Lua API
Lua is a tiny and extensible scripting language that’s designed to be power efficient and quick to learn. Frame features a complete Lua virtual machine based on the latest public release of Lua. Dedicated hardware APIs allow direct access to all of Frame’s peripherals at a high level so that developers can start building apps quickly and easily.
There’s no special cables or setup needed. Lua on Frame is accessed solely over Bluetooth, such that any user created host app can easily execute scripts by simply pushing Lua strings to the device.
To learn more how the underlying Bluetooth communication with Frame works, check out the Bluetooth section of the Building Apps page.
Library reference
This page describes all of the Frame specific Lua APIs available to the developer along with some helpful examples. Certain libraries allow for more low level access that can be used for debugging and hacking the various subsystems of Frame.
The API specification is still undergoing heavy development. Some of them may change over the coming month or so.
Display
The display engine of allows drawing of text, sprites and vectors. These elements can be layered atop one another simply in the order they are called, and then be displayed in one go using the show() function.
The Frame display is capable of rendering up to 16 colors at one time. These colors are preset by default, however each color can be overridden by any 8bit YCbCr color using the palette command.
| API | Description |
|---|---|
frame.display.palette{} | Details coming soon |
frame.display.text(string, x, y, {color='WHITE', align='TOP_LEFT'}) | Prints the given string to the display at x and y. A color can optionally be provided to print the text in one of the 16 palette colors, and align can optionally be provided to jutify the text as either 'TOP_LEFT', 'TOP_CENTER', 'TOP_RIGHT', 'MIDDLE_LEFT', 'MIDDLE_CENTER', 'MIDDLE_RIGHT', 'BOTTOM_LEFT', 'BOTTOM_CENTER', or 'BOTTOM_RIGHT' |
frame.display.bitmap() | Details coming soon |
frame.display.vector() | Details coming soon |
frame.display.show() | Shows the drawn objects on the display |
Example
-- Display 'Hello world' at x = 50 and y = 100
frame.display.clear()
frame.display.text('Hello world', 50, 100)
frame.display.show()
Camera
The camera capability of Frame allows for capturing and downloading of single JPEG images over Bluetooth. The sensor’s full resolution is 1280x720 pixels in portrait orientation, however only square images up to 720x720 pixels can be captured at a time. The user can select which portion of the sensor’s window is captured using the pan control. Additionally, the resolution of the capture can be cropped to either 360x360, 240x240 or 180x180 by using the zoom function. Smaller resolutions will increase the image quality, however the quality factor can be reduced to decrease the image file size, and increase download speeds of the image over Bluetooth.
| API | Description |
|---|---|
frame.camera.auto(enable, metering_mode) | Enables automatic exposure and whitebalance when enable is set to true. When enabling, mode can be given as either 'spot', 'center_weighted' or 'average'. Each option progressivly takes more of the image into account for exposure metering. Once started, the exposure will take around 1 second to stabilize, and then continiously auto-expose until disabled, or until Frame is put to sleep |
frame.camera.capture{zoom=1, pan=0, quality=1.0} | Captures a single image from the camera. zoom can be either 1, 2, 3, or 4 returning 720x720, 360x360, 240x240 or 180x180 images respectively. pan can be used to tilt the camera view either up or down. A value of 10 represents the highest viewing angle, 0 is center, and -10 is the lowest. The quality factor can help reduce image size by reducing the JPEG quality. A value of 1.0 represents full quality, and can be reduced to 0.01 for the lowest quality and smallest file size |
frame.camera.read(num_bytes) | Reads out a number of bytes from the camera capture memory as a byte string. Once all bytes have been read, nil will be returned |
Example
local mtu = frame.bluetooth.max_length()
frame.camera.auto(true, 'center_weighted') -- Start auto-mode
frame.sleep(1) -- Wait a little for the exposure to stabilize
frame.camera.capture() -- Capture an image using default settings
while true do
local data = frame.camera.read(mtu)
if data == nil then
break
end
bluetooth.send(data)
end
| Low level functions | Description |
|---|---|
frame.camera.sleep() | Puts the camera to sleep and reduces power consumption. Note the frame.sleep() function will automatically put the camera to sleep |
frame.camera.wake() | Wakes up the camera if it has previously been asleep. Note that following wakeups from frame.sleep() automatically wakes up the camera |
frame.camera.set_exposure(shutter) | Sets the shutter speed in microseconds when camera.auto() is set to false. shutter can be a value between 20 and 20000 |
frame.camera.set_gain(gain) | Sets the analog gain of the sensor when camera.auto() is set to false. gain can be a value between 0 and 255 |
frame.camera.set_white_balance(r, g, b) | Sets the digital gains of the R, G and B channels when camera.auto() is set to false. r, g and b can be values between 0 and 1023 |
frame.camera.set_register(address, value) | Allows for hacking the camera’s internal registers. address can be any 16-bit register address of the camera, and value any 8-bit value to write to that address |
Microphone
The microphone of Frame allows for up to 80kB of recording at a time into a circular buffer. If the recorded data is read out and faster than it is recorded, then the recording can go on continiously. If transfering audio over bluetooth, this limit is around 40kBps under good signal conditions. The audio bitrate for a given sample_rate and bit_depth is: sample_rate * bit_depth / 8 bytes per second.
