teensy-4_nxp_iMXRT1062

This repository implements an entirely manually-written, pure bare metal Blinky Project for the NXP ARM Cortex-M7 iMXRT1062 (on the Teensy 4.0 board).

Features include:

• boot through the board's standard bootloader,
• PLL frequency increased to 600 MHz,
• timebase derived from SysTick,
• blinky LED show with adjustable frequency,
• implementation in C++20/C11 (and beyond) with absolute minimal use of assembly.

A clear and easy-to-understand build system based on GNUmake completes this fun and educational project.

This repository provides keen insight on starting up a bare metal Teensy board.

Details on the Application

The application boots from the board's standard bootloader. Necessary inputs/user-adaptions for this boot are provided in the file bootdata.c.

Following the bootloader's low-level chip initialization, the program jumps to our own self-written startup stub called __my_startup() in crt0.cpp.

After a few more initializations in __my_startup(), control is transfered to main(). Here the simple LED blinky show is executed.

The adjustable LED-phase (its half-period) can be tuned to provide a rudimentary, visible blinky LED show. The timebase for blinky is based on the standard SysTick interrupt handler.

Building the Application

The home directory of the build system (whether on Win* of *nix*) is located in the directory Build/VS. Several paths used in the build(s) are defined relative to this home directory.

Build on *nix*

Build on *nix* is easy using an installed gcc-arm-none-eabi

cd teensy-4_nxp_iMXRT1062/Build/VS
../build.sh all

If gcc-arm-none-eabi is not present, then it can be installed (if needed).

sudo apt install gcc-arm-none-eabi

Build on Win* in MSVC

Important: When building with MSVC, it is necessary to first unpack the gcc-arm-none-eabi toolchain. This is done by going to Build/tools/gcc in Windows-Explorer and simply double-clicking on the self-extracting archive file gcc-11.2.0-arm-none-eabi.exe. Answer yes to the query in the pop-up window launched from the extractor.

We will now build the target configuration in MSVC. (This is the configuration that runs on the Teensy board.)

Navigate to the directory Build/VS. Find there the MSVC solution file teensy-4_nxp_iMXRT1062.sln and open it. Select the solution configuration target and rebuild the solution.

The build results including ELF-file, HEX-mask, symbol-file and assembly list file are created in the output directory Build\Bin\target_x64.

There are additional host configurations available.

Simulated Windows (host) project configurations Debug and Release can be used for trouble-shooting the code if needed. These run on the host system with simulated LED blinky show.

Continuous Integration

CI runs on pushes and pull-requests with simple build(s) including result verification on both windows-latest as well as ubuntu-latest using GitHub Actions.

Hardware Setup

The Teensy 4.0 is used with no modifications whatsoever straight out-of-the-box. The hardware setup in action is pictured in the image below.

Licensing

This software project is licensed under BSL 1.0.