspberry Pi 5 Model B all have a USB controller dedicated to the USB Mini-A/USB micro-A/USB-C power receptacle that is entirely separate from the USB controller dedicated to the USB-A receptacle(s). The BeagleBone family never needed a separate USB Gadget kernel and neither do the Raspberry Pi 4 or 5.
The direction (host or peripheral) of the Raspberry Pi 4 Model B (and the Raspberry Pi 5 Model B) USB-C receptacle is set in the device tree, by adding either
dtoverlay=dwc2,dr_mode=hostordtoverlay=dwc2,dr_mode=peripheralto/boot/config.txt. This may or may not work on CM4/CM5 carrier boards: The Compute Module 4 IO Board can be placed into USB peripheral mode but the Waveshare CM4-Duino cannot. Negotiating USB peripheral mode seems to require USB OTG (On The Go) configuration signals and/or resistors that are wired on the CM4 I/O Board but not on the CM4-Duino.This USB Gadget scheme works equally well on the Raspberry Pi 5 Model B and I have enabled support for USB Gadget mode in the Raspberry Pi 5 kernel. Both my Windows laptop and Dell tower running Debian Linux Bookworm are able to supply enough current to their USB-A receptacles to power up a Raspberry Pi 5 Model B with 4 GB of RAM running MuntsOS. YMMV.
Just for the fun of it, I have added the stress-ng extension package to MuntsOS see how a Raspberry Pi 5 Model B would hold up drawing power from the Dell tower's front panel USB-A receptacle.
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9 January 2025 -- Another big milestone for the Orange Pi Zero 2W: USB Gadget support is working. The Orange Pi Zero 2W has two USB-C receptacles. If you orient the board vertically, with the micro-SD receptacle at the top, the 40-pin expansion bus on the right, and the HDMI and USB-C receptacles on the left, the bottom USB-C receptacle (labeled
TYPEC1on the schematic diagram) is the USB peripheral receptacle and the one above it (labeledTYPEC2on the schematic diagram) is the USB host receptacle. You can supply power to either USB-C receptacle, but you will almost always want to use the lower one for power and tethering and the upper one for USB devices. -
31 January 2025 -- Upgraded the Raspberry Pi kernel to 6.6.74, mailutils to 3.18, and nano editor to 8.3.
Backed out the
link-gpiochiphack, since the Raspberry Pi team has since fixed the Raspberry Pi 5 GPIO compatibility issue. The Raspberry Pi 5 expansion header GPIO pins are back ongpiochip0like all previous Raspberry Pi models. See this Application Note for more information. -
12 February 2025 -- Added libgpiod to the toolchain libraries packages
gcc-*-muntsos-linux-gnu-ctng-libsand added the libgpiod runtime extension package. Because they use the sameioctl()services, libgpiod and libsimpleio interoperate without any problems. Note that this libgpiod is newer than that in Debian 12 (Bookworm), including Raspberry Pi OS. -
17 February 2025 -- Upgraded the .Net Runtime to 9.0.2. Upgraded the Raspberry Pi kernel to 6.6.78.
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20 February 2025 -- Crosstool-NG release 1.27.0 was published a few days ago. I have used it to build the 10th iteration of the MuntsOS cross-toolchain packages, upgrading binutils to 2.43, GCC to 14.2.0, and glibc to 2.41. GCC 14.2.0 includes support for Ada 2022 and a lot of Modula-2 fixes. All of the extensions, kernels, and thin servers have been rebuilt with the new GCC 14.2.0 toolchain. The previous GCC 13.2.0 cross-toolchain packages, extensions, kernels, and thin servers have been moved to the attic.
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23 February 2025 -- Added initial support for the 64-bit BeaglePlay. Next up will probably be the 64-bit VisionFive 2. I have already built a GCC 14.2.0
riscv64cross-toolchain for MuntsOS. -
6 March 2025 -- Finally got around to completing a couple of loose ends for the Raspberry Pi CM5 on a CM5IO. This has proven to be a very nice setup.
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13 March 2025 -- Support for the BeaglePlay is now done. See Application Note #19 for important information.
