Adds Proton C Conversion (#4661)

* adds proton c base

* fixes custom matrix include

* adds readme.md

* initial proton coversion, no pin mapping

* start of mcu selection

* add pin mapping and sweet16 test

* add at90 to list

* disable backlight, fix d7

* update flag names

* doc updates

* proton c update for mcu selection

quantum/mcu_selection.mk

@@ -0,0 +1,70 @@
+
+ifneq ($(findstring STM32F303, $(MCU)),)
+  ## chip/board settings
+  # - the next two should match the directories in
+  #   <chibios>/os/hal/ports/$(MCU_FAMILY)/$(MCU_SERIES)
+  MCU_FAMILY ?= STM32
+  MCU_SERIES ?= STM32F3xx
+
+  # Linker script to use
+  # - it should exist either in <chibios>/os/common/ports/ARMCMx/compilers/GCC/ld/
+  #   or <this_dir>/ld/
+  MCU_LDSCRIPT ?= STM32F303xC
+
+  # Startup code to use
+  #  - it should exist in <chibios>/os/common/startup/ARMCMx/compilers/GCC/mk/
+  MCU_STARTUP ?= stm32f3xx
+
+  # Board: it should exist either in <chibios>/os/hal/boards/
+  #  or <this_dir>/boards
+  BOARD ?= GENERIC_STM32_F303XC
+
+  # Cortex version
+  MCU = cortex-m4
+
+  # ARM version, CORTEX-M0/M1 are 6, CORTEX-M3/M4/M7 are 7
+  ARMV ?= 7
+
+  USE_FPU = yes
+
+  # Vector table for application
+  # 0x00000000-0x00001000 area is occupied by bootlaoder.*/
+  # The CORTEX_VTOR... is needed only for MCHCK/Infinity KB
+  # OPT_DEFS = -DCORTEX_VTOR_INIT=0x08005000
+
+  # Options to pass to dfu-util when flashing
+  DFU_ARGS ?= -d 0483:df11 -a 0 -s 0x08000000:leave
+endif
+
+ifneq (,$(filter $(MCU),atmega32u4 at90usb1286))
+  # Processor frequency.
+  #     This will define a symbol, F_CPU, in all source code files equal to the
+  #     processor frequency in Hz. You can then use this symbol in your source code to
+  #     calculate timings. Do NOT tack on a 'UL' at the end, this will be done
+  #     automatically to create a 32-bit value in your source code.
+  #
+  #     This will be an integer division of F_USB below, as it is sourced by
+  #     F_USB after it has run through any CPU prescalers. Note that this value
+  #     does not *change* the processor frequency - it should merely be updated to
+  #     reflect the processor speed set externally so that the code can use accurate
+  #     software delays.
+  F_CPU ?= 16000000
+
+  # LUFA specific
+  #
+  # Target architecture (see library "Board Types" documentation).
+  ARCH ?= AVR8
+
+  # Input clock frequency.
+  #     This will define a symbol, F_USB, in all source code files equal to the
+  #     input clock frequency (before any prescaling is performed) in Hz. This value may
+  #     differ from F_CPU if prescaling is used on the latter, and is required as the
+  #     raw input clock is fed directly to the PLL sections of the AVR for high speed
+  #     clock generation for the USB and other AVR subsections. Do NOT tack on a 'UL'
+  #     at the end, this will be done automatically to create a 32-bit value in your
+  #     source code.
+  #
+  #     If no clock division is performed on the input clock inside the AVR (via the
+  #     CPU clock adjust registers or the clock division fuses), this will be equal to F_CPU.
+  F_USB ?= $(F_CPU)
+endif