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lua-periphery 
Linux Peripheral I/O (GPIO, LED, PWM, SPI, I2C, MMIO, Serial) with Lua
lua-periphery is a library for GPIO, LED, PWM, SPI, I2C, MMIO, and Serial peripheral I/O interface access in userspace Linux. It is useful in embedded Linux environments (including Raspberry Pi, BeagleBone, etc. platforms) for interfacing with external peripherals. lua-periphery is compatible with Lua 5.1 (including LuaJIT), Lua 5.2, Lua 5.3, and Lua 5.4, has no dependencies outside the standard C library and Linux, is portable across architectures, and is MIT licensed.
Using Python or C? Check out the python-periphery and c-periphery projects.
Contributed libraries: java-periphery, dart_periphery
Examples
GPIO
local GPIO = require('periphery').GPIO
-- Open GPIO /dev/gpiochip0 line 10 with input direction
local gpio_in = GPIO("/dev/gpiochip0", 10, "in")
-- Open GPIO /dev/gpiochip0 line 12 with output direction
local gpio_out = GPIO("/dev/gpiochip0", 12, "out")
local value = gpio_in:read()
gpio_out:write(not value)
gpio_in:close()
gpio_out:close()
LED
local LED = require('periphery').LED
-- Open LED led0
local led = LED("led0")
-- Turn on LED (set max brightness)
led:write(true)
-- Set half brightness
led:write(math.floor(led.max_brightness / 2))
-- Turn off LED (set zero brightness)
led:write(false)
led:close()
PWM
local PWM = require('periphery').PWM
-- Open PWM chip 0, channel 10
local pwm = PWM(0, 10)
-- Set frequency to 1 kHz
pwm.frequency = 1e3
-- Set duty cycle to 75%
pwm.duty_cycle = 0.75
-- Enable PWM output
pwm:enable()
pwm:close()
SPI
local SPI = require('periphery').SPI
-- Open spidev1.0 with mode 0 and max speed 1MHz
local spi = SPI("/dev/spidev1.0", 0, 1e6)
local data_out = {0xaa, 0xbb, 0xcc, 0xdd}
local data_in = spi:transfer(data_out)
print(string.format("shifted out {0x%02x, 0x%02x, 0x%02x, 0x%02x}", unpack(data_out)))
print(string.format("shifted in {0x%02x, 0x%02x, 0x%02x, 0x%02x}", unpack(data_in)))
spi:close()
I2C
local I2C = require('periphery').I2C
-- Open i2c-0 controller
local i2c = I2C("/dev/i2c-0")
-- Read byte at address 0x100 of EEPROM at 0x50
local msgs = { {0x01, 0x00}, {0x00, flags = I2C.I2C_M_RD} }
i2c:transfer(0x50, msgs)
print(string.format("0x100: 0x%02x", msgs[2][1]))
i2c:close()
MMIO
local MMIO = require('periphery').MMIO
-- Open am335x real-time clock subsystem page
local rtc_mmio = MMIO(0x44E3E000, 0x1000)
-- Read current time
local rtc_secs = rtc_mmio:read32(0x00)
local rtc_mins = rtc_mmio:read32(0x04)
local rtc_hrs = rtc_mmio:read32(0x08)
print(string.format("hours: %02x minutes: %02x seconds: %02x", rtc_hrs, rtc_mins, rtc_secs))
rtc_mmio:close()
-- Open am335x control module page
local ctrl_mmio = MMIO(0x44E10000, 0x1000)
-- Read MAC address
local mac_id0_lo = ctrl_mmio:read32(0x630)
local mac_id0_hi = ctrl_mmio:read32(0x634)
print(string.format("MAC address: %04x%08x", mac_id0_lo, mac_id0_hi))
ctrl_mmio:close()
Serial
local Serial = require('periphery').Serial
-- Open /dev/ttyUSB0 with baudrate 115200, and defaults of 8N1, no flow control
local serial = Serial("/dev/ttyUSB0", 115200)
serial:write("Hello World!")
-- Read up to 128 bytes with 500ms timeout
local buf = serial:read(128, 500)
print(string.format("read %d bytes: _%s_", #buf, buf))
serial:close()
Error Handling
lua-periphery errors are descriptive table objects with an error code string, C errno, and a user message.
