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DCFurs Badge Scripts

The DC26 DefCon Furs badge is running a micropython environment that allows you to script the badge to do awesome things.

Features Include

  • STM32F411RET6 microcontroller running Micropython
  • 32 Mbit SPI flash on SPI bus 3
  • 18x7 pixel LED matrix display
  • Two pushbutton switches located on the ears
  • Taiyo Yuden EYSGCNZ bluetooth radio connected to USART1
  • I2C bus 1 for sensors, including:
    • NXP MMA7660 accelerometer at address 0x4C
    • Azoteq IQS231A capacative touch controller at address 0x44
    • #badgelife shitty addon connector

Further Reading

Badge Module

The badge module is implemented in badge.py and contains all the setup necessary to bring your badge to life and operate the peripherals correctly. It is recommended that you initialize your badge properly by adding an import badge statement at the top of your main.py script.

badge.imu

This contains an instance of the MMA7660 accelerometer, which has been configured to perform wakeup and tap detection on the badge. The accelerometer is also available for orientation detection. Please refer to the micropython documentation for the API to the pyb.Accel class.

badge.ble

This contains an instance of the pyb.UART class, and is configured to communicate to the Taiyo Yuden EYSGCNZWY bluetooth module.

badge.boop

This contains a class dedicated to driving the IQS231A capacative sense controller, it provides an event() method that returns True when a capacative touch has been detected.

badge.trysuspend()

Check if the badge is in a state that can be put to standby mode, when in this state the LED matrix and CPU will be disabled, and the accelerometer will be configured as a wakeup source. Upon waking up from standby mode the CPU will perform a hard reset.

The badge will enter standby if all of the following conditions are met:

  • No voltage is detected on the VBUS pin (ie: USB disconnected)
  • No motion has been detected by the accelerometer in the last settings.sleeptimeout milliseconds

Settings Module

The settings module is implemented in settings.py and contains a collection of tunable parameters on how you want your badge to operate, such as the default animation to play on bootup and how long of a timeout to use before going to sleep.

DCFurs Module

The dcfurs module is impleneted within the Micropython firmware, and and includes the DMA and interrupt handlers necessary to drive the LED matrix. By writing this module in C, we can acheive a sufficiently fast scan rate to perform up to 64-steps of per-pixel dimming control.

Pixels in the matrix are addressed by their row/column coordinates, starting from row zero and column zero in the upper left corner of the matrix.

dcfurs.init(timer)

Initialize the LED matrix and DMA interrupt handlers, this must be called first before any other features in the DCFurs module can be used. The timer parameter provides a handle to the STM32 Advanced-function timer TIM1, configured at the desired PWM frequency. This timer will be used to provide interrupts and DMA transfers in order to refresh the delay.

    import dcfurs
    from pyb import Timer

    pwmclk = pyb.Timer(1, freq=125000)
    dcfurs.init(pwmclk)

dcfurs.clear()

Clear the LED matrix, setting all pixels to an off state.

dcfurs.set_row(row, pixels)

Set the pixels for an entire row using a bitmap of pixel on/off values. The pixels parameter can contain an integer, which will act as a bitmask of the pixels for this row, or an bytearray of PWM intensities.

dcfurs.set_pixel(row, col, value=True)

Sets the intensity of a single pixel using its row and column coordinates in the matrix. The value parameter can provide a PWM intensity value. Integer values in the range of zero to 256 control the intensity of the pixel, otherwise the truth value will either set the pixel to full intensity, or switch it off.

dcfurs.set_frame(fbuf)

Sets the entire frame buffer in a single call. The fbuf parameter should be an array exactly dcfurs.nrows in length, each elemnent of which describes one row of the matrix. If the row is an integer, it is interpreted as a bitmap that would be passed to dcfurs.set_row(), or if the row is a bytearray then it will be interpreted as an array of PWM intensity values.

