Working with the Pumpkin MBM2¶
Overview¶
This document covers the Kubos Linux features which are specific to the Pumpkin MBM2 target.
Please refer to Using Kubos Linux for a general guide to using Kubos Linux.
Reference Documents¶
Pumpkin Documentation¶
The CubeSat Kit Motherboard Module (MBM) 2 reference document is available from Pumpkin and is a useful document for learning what each of the hardware components are and how they are connected.
Kubos Documentation¶
- Getting Started with Kubos Linux and the Kubos SDK - Basic tutorial for creating your first Kubos SDK project
- Kubos SDK Cheatsheet - Overview of the common Kubos SDK commands
- Using Kubos Linux - General guide for interacting with Kubos Linux
- Building Kubos Linux for the Pumpkin MBM2 - Steps to build Kubos Linux for the Pumpkin MBM2
- Installing Kubos Linux on a Pumpkin Motherboard Module 2 - Steps to install Kubos Linux
Status LEDs¶
There are four LEDs present on the Pumpkin MBM2 which give some indication of what state the board is in. When there is only one blinking LED, the board is running Kubos Linux and the system is currently idle. The LEDs will blink in correspondence with CPU and MMC activity. If all LEDs are solid, then the system has reached some kind of locked error state.
USB Connection¶
The Pumpkin MBM2 should be shipped with a USB Debug Adapter board.
The white connection cable should be plugged into the labeled “UART0” port on the edge of the board, with the exposed pins facing up.
The USB cable can then be plugged into your computer. Any required drivers should be automatically installed.
This connection will be passed through to a Kubos Vagrant image as /dev/FTDI and will be used for the serial console.
Peripherals¶
The Pumpkin MBM2 has several different ports available for interacting with peripheral devices. Currently, users should interact with these devices using the standard Linux functions. A Kubos HAL will be added in the future to abstract this process.
ADC¶
The Pumpkin MBM2 has seven analog input pins available:
| Name | Pin |
|---|---|
| AIN0 | H2.8 |
| AIN1 | H2.7 |
| AIN2 | H2.6 |
| AIN3 | H2.5 |
| AIN4 | H2.4 |
| AIN5 | H2.3 |
| AIN6 | H2.2 |
The pins are available through the Linux device /sys/bus/iio/devices/iio\:device0/.
A single raw output value can be read from each of the pins via
/sys/bus/iio/devices/iio\:device0/in_voltage{n}_raw, where {n} corresponds to the
AIN number of the pin.
Information about setting up continuous data gathering can be found in this guide from TI.
To convert the raw ADC value to a voltage, use this equation:
Where:
- \(D\) = Raw ADC value
- \(n\) = Number of ADC resolution bits
- \(V_{ref}\) = Reference voltage
The Pumpkin MBM2 uses 12 resolution bits and a reference voltage of 1.8V, so the resulting equation is
Ethernet¶
The Pumpkin MBM2, via the embedded Beaglebone Black, provides an ethernet port which can be used for things like inter-system communication.
The ethernet port is configured to have support for static IPv4 addressing and can be used with SSH via the included Dropbear package.
Kubos Linux currently guarantees support for TCP, UDP, and SCTP. Other protocols might be supported by default, but have not been verified.
Resources¶
- Kubos Ethernet Communication Guide
- TCP tutorial
- UDP tutorial
- SCTP tutorial
- Packet Sender - A tool to send test packets between an OBC and a host computer
Note
By default, Windows Firewall will block many incoming packet types. This may impact testing.
Configuration¶
The static IP address can be updated by editing the /etc/network/interfaces file.
By default the address is 10.0.2.20.
