Add beginnings of software implementation

 - Software is based off my wifi pc remote button code, as well as my
   old SNES STM32 controller converter code for the TinyUSB descriptor.
 - This code relies on the following upstream PRs:
   - raspberrypi/pico-sdk#1530
   - FreeRTOS/FreeRTOS-Kernel#991
   - raspberrypi/pico-sdk#1635

LICENSE

@@ -10,5 +10,9 @@ with or without fee is hereby granted." There are some exceptions, but I do not
 believe we are using any of the models/designs from other manufacturers that
 fall under those exceptions.
 
-The rest of the files are licensed under the CERN Open Hardware Licence Version
-2 - Weakly Reciprocal.
+The KiCAD PCB design files are licensed under the CERN Open Hardware Licence
+Version 2 - Weakly Reciprocal.
+
+The software under the firmware folder is licensed under the GPL v2.0 or later,
+or the LGPL v2.1 or later. More details can be found in the firmware/LICENSE
+file.

firmware/.gitignore

@@ -0,0 +1,2 @@
+/include/secrets.h
+/build

firmware/CMakeLists.txt

@@ -0,0 +1,54 @@
+cmake_minimum_required(VERSION 3.20)
+
+include(pico_sdk_import.cmake)
+include(FreeRTOS_Kernel_import.cmake)
+
+project(snes_controllers_to_usb)
+
+pico_sdk_init()
+
+add_executable(snes_controllers_to_usb
+	src/main.cpp
+	src/log.cpp
+	src/server.cpp
+	src/network_task.cpp
+	src/cli_task.cpp
+	src/FreeRTOS_support.cpp
+	src/usb_descriptors.c
+	src/syscalls.cpp
+)
+
+target_link_libraries(snes_controllers_to_usb
+	pico_cyw43_arch_lwip_sys_freertos
+	pico_stdlib
+	pico_rand
+	FreeRTOS-Kernel-Heap3
+	tinyusb_device
+	tinyusb_board
+)
+
+target_compile_options(snes_controllers_to_usb PRIVATE
+	$<$<CXX_COMPILER_ID:MSVC>:/W4>
+	$<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wall -Wextra>
+	-fstack-usage
+	-Wno-psabi
+)
+
+target_include_directories(snes_controllers_to_usb PRIVATE
+	${CMAKE_SOURCE_DIR}/include
+)
+
+target_compile_features(snes_controllers_to_usb PRIVATE
+	cxx_std_23
+)
+
+pico_set_printf_implementation(snes_controllers_to_usb compiler)
+pico_set_stdio_implementation(snes_controllers_to_usb compiler)
+
+set_property(TARGET snes_controllers_to_usb PROPERTY CXX_STANDARD 23)
+
+if (DEFINED HOSTNAME)
+	add_compile_definitions(CYW43_HOST_NAME=\"${HOSTNAME}\")
+endif()
+
+pico_add_extra_outputs(snes_controllers_to_usb)

