Incorrect I2C port assignments on Adafruit RP2040 Feather

[emeb]

The Adafruit RP2040 Feather board assigns both the SCL/SDA pins on its header and Qwiic connector to RP2040 pins 2,3 which is defined as Wire1 in the file variants/adafruit_feather/pins_arduino.

// Wire
#define PIN_WIRE0_SDA  (24u)
#define PIN_WIRE0_SCL  (25u)
#define PIN_WIRE1_SDA  (2u)
#define PIN_WIRE1_SCL  (3u)

As a result it's necessary to override the default port value in most all interfacing examples which assume Wire/Wire0. This is especially problematic for the miniTFTwing which does not allow overriding the default port in its constructor.

[emeb]

This issue has also been reported to the Adafruit Seesaw library: adafruit/Adafruit_Seesaw#83

[anecdata]

The Feather Specification indicates:

SDA & SCL - this should be your main I2C bus.

(referring to the pins with the "SDA" and SCL" silkscreen, the two at the bottom of the shorter side of feather headers, which correspond in this case to RP2040 pins GP2 and GP3)

Those physical pins on other Feather MCUs are Wire rather than Wire1.

On the Raspberry Pi Pico, GP4 and GP5 are Wire, but they are not available on the Feather RP2040 headers. Other boards in the variants use various pin pairs for Wire (and Wire1, where applicable), also different from the Pico in various ways.

[earlephilhower]

Can you explain what pins should be mapped to Wire and which should go to Wire1? It might be a matter of simply using the swapping capability

arduino-pico/libraries/Wire/src/Wire.cpp

Lines 401 to 409 in 3b4fb29

	#ifndef __WIRE0_DEVICE
	#define __WIRE0_DEVICE i2c0
	#endif
	#ifndef __WIRE1_DEVICE
	#define __WIRE1_DEVICE i2c1
	#endif
	TwoWire Wire(__WIRE0_DEVICE, PIN_WIRE0_SDA, PIN_WIRE0_SCL);
	TwoWire Wire1(__WIRE1_DEVICE, PIN_WIRE1_SDA, PIN_WIRE1_SCL);

[emeb]

These are the pins that are actually connected to I2C functions on the RP2040 Feather:

#define PIN_WIRE1_SDA  (2u)
#define PIN_WIRE1_SCL  (3u)

So those pins ought to actually be WIRE0.

Pins 24 and 25 which are the current defaults (WIRE0) are actually used for SWD programming and only connect to some testpoints and a programming header so they probably shouldn't be assigned to WIRE1. Determining which pins should be WIRE1 is something that's open to discussion.

For reference, see the schematic:
https://cdn-learn.adafruit.com/assets/assets/000/116/896/original/adafruit_products_FeatherRP2040_sch.png

[earlephilhower]

So those pins ought to actually be WIRE0.

Ah, that's just a #define WIRE0 i2c1 and #define WIRE1 i2c0 (and swap the PIN_WIRE_x_XXX) to swap. Basically, right pins but wrong name, yes?

[emeb]

I think so. It seems that you need to change both the WIREX_DEVICE and and PIN_WIRE_ definitions, but that ought to do it.

[caternuson]

The Feather RP2040 variant predates the current BSP's ability to allow I2C pin mapping, which was added here:
#606
So the use of I2C1 ended up being Wire1.

This could be changed, but it would be breaking. All current code using Wire1 would then break.

[emeb]

OK - closing with Do Not Fix.

[earlephilhower]

I think this probably should be fixed, but needs a big notice in release notes. Other Adafruit boards are using the redefined Wire/Wire1 and this is an outlier just because it came early...