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Add I2C support to RP2 platform
Signed-off-by: Paul Guyot <pguyot@kallisys.net>
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‎examples/erlang/rp2/CMakeLists.txt‎

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@@ -24,6 +24,8 @@ include(BuildErlang)
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pack_uf2(hello_pico hello_pico)
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pack_uf2(pico_blink pico_blink)
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pack_uf2(pico_i2c_scanner pico_i2c_scanner)
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pack_uf2(pico_lis3dh pico_lis3dh)
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pack_uf2(pico_rtc pico_rtc)
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pack_uf2(picow_blink picow_blink)
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pack_uf2(picow_wifi_sta picow_wifi_sta)

‎examples/erlang/rp2/pico_i2c_scanner.erl‎

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%
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% This file is part of AtomVM.
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%
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% Copyright 2026 Paul Guyot <pguyot@kallisys.net>
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%
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% Licensed under the Apache License, Version 2.0 (the "License");
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% you may not use this file except in compliance with the License.
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% You may obtain a copy of the License at
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%
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% http://www.apache.org/licenses/LICENSE-2.0
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%
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% Unless required by applicable law or agreed to in writing, software
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% distributed under the License is distributed on an "AS IS" BASIS,
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% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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% See the License for the specific language governing permissions and
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% limitations under the License.
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%
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% SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
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%
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%%-----------------------------------------------------------------------------
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%% @doc I2C bus scanner example for Pico.
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%%
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%% Scans all valid 7-bit I2C addresses (0x08-0x77) and prints which devices
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%% respond with an ACK.
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%%
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%% Default wiring (Pico pin numbers):
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%% SDA -> GP4 (pin 6)
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%% SCL -> GP5 (pin 7)
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%% GND -> pin 8
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%% 3V3 -> pin 36
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%%
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%% These are the default I2C0 pins on the Pico.
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%% @end
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%%-----------------------------------------------------------------------------
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-module(pico_i2c_scanner).
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-export([start/0]).
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%% I2C pins (I2C0 default on Pico)
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-define(SDA_PIN, 4).
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-define(SCL_PIN, 5).
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start() ->
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I2C = i2c:open([
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{scl, ?SCL_PIN},
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{sda, ?SDA_PIN},
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{clock_speed_hz, 100000},
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{peripheral, 0}
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]),
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console:puts("I2C bus scan (0x08-0x77):\n"),
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Found = scan(I2C, 16#08, []),
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case Found of
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[] ->
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console:puts("No devices found.\n");
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_ ->
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console:puts("Done. Found "),
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console:puts(erlang:integer_to_list(length(Found))),
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console:puts(" device(s).\n")
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end.
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scan(_I2C, Addr, Acc) when Addr > 16#77 ->
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lists:reverse(Acc);
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scan(I2C, Addr, Acc) ->
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NewAcc =
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case i2c:read_bytes(I2C, Addr, 1) of
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{ok, _} ->
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console:puts(" 0x"),
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console:puts(erlang:integer_to_list(Addr, 16)),
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console:puts(" ACK\n"),
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[Addr | Acc];
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{error, _} ->
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Acc
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end,
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scan(I2C, Addr + 1, NewAcc).

