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librasp

Raspberry Pi library for GPIO, 1-Wire, SPI, System Time Counter (STC) access. As an example of usage there have been provided APIs for handling various popular devices like wireless nRF24L01 transceiver, DHT temperature sensors (DHT11/22), Dallas family of temperature sensors (e.g. DS18B20, DS1822, DS1825), HC-SR04 distance sensor, PISO shift register...

API specification contained in the library headers (see src/inc/librasp). For examples look in examples.

NOTE: 1-wire and SPI API bases on generic Linux interfaces (ioctl(2), netlink(3)) and doesn't relay on any RPi platform specific details. For this reason the 1-wire and SPI services may be used on any embedded Linux platform (e.g. dsth_list and dsth_list2 examples may be used to read-out connected Dallas sensors).

Compilation

make

produces static library src/librasp.a which may be linked into an application.

make examples

will compile examples.

There is possible to cross-compile the library by setting CROSS_COMPILE (for the project Makefile) to the tool-chain prefix:

CROSS_COMPILE=<tool-chain-prefix> make

1-wire and parasite powering

The original Linux kernel 1-wire driver (the wire module) doesn't provide proper interface for parasite powering of 1-wire slaves via userland's netlink protocol.

  1. To handle this issue there has been provided a patch for the kernel allowing the library to fully support the parasite mode. Look in src/kernel directory for more info.

  2. Configure the library with CONFIG_WRITE_PULLUP parameter while building the library (see src/config.h header for details).

  3. RPi uses w1-gpio module as a 1-wire bus master driver. The driver needs to be configured to support bit-banged strong pull-up on the data wire, required for parasite powering of the connected slaves. Add the following line in /boot/config.txt to turn it on via the device-tree overlay (reboot is required):

    dtoverlay=w1-gpio,pullup=on

    NOTE: This step is not required when using w1-gpio-cl driver instead of w1-gpio.

    To reach for the full power of the library, it is strongly recommended to use the w1-gpio-cl driver instead of the standard one. The primary benefit is support for more than one bus master simultaneously and much more mature parasite powering handling. See the above link for more details.

Refer examples/dsth_list* samples for details on probing the parasite powered Dallas family of temperature sensors.

License

2 clause BSD license. See LICENSE file for details.