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18 March 2025 -- Enabled encryption for repo.munts.com (GitHub issue #2) which is now accessible either without encryption at http://repo.munts.com or with encryption at https://repo.munts.com. Document and script hyperlinks that formerly referenced git.munts.com now reference https://repo.munts.com/muntsos and
sysconfighas switched fromwgettocurl. -
22 March 2025 -- Overhauled MuntsOS email support: Rewrote Application Note #16, upgraded the
dmaandemailrelayextension packages to latest releases, and updated their configuration files for authenticated SMTP relay. Addedmailtunnel, an extension package template.
Instructions for installing the MuntsOS cross-toolchain development environment onto a development host computer are found in Application Note #1 and Application Note #2. Or just download and run one of the following quick setup scripts:
setup-debian
setup-fedora
setup-rhel
Instructions for installing MuntsOS to a target computer are found in Application Note #3 and Application Note #15.
The documentation for MuntsOS (mostly application notes) is available online at:
https://repo.munts.com/muntsos/doc
MuntsOS is a stripped down Linux distribution that includes a small compressed root file system within the kernel image binary itself. At boot time the root file system is unpacked into RAM and thereafter the system runs entirely in RAM. After MuntsOS has finished booting, it unmounts the boot media, so you don't have to worry about an orderly shutdown. Just power off the microcomputer board whenever you want to.
Each kernel release tarball contains a kernel image file (.img),
which may be common to several different microcomputer boards, and one
or more device tree files
(.dtb) that are specific to particular microcomputer boards. Some
kernel release tarballs also contain one or more device tree overlay
files (.dtbo) that can make small changes to the device tree at
boot time.
Prebuilt MuntsOS kernel release tarballs are available at:
https://repo.munts.com/muntsos/kernels
The MuntsOS root file system can be extended at boot time using any of three mechanisms:
First, if /boot/tarballs exists, any gzip'ed tarball files
(.tgz) in it will be extracted on top of the root file system.
Typically you would use this mechanism for customized /etc/passwd,
.ssh/authorized_keys, and similiar system configuration files.
Secondly, if /boot/packages exists, any Debian package files
(.deb) in it will be installed into the root file system. Note
that packages from the Debian project will
probably not work; they must be built specifically for MuntsOS. The
startup script that installs .deb packages also installs
.rpm and .nupkg packages.
Thirdly, the system startup script /etc/rc can be configured via a
kernel command line option to search for a subdirectory called
autoexec.d in various places, such as SD card, USB flash drive,
USB CD-ROM or NFS mount. If an autoexec.d subdirectory is found,
each executable program or script in it will be executed when the system
boots.
The idea is to build a MuntsOS kernel (which takes a long time) once
and install it to the target platform. Then application specific
software can be built after the fact and installed as tarball files in
/boot/tarballs; Debian, RPM, and NuGet package files in
/boot/packages; or executable programs and scripts in
/boot/autoexec.d.
Prebuilt MuntsOS extension packages are available at:
https://repo.munts.com/muntsos/extensions
The Thin Server is a system design pattern that is little more than a network interface for a single I/O device. Ideally, a Thin Server will be built from a cheap and ubiquitous network microcomputer like the Raspberry Pi. The software must be easy to install from a user's PC or Mac without requiring any special programming tools. It must be able to run headless, administered via the network. It must be able to survive without orderly shutdowns, and must not write much to flash media. It must provide a network based API (Application Programming Interface) using HTTP as a lowest common denominator.
MuntsOS, with its operating system running entirely from RAM, serves
well for the Thin Server, and the two concepts have evolved together
over the past few years. The simplest way to use MuntsOS is to
download one of the prebuilt Thin Server .zip files and extract it
to a freshly formatted FAT32 SD card. You can then modify
autoexec.d/00-wlan-init on the SD card to pre-configure it for
your wireless network environment, if desired, before inserting it in
the target board. After booting MuntsOS, log in from the console or
via SSH (user "root", password "default") and run
sysconfig to perform more system configuration.
Note: Some platforms require the boot flag to be set on the FAT32 boot partition on the SD card or on-board eMMC. The ROM boot loader in the CPU will ignore any partitions that are not marked as bootable.
