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This framework supports Linux on several single board microcomputers. The goal of the MuntsOS project is to deliver a turnkey, RAM resident Linux operating system for very low cost single board microcomputers. With MuntsOS installed, such microcomputers can treated as components, as Linux microcontrollers, and integrated into other projects just like traditional single chip microcontrollers.
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 file system is unpacked into RAM and thereafter the system runs entirely in RAM. The kernel image file, including the compressed root file system, runs about 10 MB.
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:
The MuntsOS root file system can be extended at boot time using any of three mechanisms:
First, if /boot/tarballs exists, any gzip 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 files.
Second, 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 with MuntsOS. Packages should be built specifically for MuntsOS. (The .deb package file format is simply convenient to use, as it is supported by BusyBox.)
The GPIO Server extension package demonstrates how to build a Debian package that adds application specific software to MuntsOS.
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. Self-extracting shell archives placed in autoexec.d can reconfigure the system for special purposes and/or extend it by unpacking and installing programs and libraries to the root file system in RAM.
The LED example extension script demonstrates how to build a fairly elaborate shell archive that adds application specific software to MuntsOS. The Ada Internet Thermometer example programs demonstrate how to build a compiled extension program that runs a network service in the background.
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 one or more extension programs in /boot/autoexec.d, Debian package files in /boot/packages, and/or tarball files in /boot/tarballs.
Prebuilt MuntsOS extension packages, programs, and shell archives are available at:
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.
Prebuilt MuntsOS Thin Server .zip files are available at:
The consolidated Munts OS Thin Servers muntsos-BeagleBone.zip and muntsos-RaspberryPi.zip are now preferred for most purposes. They can be customized (including downloading extensions) by running the sysconfig program after the initial boot of the thin server.
Note: BeagleBone boards 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.
The BeagleBone was one of the first low cost Linux microcomputers. It originally sold for USD $89 at its launch in October 2011.
The BeagleBone has a Texas Instruments Sitara AM3359 processor running at 720 MHz and 256 MB of RAM. It has two USB port sockets: One type A host port and one type mini-B device port. Unlike any of its successors, the original BeagleBone has its USB device port connected to a USB hub instead of directly to the AM3359. Three distinct USB devices are visible to the host on the device port socket: The AM3359 device port, a USB JTAG device, and a USB serial port device connected to the AM3359 console serial port. The BeagleBone also has two PRU (Programmable Realtime Unit) I/O processors on board that are capable of very fast I/O operations.
MuntsOS includes device tree overlays than can be enabled by sysconfig that allow configuring any of the expansion header GPIO pins with config-pin. The system startup script /etc/rc will initialize GPIO pin modes according to /etc/pinmux.conf. By default, the following devices are are enabled on the two 46-pin expansion headers:
Newly manufactured BeagleBone boards assembled with a 1 GHz AM3358 processor are apparently available from Special Computing.
The BeagleBone Black is a cost reduced version of the BeagleBone. It currently sells for about USD $55. The BeagleBone Black originally sold for USD $45 at its launch in April 2013, which would have been an impressive feat except that the Raspberry Pi had already arrived on the market a few months earlier at USD $35. Although the BeagleBone Black was more capable than the first couple of Raspberry Pi generations, it has been overshadowed by the Raspberry Pi Model 2 and 3, which sport quad-core processors. The great strength of the BeagleBone Black and its kin compared to the Raspberry Pi family is the sheer number of GPIO pins and peripheral ports available on its two 46-pin expansion headers. Even after eMMC, I2C, SPI, and UART pins have been allocated, there are 42 GPIO pins available.
The BeagleBone Black has a Texas Instruments Sitara AM3358 processor running at 1 GHz, 512 MB of RAM and 4 GB eMMC flash on board. It uses the same kernel as the BeagleBone, with a different device tree.
Unlike the original BeagleBone (above) and the BeagleBone Green (below), the BeagleBone Black has an HDMI video output (though with a pesky micro HDMI connecteor). The HDMI interface consumes a large number of GPIO pins when it is enabled. This MuntsOS port does not enable the HDMI interface.
The BeagleBone Black Wireless is a variant of the BeagleBone Black that has replaced the wired Ethernet interface with a built-in Wifi radio. It also has replaced the mini-B slave USB receptacle with a more modern micro-B receptacle. It is otherwise highly compatible with the BeagleBone Black. It sells for about USD $70, considerably more than any of the other boards supported by MuntsOS, and also considerably more than a BeagleBone Green plus a USB WiFi adapter.
The BeagleBone Black Wireless uses the same kernel as the BeagleBone, with a different device tree.
MuntsOS does not currently support the on-board Bluetooth radio.
The BeagleBone Green is a cost reduced version of the BeagleBone Black, from Chinese manufacturer Seeed Studio, that sells for about USD $44. Changes from the BeagleBone Black design are:
The BeagleBone Green uses the same kernel as the BeagleBone, with a different device tree.
The BeagleBone Green is cost competitive with the Raspberry Pi, costing only a little more but including on board eMMC and a USB cable. It has only a single core processor, compared to the quad-core Raspberry Pi 3, but provides many more GPIO pins on its two 46-pin expansion headers. It also has separate dedicated host and slave USB ports as well as the two Grove sockets.
The BeagleBone Green plus a USB WiFi adapter is about USD $20 cheaper than a BeagleBone Black Wireless, while retaining the possibility for wired Ethernet.
The BeagleBone Green Wireless is a variant of the BeagleBone Green that has replaced the wired Ethernet interface with a built-in Wifi radio. It is otherwise highly compatible with the BeagleBone Green. It sells for about USD $53.
The BeagleBone Green Wireless uses the same kernel as the BeagleBone, with a different device tree.
MuntsOS does not currently support the on-board Bluetooth radio.
