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

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:

\[V_{in} = \frac{D * (2^n - 1)}{V_{ref}}\]

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

\[V_{in} = \frac{D * (4095)}{1.8}\]

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

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:

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, /dev/i2c-1 Users can connect a new device to it via pins H1.43 (SCL) and H1.41 (SDA) of the CubeSat Kit Bus connectors.

I2C Standards Doc

Kubos Linux is currently configured to support the I2C standard-mode speed of 100kHz.

For examples and instructions, see the I2C HAL documentation.

Note

The I2C bus is available through the Kubos C HAL as K_I2C1.

RTC

The Pumpkin MBM2 has a real-time clock (RTC) which is used to maintain system time.

This clock can be queried or set using the hwclock command.

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 (SLIP) H1.20 H1.19 H1.12 H1.11

Users can interact with these ports using Linux’s termios interface.

A tutorial on this interface can be found here

The /dev/ttyS5 device has been preconfigured to be used for SLIP connections. Please refer to the SLIP instructions for more information.

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}’.

microSD

/home/microsd

This directory points to a partition on the microSD device included with the base Beaglebone Black board