| API | Description |
|---|---|
frame.microphone.record{seconds=inf, sample_rate=8000, bit_depth=8} | Starts recording for a number of seconds if it is given, otherwise records continiously. sample_rate may be either 20000, 16000, 12500, 10000, 8000, 5000 or 4000. bit_depth maybe either 16, 8, or 4 |
frame.microphone.stop() | Stops any ongoing recording |
frame.microphone.read(num_bytes) | Reads out a number of bytes from the recording buffer. Once all bytes have been read, nil will be returned |
Example
local mtu = frame.bluetooth.max_length()
frame.microphone.record{seconds = 3} -- Record 3 second of audio
frame.sleep(3) -- Wait for the recording to complete and send all the data
while true do
local data = frame.microphone.read(mtu)
if data == nil then
break
end
bluetooth.send(data)
end
Motion sensor (IMU)
The IMU API allows reading both accelerometer and compass data, as well as assigning a callback function for tap gestures.
The tap gesture will always wake up Frame from frame.sleep().
| API | Description |
|---|---|
frame.imu.direction() | Returns a table containing the roll, pitch and heading angles of the wearer’s head position |
frame.imu.tap_callback(handler) | Assigns a callback to the tap gesture. handler must be a function, or can be nil to deactive the callback |
| Low level functions | Description |
|---|---|
frame.imu.raw() | Returns a table of the raw accelerometer and compass measurements. Each containing a table with x, y, and z values |
Example
print(frame.imu.direction()['pitch']) -- Prints the angle of the wears head (up or down)
function tapped() -- Prints 'tapped' whenever the user taps the side of their Frame
print('tapped')
end
frame.imu.tap_callback(tapped)
Bluetooth
The Bluetooth API allows for sending and receiving raw byte data over Bluetooth. For a full description of how this can be used, check out the Bluetooth section of the Building Apps page.
| API | Description |
|---|---|
frame.bluetooth.address() | Returns the device MAC address as a 17 character string. E.g. 4E:87:B5:0C:64:0F |
frame.bluetooth.receive_callback(handler) | Assigns a callback to handle received Bluetooth data. handler must be a function, or can be nil to deactive the callback |
frame.bluetooth.max_length() | Returns the maximum length of data that can be sent or received in a single transfer |
frame.bluetooth.send(data) | Sends data to the host device. data must be a string, but can contain byte values including 0x00 values anywhere in the string. The total length of the string must be less than or equal to frame.bluetooth.max_length() |
Example
function get_data(data) -- Called everytime byte data arrives to Frame
print(data)
end
frame.bluetooth.receive_callback(get_data)
frame.bluetooth.send('\x10\x12\x00\xFF') -- Sends the bytes: 0x10, 0x12, 0x00, 0xFF to the host
File system
The file system API allows for writing and reading files to Frame’s non-volatile storage. These can include executable Lua scripts, or other user files.