-- Example of error caught with pcall()
> status, err = pcall(function () spi = periphery.SPI("/dev/spidev1.0", 0, 1e6) end)
> =status
false
> dump(err)
{
message = "Opening SPI device \"/dev/spidev1.0\": Permission denied [errno 13]",
c_errno = 13,
code = "SPI_ERROR_OPEN"
}
>
-- Example of error propagated to user
> periphery = require('periphery')
> spi = periphery.SPI('/dev/spidev1.0', 0, 1e6)
Opening SPI device "/dev/spidev1.0": Permission denied [errno 13]
>
Note about Lua 5.1
Lua 5.1 does not automatically render the string representation of error objects that are reported to the console, and instead shows the following error message:
> periphery = require('periphery')
> gpio = periphery.GPIO(14, 'in')
(error object is not a string)
>
These errors can be caught with pcall() and rendered in their string
representation with tostring(), print(), or by evaluation in the
interactive console:
> periphery = require('periphery')
> gpio, err = pcall(periphery.GPIO, 14, 'in')
> =tostring(err)
Opening GPIO: opening 'export': Permission denied [errno 13]
> print(err)
Opening GPIO: opening 'export': Permission denied [errno 13]
> =err
Opening GPIO: opening 'export': Permission denied [errno 13]
>
This only applies to Lua 5.1. LuaJIT and Lua 5.2 onwards automatically render the string representation of error objects that are reported to the console.
Documentation
man page style documentation for each interface is available in docs folder.
Installation
Build and install with LuaRocks
$ sudo luarocks install lua-periphery
Build and install from source
Clone lua-periphery recursively to also fetch c-periphery, which lua-periphery is built on.
$ git clone --recursive https://github.com/vsergeev/lua-periphery.git
$ cd lua-periphery
$ make clean all
$ cp periphery.so /path/to/lua/libs/
Place periphery.so in a directory searched by the Lua package.cpath variable. For example: /usr/lib/lua/5.3/, the same directory as other Lua sources, etc.
lua-periphery can then be loaded in lua with periphery = require('periphery').
Cross-compiling from Source
Set the CROSS_COMPILE environment variable with the cross-compiler prefix when calling make. Your target's sysroot must provide the Lua includes.
$ CROSS=arm-linux- make clean all
cd c-periphery && make clean
make[1]: Entering directory '/home/anteater/projects/software/lua-periphery/c-periphery'
rm -rf periphery.a obj tests/test_serial tests/test_i2c tests/test_gpio_sysfs tests/test_mmio tests/test_spi tests/test_gpio
make[1]: Leaving directory '/home/anteater/projects/software/lua-periphery/c-periphery'
rm -rf periphery.so
cd c-periphery; make
make[1]: Entering directory '/home/anteater/projects/software/lua-periphery/c-periphery'
mkdir obj
arm-linux-gcc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter -fPIC -DPERIPHERY_VERSION_COMMIT=\"v2.0.1\" -c src/gpio.c -o obj/gpio.o
arm-linux-gcc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter -fPIC -DPERIPHERY_VERSION_COMMIT=\"v2.0.1\" -c src/spi.c -o obj/spi.o
arm-linux-gcc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter -fPIC -DPERIPHERY_VERSION_COMMIT=\"v2.0.1\" -c src/i2c.c -o obj/i2c.o
arm-linux-gcc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter -fPIC -DPERIPHERY_VERSION_COMMIT=\"v2.0.1\" -c src/mmio.c -o obj/mmio.o
arm-linux-gcc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter -fPIC -DPERIPHERY_VERSION_COMMIT=\"v2.0.1\" -c src/serial.c -o obj/serial.o
arm-linux-gcc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter -fPIC -DPERIPHERY_VERSION_COMMIT=\"v2.0.1\" -c src/version.c -o obj/version.o
arm-linux-ar rcs periphery.a obj/gpio.o obj/spi.o obj/i2c.o obj/mmio.o obj/serial.o obj/version.o
make[1]: Leaving directory '/home/anteater/projects/software/lua-periphery/c-periphery'
arm-linux-gcc -std=c99 -pedantic -D_XOPEN_SOURCE=700 -Wall -Wextra -Wno-unused-parameter -fPIC -I. -Iinc -shared src/lua_periphery.c src/lua_mmio.c src/lua_
gpio.c src/lua_spi.c src/lua_i2c.c src/lua_serial.c c-periphery/periphery.a -o periphery.so
$ file periphery.so
periphery.so: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, not stripped
$
Testing
The tests located in the tests folder may be run under Lua to test the correctness and functionality of lua-periphery. Some tests require interactive probing (e.g. with an oscilloscope), the installation of a physical loopback, or the existence of a particular device on a bus. See the usage of each test for more details on the required setup.
License
lua-periphery is MIT licensed. See the included LICENSE file.