Journey's End

Aug 11
2024

PIO and Interrupts

Introduction

I want to be able to raise system level interrupts from PIO programs and there aren’t too many examples of this, so here is my simple contribution.

PIO program

First, the PIO program, which simply waits for a pin to change and then immediately raises PIO IRQ 0.

.program irq_example
.wrap_target

wait 0 pin 0    ; wait for a 0 on IN pin 0
irq nowait 0    ; raise PIO IRQ 0

.wrap

Compile this with pioasm then #include the .h in your C program.

C Program

Interrupt Setup

There are four system level interrupts related to PIO: PIO0_IRQ_0, PIO0_IRQ_1, PIO1_IRQ_0, PIO1_IRQ_1. We shall use PIO0_IRQ_0.

First we attach an interrupt handler to PIO0_IRQ_0:

void isr(void) {
    // clear PIO IRQ 0 that was raised by irq nowait 0
    pio_interrupt_clear(pio0, 0);
}

irq_add_shared_handler(PIO0_IRQ_0,
                       isr,
                       PICO_SHARED_IRQ_HANDLER_DEFAULT_ORDER_PRIORITY);

It is important that pio_interrupt_clear() is called otherwise the CPU will lock up constantly executing the interrupt handler (aka ISR - interrupt service routine)

We then enable the interrupt:

irq_set_enabled(PIO0_IRQ_0, true);

Finally we configure PIO0_IRQ_0 to be triggered when PIO IRQ 0 is raised:

pio_set_irq0_source_enabled(pio0, pis_interrupt0, true);

The functions used above are described in the Pico C SDK documentation.

PIO Setup

The PIO program can now by installed the usual way by first setting up the state machine:

uint sm = pio_claim_unused_sm(pio0, true);
uint offset = pio_add_program(pio0, &irq_example_program);
pio_sm_config cfg = irq_example_program_get_default_config(offset);

Configure and connect GPIO to the state machine:

// connect GP 2 to IN of state machine
sm_config_set_in_pins(&cfg, 2);

// it is an input pin
pio_sm_set_consecutive_pindirs(pio0, sm, 2, 1, false);

// we want pull up on the pin
gpio_pull_up(2);

Now we are ready to start the state machine:

pio_sm_init(pio0, sm, offset, &cfg);
pio_sm_set_enabled(pio0, sm, true);
ts=03:53 tags=[electronics,c,arduino,asm,oss]

Oct 27
2023

DIY EQMod Direct USB Cable

I am in the process of resurrecting my Eq5 Pro so it is compatible with ASIAir Mini. The first step is to build an EQMod Direct USB cable. While it is possible to buy one pre-made, since I had all the parts I decided to build it myself.

Based on …

ts=04:34 tags=[electronics,diy,astronomy]

Sep 17
2023

Build Log: SCD41 CO2 Sensor

CO2 concentration is a proxy for how well a space, especially an enclosed one, is ventillated. To this end I build a quick-n-dirty CO2 sensor using a SCD41 breakout board from pimoroni and bits and pieces I had in the workshop.

Took the opportunity to practice making enclosures, especially for …

ts=14:21 tags=[electronics,arduino,diy,cad,freecad,3dprinting]

Dec 26
2022

Dec 13
2019

How *Not* to Play with Programmable LED Strips

You Need That Resistor

That resistor on the data line? Yeah you need it. Otherwise you might blow an LED which renders the entire rest of the strip useless. If that happens cut out the first LED and solder the power and data lines directly to the second LED.

You …

ts=14:38 tags=[electronics]

Oct 04
2015

May 03
2015

Jul 22
2012

2012-07-22

Over this weekend I have been working on faerii, a USB controlled RGB LED based around the ATtiny85.

Here is a picture of the breadboard prototype

faerii breadboard prototype
The ATtiny85 is mid centre, and immediately above it is the ISP header. To the left of the ISP header, near …
ts=13:09 tags=[software,electronics]

Apr 23
2012

Notes on RF-0417C

Some notes on using the popular Bluetooth serial module RF-0417C:

  • When sending AT commands, do not include \r\n either together or singly.
  • It appears to be happy to receive 5V inputs to TX.
  • It is not happy to receive 5V to Vcc.
  • If you connect a LED, it blinks …
ts=12:13 tags=[electronics,arduino,diy]

Nov 15
2011

May 07
2011

Success for Science

Just finished packaging my engineering thesis project into a more portable format: an altoids tin! I have seen people put some neat stuff inside them, and I am chuffed I managed to as well :) Though I had to cut through the lid for the display. And I only had to …

ts=12:23 tags=[electronics,arduino,diy]

Jun 15
2010

Jun 15
2010

Open Letter to Silicon Chip Australia


Dear Silicon Chip,

I recently cancelled my print subscription. You are no longer a magazine I wish to support.

Political commentary on topics like the insulation scheme and global warming has no place in an electronics magazine. The editor(s) are using the mailbag section to push their own agendas …

ts=06:53 tags=[rant,politics,IRL,electronics]

Dec 31
2009

Dec 21
2009

Jun 03
2009

microbric viper review

The microbric viper is neat. Good quality parts and unique idea. Makes a decent robotics platform if you get the wheel add-on. However, you gotta have small fingers to get some of the parts in place. Despite this, the hardware is solid, I like it. The one thing I would …

ts=14:55 tags=[rant,computer,electronics,arduino,software]

Jun 01
2009

May 29
2009

May 17
2009

Feb 16
2009

Futurlec Ultrasonic Sensor Note

Part number US1440, these sensors are not dual use, which means the transmitter and receiver is not exchangeable. They also look identical from the outside, so if you build my arduino ultrasound ranger with these (as I did) and find you can't see echoes, try swapping your transmitter and receiver …

ts=07:07 tags=[electronics]
Next → Page 1 of 2