Raspberry Pico SPI and I2C pins

[sstaub]

Raspberry Pico
How to determine which pins are used for SPI, and how to do this for SPI1. Are there any standard pins?
Same for I2C. Is there any API (with examples)?

[Grumpy-Mike]

Pico-R3-A4-Pinout.pdf
You can use any of these pins for I2C, note there are two I2C buses as well. You have to tell the Pico what pins you are going to use when you initialise it.

[sstaub]

I know about the pins I can use. But how to configure?

[Grumpy-Mike]

This is an example of using the I2C to drive an LCD

lcd_1602_i2c.c.zip

[sstaub]

@Grumpy-Mike What have the code todo with ArduinoCore-Core?

[Grumpy-Mike]

Don't understand the question sorry.

[stuartdd]

This is my understanding | miss-understanding.

I have been using the code from earlephilhower/arduino-pico with some success.
My SSD1306 plays Space Invaders, nice!

I wanted to use the official Arduino release and followed the link to this repo.

Initial Process (Not using README.md):

1. I downloaded a fresh Arduino IDE, Removed all Arduino related libs from my user and started the IDE.
2. I went to the Board Manager an installed 'Arduino OS RP2040 Boards'.
3. I selected the 'Raspberry PI Pico' board.
4. I uploaded the Blink sketch pressed upload (which failed)
5. I Ran the post-install.sh (from your repo) as root. This fixed the above issue!
6. I uploaded the sketch and the LED started to blink. YAHAOO!
   Does this use the code from ArduinoCore-mbed?
   If NOT what is the difference between ArduinoCore-mbed and the IDE's Board installation?
7. I loaded up a sketch that uses the I2C interface to drive a OLED display using 'Adafruit_SSD1306.h' library.
8. I cannot find a way of defining the SDA and SCL pins used by the Wire api.
9. I looked at lcd_1602_i2c.c.zip and it says:
   GPIO 4 (pin 6)-> SDA on LCD bridge board
   GPIO 5 (pin 7)-> SCL on LCD bridge board
   This does NOT work and is not an Arduino sketch (very confusing).

There is no data being sent to the display. I tried GP0/GP1, GP4/GP5, GP12/GP13, GP17/GP16, GP21/GP20 no luck on any.

How do I define (within a Sketch) the Pico pins used by the Wire API for SCL and SDA?

Second Process:

1. I started from scratch (Removed all Arduino related libs from my user and started the IDE) as above.

2. I followed the README.md on this repo.
   This installs mbed and ArduinoCore-API libraries.
   It assumed I knew what $sketchbook was, I did not.
   There was no 'symlink to api'. I created one.
   The IDE failed to load as it could not find boards.txt.
   I moved some directories around and finally got the IDE running.

   I could NOT see the Pico boards. I only had the original boards as selected in my initial process!

I gave up and went back to using earlephilhower/arduino-pico

So Three questions I have!

1. What is the difference between ArduinoCore-mbed and the IDE's existing Board Manager Pico installation
2. How do I define (within a Sketch) the Pico pins used by the Wire API for SCL and SDA?
3. Which should I use? ArduinoCore-API libraries (Arduino-core) or the IDE board manager?

I have to say that I am VERY excited about using Arduino code for my Pico. I do not wish to seem critical but at the moment this is not usable without help from the developers.

That earlephilhower/arduino-pico API adds setSCL(n) and setSDA(n) to the Wire API and it just works.

Please help me understand the above issues.

Regards

Stuart

[sstaub]

The code of earlephilhower/arduino-pico is based on c++ sdk of Arduino. This core is based on Mbed.
Meanwhile I found out that the SPI / I2C pins doesn't follow the official pinup of raspberry pi pico.
I'm missing an API for changing the pins like pinSwap on other cores. I need to try the underlined Mbed core the next days.
In pins_arduino.h there are some basic pins for SPI and I2C but not for SPI1 and WRE1 also for UART, so I think some rework is needed.

[TobiasVanDyk]

My SSD1306 plays Space Invaders, nice!

