mraa  1.7.0
Low Level Skeleton Library for Communication on GNU/Linux platforms
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JSON platform

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 booleanno 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 booleanno 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 booleanno 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 booleanno Sets the default UART device