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Add UART support to RP2 platform
Also add a sample code, `sim800l.erl` confirmed to work on both Pico-W and ESP32C2, using the same high level UART API. Signed-off-by: Paul Guyot <pguyot@kallisys.net>
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‎examples/erlang/CMakeLists.txt‎

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@@ -43,3 +43,4 @@ pack_runnable(logging_example logging_example estdlib eavmlib)
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pack_runnable(http_client http_client estdlib eavmlib avm_network)
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pack_runnable(disterl disterl estdlib)
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pack_runnable(spi_flash spi_flash eavmlib estdlib DIALYZE_AGAINST avm_esp32 avm_rp2)
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pack_runnable(sim800l sim800l eavmlib estdlib DIALYZE_AGAINST avm_esp32 avm_rp2)

‎examples/erlang/rp2/CMakeLists.txt‎

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@@ -38,6 +38,17 @@ add_custom_command(
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)
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add_custom_target(spi_flash_uf2 ALL DEPENDS spi_flash.uf2)
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add_dependencies(spi_flash_uf2 spi_flash)
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set(SIM800L_AVM ${CMAKE_BINARY_DIR}/examples/erlang/sim800l.avm)
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add_custom_command(
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OUTPUT sim800l.uf2
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DEPENDS ${SIM800L_AVM} UF2Tool
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COMMAND ${CMAKE_BINARY_DIR}/tools/uf2tool/uf2tool create -o sim800l.uf2 -f universal -s 0x10180000 ${SIM800L_AVM}
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COMMENT "Creating UF2 file sim800l.uf2"
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VERBATIM
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)
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add_custom_target(sim800l_uf2 ALL DEPENDS sim800l.uf2)
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add_dependencies(sim800l_uf2 sim800l)
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pack_uf2(picow_blink picow_blink)
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pack_uf2(picow_wifi_sta picow_wifi_sta)
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pack_uf2(picow_wifi_ap picow_wifi_ap)