MuntsOS Application Notes 3 and 15 contain more detailed instructions about how to install a MuntsOS Thin Server.
Prebuilt MuntsOS Thin Servers are at available at:
https://repo.munts.com/muntsos/thinservers
The BeaglePlay is a small Linux microcomputer board with industry standard interfaces for add-on I/O modules (a mikroBUS socket, a QWIIC socket, and a Grove socket) instead of a general purpose expansion header. It has a Texas Instruments AM6254 ARMv8 Cortex-A53 quad core CPU and comes with 2 GB of RAM. The BeaglePlay has one USB-A receptacle for peripheral devices and one USB-C receptacle for power and tethering. It has a 10/100/1000BASE-T wired Ethernet interface, a 10BASE-T1L single pair Ethernet interface (intended for a factory automation network and worthless for any other purpose), and a CC1352P7 wireless microcontroller capable of supporting a wide variety of radio networks. For more information read the target platform notes in Application Note #19.
The BeaglePlay has a couple of serious design defects: The AM6254 CPU hardware watchdog timers are unusable and the ADC102S051 A/D converter has only 10 bit resolution and lacks a Linux kernel driver.
You will need to edit /boot/config.txt to enable USB Gadget mode.
Change the OPTIONS word to 0x172C for a USB HID gadget,
0x072E for a USB Ethernet gadget, or 0x03AC for a USB serial
port gadget. See Application Note
#10 for more
information about the OPTIONS word.
The Orange Pi Zero 2W is a small Linux microcomputer with a form factor very similiar to the Raspberry Pi Zero 2 W, making it ideal for embedded system projects. It has a 1500 MHz Allwinner H618 ARMv8 Cortex-A53 quad-core CPU and comes with 1 to 4 GB of RAM and on-board Bluetooth and WiFi radios. It is available for sale on Amazon for $21.99 (1 GB RAM) to $33.99 (4 GB RAM). See Application Note #20 for more information.
The much larger RAM is a big advantage and I have been able to purchase as many as I want without limits when the Raspberry Pi Zero 2 W has been unavailable. Unfortunately, the manufacturer kernel source tree has not been maintained regularly and is currently at 6.1.31.
You will need to edit /boot/config.txt to enable USB Gadget mode.
Change the OPTIONS word to 0x172C for a USB HID gadget,
0x072E for a USB Ethernet gadget, or 0x03AC for a USB serial
port gadget. See Application Note
#10 for more
information about the OPTIONS word.
The Raspberry Pi is a family of low cost Linux microcomputers selling for USD $15 to $80, depending on model. There have been five generations of Raspberry Pi microcomputers, each using a successively more sophisticated Broadcom ARM core CPU. The first two generations (32-bit ARMv6 Raspberry Pi 1 and 32-bit ARMv7 Raspberry Pi 2) are now obsolete.
Some Raspberry Pi models have an on-board Bluetooth radio that uses the serial port signals that are also brought out to the expansion header. By default, MuntsOS port disables the on-board Bluetooth radio, in favor of the serial port on the expansion header.
All of the following 64-bit Raspberry Pi models use the same AArch64 cross-toolchain.
The Raspberry Pi 2 Model B Revision 1.2 with the 900 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU can be treated as a power conserving Raspberry Pi 3 Model B− and is useful for industrial applications where wired Ethernet is preferred.
The Rasbperry Pi 3 Model B has a 1200 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU and has 1 GB of RAM along with on-board Bluetooth and WiFi radios.
The Raspberry Pi 3 Model A+ has the same form factor as the Raspberry Pi 1 Model A+, with only one USB host receptacle and no wired Ethernet. It has a 1400 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU and has 512 MB of RAM along with on-board Bluetooth and WiFi radios.
The Raspberry Pi 3 Model B+ has a 1400 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU and has improved power management and networking components.
The Raspberry Pi Zero 2 W has the same form factor as the Raspberry Pi Zero W, with a 1000 MHz BCM2710 ARMv8 Cortex-A53 quad core CPU and 512 MB of RAM along with on-board Bluetooth and WiFi radios. This small, light, and inexpensive board is probably one of the best Linux microcomputers available for implementing embedded systems.