The BeagleBone Green Wireless is a mixed blessing: It has 4 USB ports and on-board WiFi, but commandeers quite a few of the expansion header GPIO pins for the on-board radios. Among other things, this seems to prohibit using SPI1. Also, the physical layout prevents using the BeagleBone Click Shield, which has some advantages over the newer mikroBus Cape.
The PocketBeagle is a cost and size reduced version of the BeagleBone Black. It currently sells for about USD $25 and is intended for the same market niche as the Rasperry Pi Zero. Although considerably more expensive than either version of the Raspberry Pi Zero, the PocketBeagle has many more I/O devices directly accessible from its expansion headers.
The PocketBeagle uses the same kernel as the BeagleBone, with a different device tree. The PocketBeagle device tree enables the following devices on its two 36-pin expansion headers:
The expansion headers are cleverly arranged such that the two inner rows match the MikroElektronika mikroBUS specification. If female sockets are installed on the top of the PocketBeagle, two Click Boards can be plugged directly into the expansion headers.
Like the Raspberry Pi Zero, the PocketBeagle comes without on-board eMMC, USB cable, micro-SD card, or expansion headers.
Unlike the Raspberry Pi Zero, the PocketBeagle expansion headers do not match its progenitors, so BeagleBone capes cannot be used on it.
The Raspberry Pi is a low cost Linux microcomputer selling for USD $5 to $35 (depending on model). Raspberry Pi 1 models have a BCM2835 ARMv6 single-core CPU running at 700 to 1000 MHz and come with with 256 MB to 512 MB of RAM. They have 10/100 Ethernet, 1 to 4 USB ports, HDMI, RCA composite video and a stereo headphone or three-pole A/V jack. They also have several miniature connectors for camera and LCD display modules as well as a single 26 or 40 pin 2.54 mm pitch GPIO expansion connector, to which expansion boards like this can be attached.
This MuntsOS port is regularly tested on the Raspberry Pi 1 Models A, B, A+, B+, CM1, Zero and Zero Wireless. All Raspberry Pi 1 models use the same kernel, with different device trees.
MuntsOS also provides a separate Raspberry Pi 1 kernel with dedicated USB Gadget support enabled. This kernel runs on the Models A, A+, CM1, Zero, and Zero Wireless and allows powering and communicating with a Raspberry Pi solely through the USB port. This kernel supports USB Network, Raw HID, and Serial Port gadgets, selected by bits in the OPTIONS word passed on the kernel command line. The USB Gadget Thin Servers have USB Network Gadget selected by default.
The absolute minimum possible usable Raspberry Pi kit consists of a Raspberry Pi Zero, a micro-USB cable, and a micro-SD card with one of the MuntsOS Raspberry Pi 1 Gadget Thin Servers installed.
The Rasbperry Pi 2 Model B is a greatly enhanced version of the Raspberry Pi, selling for about USD $35. It has a 900 MHz BCM2836 ARMv7 (BCM2837 ARMv8 on later production boards) quad-core CPU and comes with 1 GB of RAM. It is mechanically compatible with the Raspberry Pi 1 Model B+, with 10/100 Ethernet, 4 USB ports, 3.5 mm A/V jack, and a 40-pin GPIO expansion header.
The Rasbperry Pi 3 Model B is a greatly enhanced version of the Raspberry Pi, selling for about USD $35. It has a 1200 MHz BCM2837 ARMv8 quad-core CPU and comes with 1 GB of RAM. It is mechanically compatible with the Raspberry Pi 1 Model B+ and Raspberry Pi 2 Model B, with 10/100 Ethernet, 4 USB ports, 3.5 mm A/V jack, and a 40-pin GPIO expansion header. It also includes 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 port and no wired Ethernet. It runs at 1400 MHz and has 512 MB of RAM.
The Raspberry Pi 3 Model B+ runs at 1400 MHz and has improved power management and networking components.
All Raspberry Pi 3 models use the same 32-bit kernel and toolchains as the Raspberry Pi 2, with different device trees.
MuntsOS also provides a separate Raspberry Pi 2 kernel with dedicated USB Gadget support enabled that runs on the CM3 and the Raspberry Pi 3 Model A+.
This MuntsOS port enables the WiFi radio, but disables the internal Bluetooth radio, in favor of the serial port on the expansion header. If the internal WiFi radio seems intermittent, check the power supply voltage. The internal WiFi radio seems to be sensitive to drooping supply voltage.
I build a custom C/C++/Fortran/Ada cross-toolchain (using Linaro ABE) for each MuntsOS platform family. Each 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 C/C++ cross-toolchain.
I also build cross-toolchains for Free Pascal. These Pascal cross-toolchains rely on the libraries in the C/C++ cross-toolchain, which must be installed first.
Sometimes cross-toolchains can be shared among different platforms: For example, the Raspberry Pi 2 and Raspberry Pi 3 can use the same cross-toolchains (the ARMv7 cross-toolchains nominally built for the Raspberry Pi 2).
Cross-toolchain packages built for Debian 9 (Stretch) are available at:
Since they are statically linked, it may be possible to use these cross-toolchain packages on other Linux distributions (possibly with the help off a conversion utility like alien).
For the convenience of users of Linux distributions other than Debian, snapshot toolchain tarballs for each platform family are available at:
The source code for MuntsOS is available at:
Use the following command to clone it:
git clone https://github.com/pmunts/muntsos.git
Prebuilt binaries for MuntsOS are available at:
Original works herein are copyrighted as follows:
Copyright (C)2010-2019, Philip Munts, President, Munts AM Corp. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Redistributed works herein are copyrighted and/or licensed by their respective authors.
I am available for custom system development (hardware and software) of products based on embedded Linux microcomputers or other processors.