Examples¶
A couple example programs using the ethernet port can be found in the examples folder of the kubos repo:
- kubos-linux-tcprx - Receive TCP packets and then reply to the sender
- kubos-linux-tcptx - Send TCP packets to specified IP address and port
GPIO¶
The CSK headers have 6 GPIO pins available for use. These pins can be dynamically controlled via the Linux GPIO Sysfs Interface for Userspace as long as they have not already been assigned to another peripheral.
| CSK Pin | Linux GPIO Value | Direction |
|---|---|---|
| H1.6 | 65 | Input |
| H2.18 | 61 | Output |
| H2.21 | 89 | Output |
| H2.22 | 87 | Output |
| H2.23 | 86 | Output |
| H2.24 | 85 | Output |
CLI and Script Interface¶
To interact with a pin from the command line or from a script, the user will first need to generate the pin’s device name:
$ echo {pin} > /sys/class/gpio/export
For example, to interact with pin H2.18, which corresponds with GPIO_61, the user will use:
$ echo 61 > /sys/class/gpio/export
Once this command has been issued, the pin will be defined to the system as ‘/sys/class/gpio/gpio{pin}’. The user can then set and check the pins direction and value.
Set pin as output:
$ echo out > /sys/class/gpio/gpio61/direction
Set pin's value to 1:
$ echo 1 > /sys/class/gpio/gpio61/value
Get pins's value:
$ cat /sys/class/gpio/gpio61/value
Once finished, the pin can be released:
$ echo {pin} > /sys/class/gpio/unexport
Application Interface¶
This functionality can also be used from a user’s application with Linux’s sysfs interface.
An example program might look like this:
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int fd;
int pin = 61;
int value = 1;
/* Define the pin to the system */
fd = open("/sys/class/gpio/export", O_WRONLY);
write(fd, &pin, sizeof(pin));
close(fd);
/* Set the pin's direction */
fd = open("/sys/class/gpio/gpio45/direction", O_WRONLY);
write(fd, "out", 3);
close(fd);
/* Set the pin's value */
fd = open("/sys/class/gpio/gpio45/value", O_WRONLY);
write(fd, &value, 1);
close(fd);
/* Read the value back */
fd = open("/sys/class/gpio/gpio45/value", O_RDONLY);
char strValue[3];
read(fd, strValue, 1);
value = atoi(strValue);
close(fd);
/* Release the pin */
fd = open("/sys/class/gpio/unexport", O_WRONLY);
write(fd, &pin, sizeof(pin));
close(fd);
I2C¶
The Pumpkin MBM2 has one user-accessible I2C bus. Users can connect a new device to it via pins H1.43 (SCL) and H1.41 (SDA) of the CubeSat Kit Bus connectors.
Kubos Linux is currently configured to support the I2C standard-mode speed of 100kHz.
The I2C bus is available through the Kubos HAL as K_I2C1.
For examples and instructions, see the I2C HAL documentation.
UART¶
The Pumpkin MBM2 has 5 UART ports available for use in varying capacities:
| Linux Device | TX Pin | RX Pin | RTS Pin | CTS Pin |
|---|---|---|---|---|
| /dev/ttyS1 | H1.18 | H1.17 | H1.10 | H1.9 |
| /dev/ttyS2 | H1.8 | H1.7 | ||
| /dev/ttyS3 | H1.5 | |||
| /dev/ttyS4 | H1.16 | H1.15 | ||
| /dev/ttyS5 | H1.20 | H1.19 | H1.12 | H1.11 |
Users can interact with these ports using Linux’s termios interface.
User Data Partitions¶
The Pumpkin MBM2 has multiple user data partitions available, one on each storage device.
eMMC¶
The user partition on the eMMC device is used as the primary user data storage area. All system-related /home/ paths will reside here.
/home/system/usr/bin¶
All user-created applications will be loaded into this folder during the
kubos flash process. The directory is included in the system’s PATH,
so applications can then be called directly from anywhere, without
needing to know the full file path.
/home/system/usr/local/bin¶
All user-created non-application files will be loaded into this folder
during the kubos flash process. There is currently not a way to set
a destination folder for the kubos flash command, so if a different
endpoint directory is desired, the files will need to be manually moved.
/home/system/etc/init.d¶
All user-application initialization scripts live under this directory. The naming format is ‘S{run-level}{application}’.