All Raspberry Pi 3 models use the same ARMv8 kernel, with different device trees.
MuntsOS also offers a second, different Raspberry Pi 3 kernel with USB host support disabled and USB Gadget peripheral support enabled. This kernel only runs on 3 A+, Zero 2 W, and certain CM3 carrier boards which lack the USB hub present on Raspberry Pi 3 Model B and B+ boards. The single USB controller that is part of the BCM2710 CPU is wired directly to the USB-A receptacle on the 3 A+ or the USB Micro-A receptacle on the CM3 I/O board or the Raspberry Pi Zero 2 W.
The Raspberry Pi 3 USB Gadget kernel supports USB Ethernet, Raw HID, and
Serial Port gadgets, selected by bits in the OPTIONS word passed
on the kernel command line (as configured in /boot/cmdline.txt).
See Application Note
#10 for more
information about the OPTIONS word. Raspberry Pi 3 USB Gadget Thin
Servers have USB Network Gadget selected by default.
You can supply power to and communicate with a compatible Raspberry Pi 3 (A+, CM3, or Zero 2W) running the USB Gadget kernel through the USB receptacle. The absolute minimum possible usable Raspberry Pi kit consists of a Raspberry Pi Zero 2 W, a micro-USB cable, and a micro-SD card with one of the MuntsOS Raspberry Pi 3 USB Gadget Thin Servers installed.
The Raspberry Pi 4 Model B has a 1500 MHz BCM2711 ARMv8 Cortex-A72 quad-core CPU and is available with 1 to 8 GB of RAM. It diverged significantly from the Raspberry Pi 1 B+ form factor, with the USB and Ethernet receptacles reversed, two micro-HDMI receptacles instead of a single full size HDMI receptacle, and a USB-C power receptacle instead of micro-USB. Two of the USB receptacles are 3.0 and two are 2.0. A major improvement is a Gigabit Ethernet controller connected via PCI Express instead of the USB connected Ethernet used for all earlier models. The Raspberry Pi 4 Model B uses the same wireless chip set as the 3+.
There are also a myriad of Raspberry Pi 4 Compute Modules, with varying combinations of wireless Ethernet, RAM and eMMC.
All Raspberry Pi 4 models use the same ARMv8 kernel, with different device trees.
You will need to edit some boot configuration files to enable USB Gadget
mode. First, change dtoverlay=dwc2,dr_mode=host to
dtoverlay=dwc2,dr_mode=peripheral in /boot/config.txt to
change the USB-C receptacle from USB host to USB peripheral. Then change
the OPTIONS word in /boot/cmdline.txt to 0x172C for a
USB HID gadget, 0x072E for a USB Ethernet gadget, or 0x03AC
for a USB serial port gadget. See Application Note
#10 for more
information about the OPTIONS word.
The Raspberry Pi 4 family consumes significantly more power than the Raspberry Pi 3 and not all host computers will be able to supply enough current to a single USB receptacle to support a Raspberry Pi 4 in USB Gadget mode.
The Raspberry Pi 5 Model B yields another 2-3x increase in performance over the Raspberry Pi 4, at the expense of greater power consumption. It has a 2400 MHz BCM2712 ARMv8 Cortex-A76 quad-core CPU and is available with 4 or 8 GB of RAM. The Ethernet receptacle and USB receptacles have swapped sides, so it has a form factor that is sort of a cross between the Raspberry Pi 1 B+ (same grouping of Ethernet and USB receptacles) and the Raspberry Pi 4 (same dual micro-HDMI receptacles and USB-C power receptacle).
There are also a myriad of Raspberry Pi 5 Compute Modules, with varying combinations of wireless Ethernet, RAM and eMMC.
All Raspberry Pi 5 models use the same ARMv8 kernel, with different device trees.
The Raspberry Pi 5 introduced a breaking PWM (Pulse Width Modulated)
output API change: It has four hardware PWM outputs on pwmchip2
(all previous Raspberry Pi models had two PWM outputs on pwmchip0)
with different pin mapping. Notably, PWM chip 2 channel 2 is mapped to
GPIO18 instead of PWM chip 0 channel 0 on previous Raspberry Pi boards.
