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| pigpio pigpio C I/F pigpiod pigpiod C I/F Python pigs piscope Misc Examples Download FAQ Site Map | Frequently Asked QuestionsAudio is broken Can´t initialise pigpio library Can´t lock var/run/pigpio.pid Hello World! Clock skew, make fails Have I fried my GPIO? How do I debounce inputs? How fast is SPI? Library update didn't work make fails with clock skew Porting pigpio to another CPU/SoC Sound isn't working Symbol not found What is I2C? What is Serial? What is SPI? Which library should I use? Are my GPIO broken?Audio is brokenCan´t lock /var/run/pigpio.pidSee Can´t_initialise_pigpio_library Can´t initialise pigpio libraryThis message means the pigpio daemon is already running. The default daemon is called pigpiod and may be removed as
follows.
Kill the daemon with
If your own program is acting as the daemon it may be removed as follows. Find its process id (pid).
Kill the program with
To start the daemon do
Have I fried my GPIO?If you think you have damaged one or more GPIO you can carry out a diagnostic test. The test is a command line script called gpiotest For the duration of the test nothing must be connected to the GPIO (no LEDs, wires, ribbon cables etc.).The test checks that each GPIO may be read and written and that the internal resistor pull-ups and pull-downs are functional. A video showing what happens to the GPIO during a test. A test with all GPIO okay. This program checks the Pi's (user) gpios. The program reads and writes all the gpios. Make sure NOTHING is connected to the gpios during this test. The program uses the pigpio daemon which must be running. To start the daemon use the command sudo pigpiod. Press the ENTER key to continue or ctrl-C to abort... Testing... Skipped non-user gpios: 0 1 28 29 30 31 Tested user gpios: 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 A test showing failed GPIO. This program checks the Pi's (user) gpios. The program reads and writes all the gpios. Make sure NOTHING is connected to the gpios during this test. The program uses the pigpio daemon which must be running. To start the daemon use the command sudo pigpiod. Press the ENTER key to continue or ctrl-C to abort... Testing... Write 1 to gpio 17 failed. Pull up on gpio 17 failed. Write 1 to gpio 18 failed. Pull up on gpio 18 failed. Write 0 to gpio 23 failed. Pull down on gpio 23 failed. Write 0 to gpio 24 failed. Pull down on gpio 24 failed. Write 1 to gpio 27 failed. Pull up on gpio 27 failed. Skipped non-user gpios: 0 1 28 29 30 31 Tested user gpios: 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 How do I debounce inputs?Some devices like mechanical switches can generate multiple
interrupts as they bounce between on and off. It is possible
to debounce the inputs in hardware by the correct use of resistors
and capacitors. In software use the glitch filter which ignores all events
shorter than a set number of microseconds. C gpioGlitchFilter, Python set_glitch_filter. How fast is SPI?The SPI throughput in samples per second depends on a number of factors.
Two of those factors are fixed, the variable is the driver used. The pigpio driver is considerably faster than the Linux SPI
driver as is demonstrated by the following graphs. Each graph shows the SPI bit rate in bits per second along the
horizontal axis. The samples per second achieved is shown on
the vertical axis. Each graph contains plots assuming 1 to 5
bytes per transfer. The source code used for the tests is spi-driver-speed.c and spi-pigpio-speed.c
Library update didn't workpigpio places files in the following locations /usr/local/include (pigpio.h, pigpiod_if.h, pigpiod_if2.h) /usr/include (pigpio.h, pigpiod_if.h, pigpiod_if2.h) Mostly this doesn't matter as the /usr/local directories will
generally be earlier in the search path. The pigpio built
includes, binaries, and manuals are normally found first. However the wrong libraries may be linked during the compilation. If this is the case remove the /usr/lib entries for libpigpio.so , libpigpiod_if.so, and libpigpiod_if2.so Hello World!The following examples show how to use the various components of the pigpio library. Each example shows how to read the level of a GPIO. Cread_cif.c
#include <stdio.h>
#include <pigpio.h>
int main(int argc, char *argv[])
{
int GPIO=4;
int level;
if (gpioInitialise() < 0) return 1;
level = gpioRead(GPIO);
printf("GPIO %d is %d\n", GPIO, level);
gpioTerminate();
}
Build gcc -pthread -o read_cif read_cif.c -lpigpio
Run sudo ./read_cif
C via pigpio daemonread_pdif.c
#include <stdio.h>
#include <pigpiod_if2.h>
int main(int argc, char *argv[])
{
int pi;
int GPIO=4;
int level;
pi = pigpio_start(0, 0); /* Connect to local Pi. */
if (pi < 0)
{
printf("Can't connect to pigpio daemon\n");
return 1;
}
level = gpio_read(pi, GPIO);
printf("GPIO %d is %d\n", GPIO, level);
pigpio_stop(pi); /* Disconnect from local Pi. */
return 0;
}
Build gcc -pthread -o read_pdif read_pdif.c -lpigpiod_if2
Run ./read_pdif
Pythonread_gpio.py
#!/usr/bin/env python
import pigpio
GPIO=4
pi = pigpio.pi()
if not pi.connected:
exit()
level = pi.read(GPIO)
print("GPIO {} is {}".format(GPIO, level))
pi.stop()
Run python read_gpio.py
pigs
pigs r 4
pipe I/F
echo "r 4" >/dev/pigpio
cat /dev/pigout
make fails with clock skewIf make fails with one of the following messages it is probably
because the Pi's clock is wrong.