This function can be implemented as a slightly more efficient version of:

    def set_frame(fbuf)
        i = 0
        for row in fbuf:
            set_row(i, row)
            i += 1

dcfurs.has_pixel(row, col)

Checks if the pixel at the given row and colum exists in the LED matrix. Due to the shape of the badge, some of the pixels at the corners of the matrix and over the bridge of the nose are missing from the display. This function will return True if the pixel exists and False otherwise.

dcfurs.nrows

This constant integer defines the number of rows in the LED matrix. This will have a value of 7.

dcfurs.ncols

This constant integer defines the number of columns in the LED matrix. This is will have a value of 18.

Badge Animations

Badge animations can be written as Python classes, or can be provided as JSON frame data. The resulting animations will be included as part of the animations module, with each class in this module providing a unique animation.

Every class provided by this module must present the following interface.

draw()

This mandatory method is called to render the next frame of the animation to the LED matrix.

interval

This mandatory variable must be provided by the animation to define the time, in milliseconds until the next call to the draw() method.

boop()

The animation may override the default behavior of the capacative touch events by defining a boop() method. This optional method will be called once for each touch event detected.

Python Animations

Badge animations written in python should be placed in the animations/ directory, and must implement both the draw() method and set the interval variable. We can write a simple row-scanning example as follows:

    import dcfurs

    class example:
        def __init__(self):
            self.counter = 0
            self.interval = 500
        
        def draw(self):
            self.counter += 1
            dcfurs.clear()
            dcfurs.set_row(self.counter % dcfurs.nrows, 0x3ffff)

To add your animation to the default set provided by the badge, you must add an import statement to animations/__init__.py

    from animations.example import example

From a REPL console, you can now run your animation with a simple python loop.

    import animations

    test = animations.example()
    while True:
        test.draw()
        pyb.delay(test.interval)

JSON Animations

For simple animations that don't require user interraction, the frames can also be provided in JSON format. These animations should be placed in the animations/ directory and named with a .json file extension. During initialization the animations module will generate class definitions for each JSON file found.

The JSON file should contain an array, with each element of the array containing a JSON object that defines an interval encoded as an integer, and a frame encoded as a string. The string should be a hexadecimal representation of the PWM intensity for each pixel, with rows delimited by a colon ':'. One nibble is given for each pixel, with a value of 0 turning the pixel off and F setting the pixel to full intensity.

Thus a single frame which shows PWM intensity increasing from right to left and top to bottom can be encoded as:

    [
        {
            "interval": 1000,
            "frame": "000000000000001234:000000000000123456:000000000012345678:00000000123456789a:000000123456789abc:0000123456789abcde:00123456789abcdeff"
        }
    ]

Recovery and Programming Modes

If something has gone wrong with your badge, don't panic! There are many ways to recover the state of your firwmare.

During power on, the two pushbuttons switches on the ears can be used to select the boot mode of the badge firmware. Switch SW1 is located on the left ear, adjacent to the shitty addon header and puts the badge into DFU bootloader mode. Switch SW2 is located on the right ear opposite the shitty addon header, and puts the badge into safe mode or performs factory recovery.

Safe Mode and Recovery

If switch SW2 is pressed during power on, the LED on the back of the badge will begin to cycle through three colors: Green, Blue and Cyan to select the boot mode. To select a boot mode, wait until the desired color is active and then release SW2. The badge will flash your selected mode and then proceed to boot.

  • Green selects normal boot mode, which mounts the filesystem and executes boot.py and main.py
  • Blue selects safe mode, which mounts the filesystem but does not execute boot.py or main.py
  • Cyan performs a factory recovery, which formats the filesystem and restores the default contents.

Updating Firmware

The STM32F411 microcontroller features a DFU bootloader, which is capable of updating its firmware via USB. From a Linux or OSX machine, you will need the firmware.dfu image, as well as the dfu-util program. To apply a firwmare update, perform the following steps.

  1. Completely power down the badge by removing the batteries and USB power.
  2. Power on badge via USB while holding down switch SW1, located adjacent to the shitty addon header.
  3. Execute the command dfu-util -a 0 -d 0483:df11 -D firmware.dfu. Note that this may require sudo depending on your operating system and USB permissions.
  4. Wait for the upgrade to complete, which may take up to 30 seconds.
  5. Unplug the badge from USB to restart and apply the firmware update.