‎examples/erlang/rp2/pico_lis3dh.erl‎

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%
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% This file is part of AtomVM.
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%
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% Copyright 2026 Paul Guyot <pguyot@kallisys.net>
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%
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% Licensed under the Apache License, Version 2.0 (the "License");
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% you may not use this file except in compliance with the License.
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% You may obtain a copy of the License at
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%
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% http://www.apache.org/licenses/LICENSE-2.0
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%
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% Unless required by applicable law or agreed to in writing, software
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% distributed under the License is distributed on an "AS IS" BASIS,
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% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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% See the License for the specific language governing permissions and
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% limitations under the License.
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%
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% SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
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%
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%%-----------------------------------------------------------------------------
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%% @doc LIS3DH accelerometer example for Pico.
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%%
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%% Reads X, Y, Z acceleration from a LIS3DH connected via I2C and prints
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%% the values every second.
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%%
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%% Default wiring (Pico pin numbers):
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%% SDA -> GP4 (pin 6)
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%% SCL -> GP5 (pin 7)
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%%
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%% These are the default I2C0 pins on the Pico.
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%% @end
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%%-----------------------------------------------------------------------------
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-module(pico_lis3dh).
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-export([start/0]).
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%% I2C pins (I2C0 default on Pico)
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-define(SDA_PIN, 4).
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-define(SCL_PIN, 5).
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%% LIS3DH I2C address (0x18 when SDO/SA0 is low, 0x19 when high)
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-define(LIS3DH_ADDR, 16#19).
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%% LIS3DH registers
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-define(WHO_AM_I, 16#0F).
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-define(CTRL_REG1, 16#20).
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-define(CTRL_REG4, 16#23).
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-define(OUT_X_L, 16#28).
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%% Expected WHO_AM_I response
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-define(LIS3DH_ID, 16#33).
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start() ->
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I2C = i2c:open([
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{scl, ?SCL_PIN},
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{sda, ?SDA_PIN},
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{clock_speed_hz, 400000},
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{peripheral, 0}
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]),
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case check_who_am_i(I2C) of
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ok ->
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configure(I2C),
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loop(I2C);
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{error, Reason} ->
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console:puts("LIS3DH not found: "),
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console:puts(erlang:atom_to_list(Reason)),
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console:puts("\n")
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end.
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check_who_am_i(I2C) ->
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case i2c:read_bytes(I2C, ?LIS3DH_ADDR, ?WHO_AM_I, 1) of
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{ok, <<?LIS3DH_ID:8>>} ->
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console:puts("LIS3DH detected\n"),
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ok;
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{ok, <<Other:8>>} ->
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console:puts("Unexpected WHO_AM_I: "),
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console:puts(erlang:integer_to_list(Other, 16)),
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console:puts("\n"),
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{error, unexpected_id};
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{error, _} = Error ->
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Error
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end.
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configure(I2C) ->
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%% CTRL_REG1: 50 Hz ODR, normal mode, X/Y/Z enabled
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%% Bits: ODR=0100 LPen=0 Zen=1 Yen=1 Xen=1 -> 0x47
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ok = i2c:write_bytes(I2C, ?LIS3DH_ADDR, ?CTRL_REG1, 16#47),
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%% CTRL_REG4: +/- 2g full scale, high resolution
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%% Bits: BDU=1 BLE=0 FS=00 HR=1 ST=00 SIM=0 -> 0x88
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ok = i2c:write_bytes(I2C, ?LIS3DH_ADDR, ?CTRL_REG4, 16#88).
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loop(I2C) ->
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case read_acceleration(I2C) of
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{ok, {X, Y, Z}} ->
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console:puts("X="),
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console:puts(erlang:integer_to_list(X)),
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console:puts(" Y="),
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console:puts(erlang:integer_to_list(Y)),
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console:puts(" Z="),
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console:puts(erlang:integer_to_list(Z)),
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console:puts("\n");
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{error, Reason} ->
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console:puts("Read error: "),
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console:puts(erlang:atom_to_list(Reason)),
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console:puts("\n")
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end,
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timer:sleep(1000),
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loop(I2C).
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read_acceleration(I2C) ->
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%% Read 6 bytes starting at OUT_X_L with auto-increment (bit 7 set)
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case i2c:read_bytes(I2C, ?LIS3DH_ADDR, ?OUT_X_L bor 16#80, 6) of
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{ok, <<XL:8, XH:8/signed, YL:8, YH:8/signed, ZL:8, ZH:8/signed>>} ->
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%% 12-bit left-justified in high-resolution mode: shift right by 4
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X = ((XH bsl 8) bor XL) bsr 4,
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Y = ((YH bsl 8) bor YL) bsr 4,
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Z = ((ZH bsl 8) bor ZL) bsr 4,
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{ok, {X, Y, Z}};
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{error, _} = Error ->
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Error
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end.

‎libs/avm_rp2/src/CMakeLists.txt‎

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set(ERLANG_MODULES
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gpio
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i2c
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pico
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)
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‎libs/avm_rp2/src/gpio.erl‎

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-export([
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init/1,
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deinit/1,
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set_function/2,
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set_pin_mode/2,
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set_pin_pull/2,
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digital_write/2,
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%% The pin definition for RP2040 is a non-negative integer. A tuple is used for the extra "WL" pins on the Pico-W.
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-type pin_tuple() :: {wl, 0..2}.
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%% The extra "WL" pins on Pico-W use bank `wl'.
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-type gpio_function() :: spi | uart | i2c | pwm | sio | pio0 | pio1.
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%% GPIO function select values matching Pico SDK gpio_function_t.
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-type direction() :: input | output | output_od.
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%% The direction is used to set the mode of operation for a GPIO pin, either as an input, an output, or output with open drain.
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-type pull() :: up | down | up_down | floating.
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deinit(_Pin) ->
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ok.
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%%-----------------------------------------------------------------------------
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%% @param Pin GPIO pin number
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%% @param Function the function to assign to the pin
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%% @returns ok
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%% @doc Select the function for a GPIO pin.
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%%
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%% Maps to `gpio_set_function()' in the Pico SDK.
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%% Common functions: `sio' (default GPIO), `i2c', `spi', `uart', `pwm'.
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%% @end
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%%-----------------------------------------------------------------------------
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-spec set_function(Pin :: non_neg_integer(), Function :: gpio_function()) -> ok.
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set_function(_Pin, _Function) ->
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erlang:nif_error(undefined).
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%%-----------------------------------------------------------------------------
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%% @param Pin number to set operational mode
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%% @param Direction is `input', `output', or `output_od'

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