This is a demonstration of the use of the Arduino-Pico (Raspberry Pi Pico Arduino core), super-simple, multicore implementation.
The Pico-W will run a WiFi scan on core-0 while simultaneously running a simple LED up/down fader on core-1.
The two cores use an Arduino-Pico provided, multicore-safe FIFO to communicate between themselves.
To use both cores on the RP2040 processor, you only need to know two function calls:-
setup1()loop1()
Yup, if the Arduino-Pico core comes across setup1() function call, it uses the code within that function to initialize core-1 of the processor.
When it finds loop1() it uses the code there as the application code specifically for core-1.
As usual, the normal setup() and loop() function calls are used by core-0, which is the default behaviour for an Arduino application and effectively limits your Pico to being a single core processor.
You should have access to some version of the RP2040 hardware (the Arduino-Pico core supports lots of different third-party boards, as well as the mainstream Pico and Pico-W boards).
You can use this new functionality if you are using the Arduino-Pico (Raspberry Pi Pico Arduino core). I happen to be using it from PlatformIO, but you can just as easily use it directly from the Arduino IDE.
The Arduino-Pico core repository is available on GitHub.
There is also a ton of documentation available, including this installation guide.
The document specific to this, multicore funtionality is here, including details on FIFO usage.
First of all, you need to add your access-point SSID and password at the top of the src/multicore_demo.ino file.
Using whatever system you prefer (PlatformIO, Arduino IDE, etc), compile the code and load it to you Pico/Pico-W board.
- The board will normally reset and run the new firmware on completion of the upload.
- Once the board starts to initialize, the on-board LED will come on for 5-seconds.
- This delay is to allow you time to connect your terminal program (screen, putty, etc) via USB.
- At the end of the 5-second delay, the demo will begin to display start-up messages from core-0.
=== Multicore Demo ===
Core-0: On-Line.
Connecting to AccessPoint1
IP number assigned by DHCP is 192.168.1.10
Core-1: On-Line.
==>> Push BOOTSEL button to trigger WiFi scan.
- Note that core-1 doesn't come on-line at the same time as core-0. We use a delay at the start of
setup1()to ensure that the WiFi can initialize, first.
- The initial start-up messages end with the instruction to push the BOOTSEL button.
The BOOTSEL button is actually monitored by core-1. If you push and release BOOTSEL, the core-1 handler will load a fifo to signal core-0 that it should begin a WiFi network scan.
Core-0 also loads a fifo to notify core-1 that it should run a simple fade-up/fade-down sequence on the on-board LED. So, while core-0 is running the WiFi scan, core-1 is concurrently running the LED fader.
Core-1: Registered button press...
Core-0: Initiating WiFi scan...
Core-1: Received a start-fader command...
Beginning scan at 1630368
Found 3 networks
SSID ENC BSSID CH RSSI
Buffalo-A-6928 AUTO 18:C2:FB:18:D1:16 7 -97
AccessPoint1 WPA2 30:5A:A3:C7:82:10 6 -54
Free_Range_Eggs NONE 68:FF:B7:6A:69:AB 1 -88
---
At this point everything goes back to waiting for further BOOTSEL events.
I have to admit that I don't have a non-WiFi Pico model, so I don't know how well (or badly) one will react to the request for a WiFi scan. If it all falls over in a heap, then you can probably just completely remove the WiFi.h include and replace the WiFi scan with a simple message from core-0 instead.
You will notice that the src directory has a pwm.ino file, in addition to the multicore_demo.ino. This was prompted by the fact that the on-board LED on the Pico-W is not attached to an RP2040 GPIO pin, but to one of the wireless module's pins. This means that it doesn't have PWM functionality and the normal analogWrite() call cannot be used. The (crude) code in pwm.ino is just a very simple up/down fader using nothing more than on/off writes to the pin with some very short delays between them. The calls to delay() are, of course, blocking, but as this is running solely on core-1, it does not impact the WiFi scan process, which runs concurrently on core-0.
If nothing else, this does provide a real-life genuine example of the multitasking capability of the RP2040 (and yes, I know it's still a really crappy fader!).
The pwm.ino code should work fine with an older, non-WiFi Pico, but if you have one of those boards and want to experiment, it is trivial to import the Arduino-Pico/libraries/rp2040/examples/Fade/Fade.ino example code into the multicore_demo.ino file and delete the extra pwm.ino code completely. Obviously the resulting firmware will not work with a Pico-W if you make this change.
The Arduino-Pico repository is owned and maintained by Earle F. Philhower (with additional contributors). Earle added the setup1() & loop1() functionality on the 25th of April 2021 -- see pull request #113. So we owe Earle a debt of gratitude not just for easy multicore, but also for the Arduino-Pico core itself. Let's hope that we see other people picking up this neat idea and that we see the spread of setup1()/loop1() to other Arduino cores soon.