README
======

This is the README file for a port of NuttX to the ST Micro B-G474E-DPOW1
Discovery kit with STM32G474RE MCU. For more information about this board,
see:

  https://www.st.com/content/st_com/en/products/evaluation-tools/product-evaluation-tools/mcu-mpu-eval-tools/stm32-mcu-mpu-eval-tools/stm32-discovery-kits/b-g474e-dpow1.html

Contents
========

  - Status
  - Development Environment
    - Toolchains
    - Debugging
  - Hardware
    - MCU Clocking
    - GPIOs
    - Buttons
    - LEDs
    - RGB Power LED
  - Serial Consoles
  - FLASH Bootloader Support
  - Configurations

Status
======

  This port boots NuttX through to a functional NSH prompt.

Development Environment
=======================

  Toolchains
  ----------
  An appropriate ARM toolchain is needed, such as the one built with the
  customized NuttX buildroot or the ready-made GNU Tools for Arm Embedded
  Processors.

  Debugging
  ---------
  The board incorporates a STLINK-V3E programmer/debugger accessible via the
  Micro-USB Type B connector.

  To debug with OpenOCD and arm-nuttx-eabi-gdb:

  * Use 'make menuconfig' to set CONFIG_DEBUG_SYMBOLS and CONFIG_DEBUG_NOOPT.
    To see debug output, e.g., the "ABCDE" printed in __start(), also set
    CONFIG_DEBUG_FEATURES.

  * Build NuttX.

  * Flash the code using:
    $ openocd -f interface/stlink.cfg -f target/stm32g4x.cfg -c init \
      -c "reset halt" -c "flash write_image erase nuttx.bin 0x08000000"

    NOTE: The above command might fail unless either: udev rules have been
    configured on the development system (preferred) or the command is run as
    root with 'sudo' (not encouraged). See:
    - https://openocd.org/doc/html/Running.html
    - https://forgge.github.io/theCore/guides/running-openocd-without-sudo.html

  * Start GDB with:
    $ arm-nuttx-eabi-gdb -tui nuttx

  * In GDB:
    (gdb) target remote localhost:3333
    (gdb) monitor reset halt
    (gdb) load

Hardware
========

  MCU Clocking
  ------------
  By default, the MCU on this board is clocked from the MCU's internal HSI
  clock, and only this option is supported by software at this time.

  If software support is added for it, the MCU could be clocked from the
  following other sources: a 24 MHz oscillator on X2, MCO from STLINK-V3E, or
  external clock from connector CN9, pin 26.

  GPIOs
  -----

  Buttons
  -------
  The board has 5 user buttons in the form of a 4-direction "joystick" with a
  selection button (pressing down on the "joystick").

  LEDs
  ----
  The board has 4 user LEDs.

  RGB Power LED
  -------------
  The board has a super bright RGB power LED.

  Caution: For eye safety, ensure that the power LED is covered by the
  diffuser that comes installed over it.

Serial Consoles
===============

  The MCU's USART3 is connected to the on-board STLINK-V3E and exposed to
  the PC as a Virtual COM Port over the same Micro-USB Type B connection used
  for programming/debugging.

  On Debian Linux, this shows up as /dev/ttyACM0. Other operating systems may
  differ.

FLASH Bootloader Support
========================

  If implementing a FLASH bootloader, turn on Kconfig option CONFIG_STM32_DFU.
  This option activates an alternate linker script, scripts/ld.script.dfu,
  which causes NuttX to leave a gap at the start of FLASH, leaving that space
  for the FLASH bootloader. See scripts/ld.script.dfu for details. It also
  causes NuttX to relocate its vector table and possibly make other
  adjustments.

  One possible bootloader is STmicro's OpenBootloader "middleware" supplied
  with STM32CubeG4 version 1.3.0. On the host (PC), it should be possible to
  use STmicro's STM32CubeProgrammer or the stm32loader.py script from
  https://github.com/jsnyder/stm32loader. That script can be invoked with
  parameters such as:

    stm32loader.py -p /dev/ttyACM0 -a 0x08006000 -e -w -v -g 0x08006000 nuttx.bin

  where the given address (0x08006000 in this case) must match the starting
  address in scripts/ld.script.dfu.

Configurations
==============

  nsh
  ---