‎examples/erlang/sim800l.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 SIM800L AT command demo.
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%%
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%% Opens a UART connection to a SIM800L GSM module and verifies it responds
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%% to basic AT commands. Prints firmware identification and signal quality
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%% every 10 seconds.
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%%
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%% Be careful: SIM800L boards can draw up to 2A and shouldn't be powered by
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%% the 3.3V of the usual Pico / ESP32 boards. It's ok for this demo but
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%% do not put a SIM card in them to avoid damaging your board.
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%%
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%% The SIM800L communicates at 115200 baud (8N1) by default.
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%%
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%% Default pins are auto-detected from the platform and chip model:
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%%
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%% Pico (UART1): TX=GP4, RX=GP5
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%% ESP32/S2/S3 (UART1): TX=17, RX=16
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%% ESP32-C3/C5 (UART1): TX=4, RX=5
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%% ESP32-C6/C61 (UART1): TX=4, RX=5
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%% @end
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%%-----------------------------------------------------------------------------
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-module(sim800l).
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-export([start/0]).
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-define(AT_TIMEOUT, 2000).
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start() ->
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{TX, RX} = default_pins(),
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io:format("Opening UART1 on TX=~B RX=~B~n", [TX, RX]),
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UART = uart:open("UART1", [
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{tx, TX},
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{rx, RX},
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{speed, 115200}
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]),
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%% SIM800L takes 3-5 seconds to boot after power-on
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case wait_for_module(UART, 5) of
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ok ->
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io:format("SIM800L responding to AT commands~n"),
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at_identify(UART),
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loop(UART);
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error ->
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io:format("SIM800L not responding, giving up~n"),
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uart:close(UART)
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end.
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loop(UART) ->
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at_signal_quality(UART),
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timer:sleep(10000),
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loop(UART).
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wait_for_module(_UART, 0) ->
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error;
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wait_for_module(UART, Retries) ->
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drain(UART),
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case at_command(UART, <<"AT">>) of
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{ok, _} ->
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ok;
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{error, _} ->
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timer:sleep(1000),
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wait_for_module(UART, Retries - 1)
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end.
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at_identify(UART) ->
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case at_command(UART, <<"ATI">>) of
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{ok, Response} ->
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io:format("Module info: ~s~n", [Response]);
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{error, Reason} ->
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io:format("ATI failed: ~p~n", [Reason])
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end.
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at_signal_quality(UART) ->
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case at_command(UART, <<"AT+CSQ">>) of
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{ok, Response} ->
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io:format("Signal quality: ~s~n", [Response]);
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{error, Reason} ->
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io:format("AT+CSQ failed: ~p~n", [Reason])
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end.
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%%-----------------------------------------------------------------------------
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%% @private Send an AT command and collect the response until OK or ERROR.
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%%-----------------------------------------------------------------------------
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at_command(UART, Command) ->
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uart:write(UART, [Command, <<"\r\n">>]),
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collect_response(UART, []).
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collect_response(UART, Acc) ->
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case uart:read(UART, ?AT_TIMEOUT) of
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{ok, Data} ->
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NewAcc = [Data | Acc],
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Combined = erlang:iolist_to_binary(lists:reverse(NewAcc)),
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case parse_response(Combined) of
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{ok, Body} -> {ok, Body};
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error -> {error, Combined};
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incomplete -> collect_response(UART, NewAcc)
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end;
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{error, timeout} when Acc =/= [] ->
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Combined = erlang:iolist_to_binary(lists:reverse(Acc)),
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case parse_response(Combined) of
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{ok, Body} -> {ok, Body};
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_ -> {error, {partial, Combined}}
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end;
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{error, timeout} ->
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{error, timeout}
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end.
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%% Look for OK or ERROR in the accumulated response
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parse_response(Data) ->
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case binary:match(Data, <<"\r\nOK\r\n">>) of
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{_Pos, _Len} ->
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Body = strip_status(Data),
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{ok, Body};
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nomatch ->
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case binary:match(Data, <<"\r\nERROR\r\n">>) of
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{_Pos2, _Len2} -> error;
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nomatch -> incomplete
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end
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end.
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%% Extract body between echo/first CRLF and final status line
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strip_status(Data) ->
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Trimmed = trim_leading_crlf(Data),
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case binary:match(Trimmed, <<"\r\nOK\r\n">>) of
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{Pos, _} -> binary:part(Trimmed, 0, Pos);
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nomatch -> Trimmed
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end.
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trim_leading_crlf(<<"\r\n", Rest/binary>>) -> trim_leading_crlf(Rest);
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trim_leading_crlf(Data) -> Data.
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%% Discard any pending data in the UART buffer
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drain(UART) ->
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case uart:read(UART, 100) of
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{ok, _} -> drain(UART);
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{error, timeout} -> ok
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end.
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%%-----------------------------------------------------------------------------
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%% Platform-specific default pins
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%%-----------------------------------------------------------------------------
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default_pins() ->
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default_pins(atomvm:platform()).
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%% {TX, RX}
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default_pins(pico) -> {4, 5};
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default_pins(esp32) -> esp32_default_pins().
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esp32_default_pins() ->
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#{model := Model} = erlang:system_info(esp32_chip_info),
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esp32_default_pins(Model).
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%% {TX, RX}
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esp32_default_pins(esp32) -> {17, 16};
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esp32_default_pins(esp32_s2) -> {17, 16};
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esp32_default_pins(esp32_s3) -> {17, 16};
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esp32_default_pins(esp32_c2) -> {4, 5};
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esp32_default_pins(esp32_c3) -> {4, 5};
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esp32_default_pins(esp32_c5) -> {4, 5};
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esp32_default_pins(esp32_c6) -> {4, 5};
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esp32_default_pins(esp32_c61) -> {4, 5};
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esp32_default_pins(_) -> {17, 16}.

‎libs/avm_rp2/src/CMakeLists.txt‎

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i2c
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pico
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spi
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uart
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)
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pack_archive(avm_rp2 DEPENDS_ON eavmlib ERLC_FLAGS +warnings_as_errors MODULES ${ERLANG_MODULES})

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