7. I loaded up a sketch that uses the I2C interface to drive a OLED display using 'Adafruit_SSD1306.h' library.

   GPIO 4 (pin 6)-> SDA on LCD bridge board
   GPIO 5 (pin 7)-> SCL on LCD bridge board
   This does NOT work and is not an Arduino sketch (very confusing).

Stuart

Hi Stuart
I also used an SD1306 i2c OLED with BOTH mbed and the C++SDK Arduino libraries
For the mbed I copy this part from my github: an existing Arduino IDE 1.8.13 installation was used with the Arduino mbed-based installation and two Adafruit graphics libraries were installed as described. Connect the OLED display SDA to Pico pin 9 (GP6) and SCL to Pico pin 10 (GP7). This was based on the discussion here - the Arduino-mbed-Pico board uses a fixed i2c-1 assignment for SDA and SCL. The Adafruit example used, had its i2c address changed from 0x3D to 0x3C for this particular OLED display - the modified sketch is inside the OLEDArduino folder above as ssd1306_128x64_i2cPico.ino.

It is working with the mbed Arduino and Adafruit graphics libs

[sstaub]

The official hardware documentation says following.
I2C
GP4 SDA
GP5 SCL

SPI0
GP16 SS
GP17 MISO
GP18 SCK
GP19 MOSI

I think the board definition should follow the official docs as a reference.
SDA on GP6 and SCL on GP7 is I2C 1 not 0 as expected
MISO is GP4, MOSI GP3, SCK is GP2, SS is GP5
this should changed to the pins above.

There is a need a function to set alternative pins for UART, SPI, I2C
On Mbed you do it when declaring a class like MbedI2C I2C(GP6, GP7);
The DX core https://github.com/SpenceKonde/DxCore have this functionality

[sstaub]

I forgot, we need some standard pins for I2C 1, SPI 1 and UART 1

[facchinm]

Hi everyone,
first of all, sorry for the lack of documentation, we are working hard to fix it.
On the Pico, pins are not marked as per theirs hardware function, so we decided to create two default objects (SPI and Wire hooked to pins 2,3,4,5 and 6,7 https://github.com/arduino/ArduinoCore-mbed/blob/master/variants/RASPBERRY_PI_PICO/pins_arduino.h#L44-L57 ). The hardware peripheral they are connected with is not active until you call begin(), so it can be safely overridden if you need to use another set of pins.
The easiest way is to create objects (as @sstaub reported) with the pins you want to use.
For example, if you need an I2C on GP14/GP15 just create an object this way

MbedI2C myi2c(p14,p15);

Keep in mind that selecting the wrong pins (if the mux is not possible) will raise a runtime error (with the usual "morse-like" led blink).
For additional compatibility we are going to push 1162086 on the next revision, so the objects can be created either by using the pin name or their number (not so useful on the Pico since names match numbers but convenient on other boards).

[sstaub]

The hardware docs of pico the default pins are marked, see screenshot from the doc.

@facchinm can you add default pins for SERIAL2 (Uart2), SPI1 and WIRE1 ?
Also a '::pins()' function will helpful for SERIAL, SPI and WIRE like 'Serial1.pins(TX pin, RX pin)'
This functionality avoids digging in the Mbed API.

[facchinm]

@sstaub as marked I meant the silkscreen on the board itself, which we always considered the "golden standard" for naming.
About pins() API, it's not standard as per https://github.com/arduino/ArduinoCore-API/tree/master/api , so we are not going to add it anytime soon.
I think the way to go is to properly document how to create Serial2, Wire1 or SPI1 objects in the user sketch (or in a library) with the correct constructor (as we did to add additional SERCOM to SAMD core https://www.arduino.cc/en/Tutorial/SamdSercom).
@sebromero @alranel what do you think?

[sstaub]

The constructors for Wire1 and SPI1In Wire Wire.cpp and SPI.cpp are already done, only the pins definitions in pins_arduino.h are missing, same for Serial.