firmware/FreeRTOS_Kernel_import.cmake

@@ -0,0 +1,61 @@
+# This is a copy of <FREERTOS_KERNEL_PATH>/portable/ThirdParty/GCC/RP2040/FREERTOS_KERNEL_import.cmake
+
+# This can be dropped into an external project to help locate the FreeRTOS kernel
+# It should be include()ed prior to project(). Alternatively this file may
+# or the CMakeLists.txt in this directory may be included or added via add_subdirectory
+# respectively.
+
+if (DEFINED ENV{FREERTOS_KERNEL_PATH} AND (NOT FREERTOS_KERNEL_PATH))
+    set(FREERTOS_KERNEL_PATH $ENV{FREERTOS_KERNEL_PATH})
+    message("Using FREERTOS_KERNEL_PATH from environment ('${FREERTOS_KERNEL_PATH}')")
+endif ()
+
+set(FREERTOS_KERNEL_RP2040_RELATIVE_PATH "portable/ThirdParty/GCC/RP2040")
+# undo the above
+set(FREERTOS_KERNEL_RP2040_BACK_PATH "../../../..")
+
+if (NOT FREERTOS_KERNEL_PATH)
+    # check if we are inside the FreeRTOS kernel tree (i.e. this file has been included directly)
+    get_filename_component(_ACTUAL_PATH ${CMAKE_CURRENT_LIST_DIR} REALPATH)
+    get_filename_component(_POSSIBLE_PATH ${CMAKE_CURRENT_LIST_DIR}/${FREERTOS_KERNEL_RP2040_BACK_PATH}/${FREERTOS_KERNEL_RP2040_RELATIVE_PATH} REALPATH)
+    if (_ACTUAL_PATH STREQUAL _POSSIBLE_PATH)
+        get_filename_component(FREERTOS_KERNEL_PATH ${CMAKE_CURRENT_LIST_DIR}/${FREERTOS_KERNEL_RP2040_BACK_PATH} REALPATH)
+    endif()
+    if (_ACTUAL_PATH STREQUAL _POSSIBLE_PATH)
+        get_filename_component(FREERTOS_KERNEL_PATH ${CMAKE_CURRENT_LIST_DIR}/${FREERTOS_KERNEL_RP2040_BACK_PATH} REALPATH)
+        message("Setting FREERTOS_KERNEL_PATH to ${FREERTOS_KERNEL_PATH} based on location of FreeRTOS-Kernel-import.cmake")
+    elseif (PICO_SDK_PATH AND EXISTS "${PICO_SDK_PATH}/../FreeRTOS-Kernel")
+        set(FREERTOS_KERNEL_PATH ${PICO_SDK_PATH}/../FreeRTOS-Kernel)
+        message("Defaulting FREERTOS_KERNEL_PATH as sibling of PICO_SDK_PATH: ${FREERTOS_KERNEL_PATH}")
+    endif()
+endif ()
+
+if (NOT FREERTOS_KERNEL_PATH)
+    foreach(POSSIBLE_SUFFIX Source FreeRTOS-Kernel FreeRTOS/Source)
+        # check if FreeRTOS-Kernel exists under directory that included us
+        set(SEARCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR})
+        get_filename_component(_POSSIBLE_PATH ${SEARCH_ROOT}/${POSSIBLE_SUFFIX} REALPATH)
+        if (EXISTS ${_POSSIBLE_PATH}/${FREERTOS_KERNEL_RP2040_RELATIVE_PATH}/CMakeLists.txt)
+            get_filename_component(FREERTOS_KERNEL_PATH ${_POSSIBLE_PATH} REALPATH)
+            message("Setting FREERTOS_KERNEL_PATH to '${FREERTOS_KERNEL_PATH}' found relative to enclosing project")
+            break()
+        endif()
+    endforeach()
+endif()
+
+if (NOT FREERTOS_KERNEL_PATH)
+    message(FATAL_ERROR "FreeRTOS location was not specified. Please set FREERTOS_KERNEL_PATH.")
+endif()
+
+set(FREERTOS_KERNEL_PATH "${FREERTOS_KERNEL_PATH}" CACHE PATH "Path to the FreeRTOS Kernel")
+
+get_filename_component(FREERTOS_KERNEL_PATH "${FREERTOS_KERNEL_PATH}" REALPATH BASE_DIR "${CMAKE_BINARY_DIR}")
+if (NOT EXISTS ${FREERTOS_KERNEL_PATH})
+    message(FATAL_ERROR "Directory '${FREERTOS_KERNEL_PATH}' not found")
+endif()
+if (NOT EXISTS ${FREERTOS_KERNEL_PATH}/${FREERTOS_KERNEL_RP2040_RELATIVE_PATH}/CMakeLists.txt)
+    message(FATAL_ERROR "Directory '${FREERTOS_KERNEL_PATH}' does not contain an RP2040 port here: ${FREERTOS_KERNEL_RP2040_RELATIVE_PATH}")
+endif()
+set(FREERTOS_KERNEL_PATH ${FREERTOS_KERNEL_PATH} CACHE PATH "Path to the FreeRTOS_KERNEL" FORCE)
+
+add_subdirectory(${FREERTOS_KERNEL_PATH}/${FREERTOS_KERNEL_RP2040_RELATIVE_PATH} FREERTOS_KERNEL)

firmware/LICENSE

@@ -0,0 +1,9 @@
+This software is released under the following licenses:
+ - GPL v2 or later
+ - LGPL v2.1 or later
+
+You should be able to find the text to the GPL v2, GPL v3, LGPL v2.1, and LGPL
+v3.0 licenses in the root directory of this repository.
+
+At the time of this writing all of the available licenses could be found on
+https://www.gnu.org/licenses/licenses.html