make uses the current time to work out which files need to be
rebuilt (a file is rebuilt if it depends on other files which have
a later time-stamp). The solution is to make sure the system clock is correct.
If the Pi is networked this will not normally be a problem. To set the date and time use the date command as in the following example.
Porting pigpio to another CPU/SoCSound isn't workingThe Pi contains two pieces of hardware, a PWM peripheral and a
PCM peripheral, to generate sound. The PWM peripheral is
normally used and generates medium quality audio out of the
headphone jack. The PCM peripheral may be used by add-ons
such as HATs and generates high quality audio. pigpio uses at least one of these peripherals during normal
operation (for timing DMA transfers). pigpio will use both
peripherals if waves or the hardware PWM function is used. By default pigpio uses the PCM peripheral leaving the PWM
peripheral free for medium quality audio. You can change the default with a configuration option. For C use gpioCfgClock, for the pigpio daemon use the -t option. What is I2C?I2C is a data link between the Pi (master) and one or more slaves. Data may be sent and received but the Pi initiates all
transfers. I2C is a medium speed link. On the Pi the default speed is
100 kbps, but 400 kbps also works. I2C is implemented as a bus with two lines called
Only one slave device may be communicated with at a time. Each message from the Pi includes the slave to be addressed and whether a read or write is to be performed. When the Pi (master) wishes to talk to a slave it begins by issuing a start sequence on the I2C bus. A start sequence is one of two special sequences defined for the I2C bus, the other being the stop sequence. The start sequence and stop sequence are special in that these are the only places where the SDA (data line) is allowed to change while the SCL (clock line) is high. When data is being transferred, SDA must remain stable and not change whilst SCL is high. The start and stop sequences mark the beginning and end of a transaction with the slave device.  Data is transferred in 8-bit bytes. The bytes are placed on the SDA line starting with the most significant bit. The SCL line is then pulsed high, then low. For every byte transferred, the device receiving the data sends back an acknowledge bit, so there are actually 9 SCL clock pulses to transfer each 8-bit byte of data. If the receiving device sends back a low ACK bit, then it has received the data and is ready to accept another byte. If it sends back a high then it is indicating it cannot accept any further data and the master should terminate the transfer by sending a stop sequence.
What is Serial?Serial is a data link between the Pi and one other
device. Data may be sent and received. Either the Pi or the device
can initiate a transfer. Serial is a low to medium speed link. On the Pi speeds of
50, 75, 110, 134, 150, 200, 300, 600, 1200, 1800, 2400, 4800, 9600,
19200, 38400, 57600, 115200, and 230400 bps may be used. Serial is implemented with one line for transmit called TXD and
one line for receive called RXD. If only receive or transmit are required the other line need not
be connected. The Pi uses GPIO 14 (pin 8) for TXD and GPIO 15 (pin 10) for
RXD. Data is normally transmitted in 8-bit bytes with a start bit,
eight data bits, no parity, and one stop bit. This is
represented as 8N1. The number of transmitted bits per second
(bps) is called the baud rate. The time for each bit,
1 / baud rate seconds, is
referred to as the bit period. The lines are in the high state when no data is being
transmitted. The start of a byte is signalled by the line
going low for one bit period (the start bit). The data bits
are then sent least significant bit firsts (low if the bit is 0,
high if the bit is 1). The data bits are followed by the
optional parity bit. Finally the line is set high for at
least the number of stop bit periods. The line will stay high
if there are no more bytes to be transmitted.
What is SPI?SPI is a data link between the Pi (master) and one or more slaves. Data may be sent and received but the Pi initiates all
transfers. SPI is a medium to high speed link. On the Pi speeds of 32
kbps to 8 Mbps may be used. SPI is implemented as a bus with three lines called
The Pi has two SPI buses
Which library should I use? |
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Updated: 01/01/2023 |