JSON platform loading allows libmraa users who work with simple and unsupported boards to create JSON configuration files which libmraa understands, allowing libmraa to just 'work' with the unsupported platform. JSON platform does not work with boards which require advanced functions which overwrite default functionality or boards that require the mux functionality.

Syntax

The JSON file that libmraa reads needs specific values to be set by default, they are required in every JSON file intended to be used to load the platform. The keywords are case sensitive so be aware when writing the JSON file. Each heading is a top level key in the JSON file, each key's type is Array

platform

Key	Type	Required	Description
id	int	no	An ID that can be assigned
name	string	yes	The platform name
pin_count	int	yes	The total pin count
gpio_count	int	no	The subset of pincount which able to do GPIO
i2c_count	int	no	The number of usable I2C ports
aio_count	int	no	The number of usable AIO ports
spi_count	int	no	The number of usable SPI ports
uart_count	int	no	The total UART ports
pwmDefPeriod	int	no	The default PWM period
pwmMaxPeriod	int	no	The max PWM period
pwmMinPeriod	int	no	The min PWM period

layout

THIS INDEX'S THE PIN ARRAY Each available pin specified using pin_count requires a label. There is no need to use an index identifier as the json objects are indexed as they are read, starting with the first json object being treated as index 0.

The number of json objects in layout should be equal to the pin_count.

Key	Type	Required	Description
label	string	yes	The label used to describe the pin (11 characters max)
invalid	boolean	no	Sets the labeled pin as an invalid pin

GPIO

THIS INDEX'S THE PIN ARRAY For the supported GPIO pins here is where we set the raw linux pin it needs to use, the index cannot exceed the total pin_count and the number of JSON ojects cannot exceed the gpio_count total. The index is also used to set the specified pin's capabilities. Each set of keys should be enclosed in a json object.

Key	Type	Required	Description
index	int	yes	used to index the pin array
rawpin	int	yes	used to reference the actual IO pin

I2C

THIS INDEX'S THE I2C ARRAY This is used to setup the I2C functionality. The total number of json objects and the index cannot exceed the i2c_count. Each set of keys should be enclosed in a json object.

Key	Type	Required	Description
index	int	yes	Used to index the I2C array
rawpin	int	yes	The sysfs pin
sclpin	int	no	The clock pin
sdapin	int	no	The data pin
default	boolean	no	Sets the default I2C device used

AIO

THIS INDEX'S THE PIN ARRAY This is used to setup which pins are able to perform AIO. Each set of keys should be enclosed in a json object.

Key	Type	Required	Description
index	int	yes	Used to index the pin array
rawpin	int	yes	The sysfs pin

PWM

THIS INDEX'S THE PIN ARRAY This is used to setup which IO pins can do PWM Each set of keys should be enclosed in a json object.

Key	Type	Required	Description
index	int	yes	Used to index the pin array
rawpin	int	yes	The sysfs pin
chipID	int	yes	The parent ID

SPI

THIS INDEX'S THE SPI ARRAY This is used to setup the SPI functionality. The total number of json objects and the index cannot exceed the spi_count. Each set of keys should be enclosed in a json object.

Key	Type	Required	Description
index	int	yes	The index into the SPI array
chipID	int	yes	The parent ID
clock	int	no	The clock used for transmissions
miso	int	no	Pin used for incoming data from the slave
mosi	int	no	Pin used for outgoing data from the master
chipselect	int	no	Pin used to select the slave device
default	boolean	no	Sets the default SPI device

UART

THIS INDEX'S THE UART ARRAY This is used to setup the UART functionality. The total number of json objects and the index cannot exceed the uart_count. Each set of keys should be enclosed in a json object.

Key	Type	Required	Description
index	int	yes	Used to index the UART array
chipID	int	yes	Parent ID
rawpin	int	yes	Sysfs pin
rx	int	no	Read pin
tx	int	no	Transmit pin
path	string	yes	Used to talk to a connected UART device
default	boolean	no	Sets the default UART device