See RP1
Peripherals
page 15 for more information.
You will need to edit some boot configuration files to enable USB Gadget
mode. First, change dtoverlay=dwc2,dr_mode=host to
dtoverlay=dwc2,dr_mode=peripheral in /boot/config.txt to
change the USB-C receptacle from USB host to USB peripheral. Then change
the OPTIONS word in /boot/cmdline.txt to 0x172C for a
USB HID gadget, 0x072E for a USB Ethernet gadget, or 0x03AC
for a USB serial port gadget. See Application Note
#10 for more
information about the OPTIONS word.
The Raspberry Pi 5 family consumes even more power than the Raspberry Pi 4 and not all host computers will be able to supply enough current to a single USB receptacle to support a Raspberry Pi 5 in USB Gadget mode.
I build a custom Ada/C/C++/Fortran/Go/Modula-2 GCC cross-toolchain for each MuntsOS platform family. Each GCC cross-toolchain requires a number of additional software component libraries, which are packaged and distributed separately but installed into the same directory tree as the parent cross-toolchain. I also build Free Pascal cross-compilers. Each of these rely on the libraries contained in the corresponding GCC cross-toolchain package.
Cross-toolchain packages built for Debian Linux (x86-64 and ARM64) development host computers are available at either:
https://repo.munts.com/debian12 (Debian package repository)
https://repo.munts.com/muntsos/toolchain-debs (just the package
files).
x86-64 RPM packages containing the exact same binaries, and known to work on Fedora 40 and RHEL 9.1 and its derivatives, are available at:
https://repo.munts.com/muntsos/toolchain-rpms
Alire Crates
Adding the muntsos_aarch64 crate to an Alire Ada program project
transforms said project into one that produces a cross-compiled AArch64
program for MuntsOS. See Application Note
#7
for a complete example using the alr command line tool.
muntsos_aarch64 depends upon the Linux distribution meta-package
muntsos-dev-aarch64 that in turn pulls in the rest of the
MuntsOS AArch64 cross-toolchain packages.
Please note that the other MuntsOS library crates in Alire (e.g.
muntsos_beaglebone) are unusable due to breaking changes in
alr 2.0. Unfortunately, Alire project policies prohibit removing
obsolete crates, so muntsos_beaglebone et al remain in the
repository as broken and abandoned orphans.
With the dotnet runtime extension installed, MuntsOS can run
architecture independent .Net programs produced by dotnet build,
dotnet publish, dotnet pack or the equivalent actions in
Microsoft Visual Studio. Many if
not most of the library packages published on
NuGet can be used in such programs.
The NuGet library package
libsimpleio provides
libsimpleio.dll, a .Net Standard 2.0 library assembly that binds
to the Linux shared library libsimpleio.so that is an integral
part of MuntsOS. The NuGet library package
libsimpleio-templates
provides a .Net Core console application project template
csharp_console_libsimpleio that, while not strictly necessary,
greatly simplifies creating an .Net Core console embedded system
application project for MuntsOS.
dotnet new install libsimpleio-templates
mkdir myprogram
cd myprogram
dotnet new csharp_console_libsimpleio
dotnet new sln
dotnet sln add myprogram.csproj
See Application Note
#8 for
a complete example using C# to flash an LED. See also the API
specification
for libsimpleio.dll.
The combination of Visual Studio + NuGet + libsimpleio.dll
delivers a very high productivity development environment for creating
embedded systems software to run on MuntsOS. With RemObjects
Elements, a commercial Visual
Studio addon product, you can even compile Object Pascal, Java, Go, and
Swift programs, all using libsimpleio.dll, to .Net program
assemblies that run on MuntsOS.
The source code for MuntsOS is available at:
https://github.com/pmunts/muntsos
Use the following command to clone it:
git clone https://github.com/pmunts/muntsos.git
Prebuilt binaries for MuntsOS (extensions, kernels, thin servers, and cross-toolchain packages) are available at:
https://repo.munts.com/muntsos
Questions or comments to Philip Munts phil@munts.net