| API | Description |
|---|---|
frame.file.open(filename, mode) | Opens a file and returns a file object. filename can be any name, and mode can be either 'read', 'write', or 'append'. |
frame.file.remove(name) | Removes a file or directory of given name |
frame.file.rename(name, new_name) | Renames a file or directory of given name to new_name |
frame.file.listdir(directory) | Lists all files in the directory path given. E.g. '/' for the filesystem root directory. The list is returned as a table with name, size, and type |
frame.file.mkdir(pathname) | Creates a new directory with the given pathname |
f:read(*num_bytes) | Reads a number of bytes from a file. If no argument is give, the whole line is returned |
f:write(data) | Writes data to the file. data must be a string and can contain any byte data |
f:close() | Closes the file. It is important to close files once done writing, otherwise they may become courrupted |
Example
frame.file.mkdir('/my_files') -- Make a new directory
f = frame.file.open('/my_files/log.txt', 'write') -- Create a new file (or overwrite if it exists)
f:write('Log:\n')
f:close()
f = frame.file.open('/my_files/log.txt', 'append') -- Append two lines to the file
f:write('Logged a new line\n')
f:close()
f = frame.file.open('/my_files/log.txt', 'append')
f:write('Logged another line\n')
f:close()
-- Print all the files in the directory
local files = frame.file.listdir('/my_files')
for index, data in ipairs(files) do
print(index)
for key, value in pairs(data) do
print('\t', key, value)
end
end
Time functions
The time functions allow for accurate timekeeping on Frame. The utc() function can be used to set the time on Frame using a UTC timestamp. Frame will then keep the time until it’s put back onto charge, or placed into deep sleep using frame.sleep(). The date() function can be used to return a human readable time and date.
| API | Description |
|---|---|
frame.time.utc(*timestamp) | Sets or gets the current time. timestamp can be provided as a UTC timestamp to set the internal real-time clock. If no argument is given, Frame’s current time is returned as a UTC timestamp. If no timestamp was initially set, this number will simply represent the powered on time of Frame in seconds. |
frame.time.zone(*offset) | Sets or gets the timezone offset. If offset is given, the timezone will be set, otherwise the currently set timezone is returned. The format of the timezone should be a string, e.g. ‘-7:00’, or ‘5:30’. |
frame.time.date(*timestamp) | Returns a table containing second, minute, hour, day, month, year, weekday, day of year, and is daylight saving. If the optional timestamp argument is given, that timestamp will be used to calculate the corresponding date. |
Example
frame.time.utc(1708551112) -- Set the current time to Wed Feb 21 2024 21:31:52 UTC
frame.time.zone('-7:00') -- Set the timezone to pacific time
local time_now = frame.time.date()
-- print the local time and date
print(time_now['hour'])
print(time_now['minute'])
print(time_now['month'])
print(time_now['day'])
System functions
The system API provides miscellaneous functions such as sleep and update. It also contains some low level functions which are handy for developing apps and custom FPGA images.
| API | Description |
|---|---|
frame.FIRMWARE_VERSION | Returns the current firmware version as a 12 character string. E.g. 'v24.046.1546' |
frame.GIT_TAG | Returns the current firmware git tag as a 7 character string. E.g. '4a6ea0b' |
frame.battery_level() | Returns the battery level as a percentage between 1 and 100 |
frame.sleep(*seconds) | Sleeps for a given number of seconds. seconds can be a decimal number such as 1.25. If no argument is given, Frame will go to sleep until a tap gesture wakes it up |
frame.update() | Reboots Frame into the firmware bootloader. Check the firmware updates section of the Building Apps page to see how this is used |
| Low level functions | Description |
|---|---|
frame.stay_awake(enable) | Prevents Frame from going to sleep while it’s docked onto the charging cradle. This can help during development where continious power is needed, however may degrade the display or cause burn-in if used for extended periods of time |
frame.fpga_read(address, num_bytes) | Reads a number of bytes from the FPGA at the given address |
frame.fpga_write(address, data) | Writes data to the FPGA at a given address. data can be a string containing any byte values |