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    //! A template for building applications for ARM Cortex-M microcontrollers
    //!
    //! # Dependencies
    //!
    //! - Nightly Rust toolchain from 2018-08-28 or newer: `rustup default nightly`
    //! - Cargo `clone` subcommand: `cargo install cargo-clone`
    //! - GDB: `sudo apt-get install gdb-arm-none-eabi` (on Ubuntu)
    //! - OpenOCD: `sudo apt-get install OpenOCD` (on Ubuntu)
    //! - [Optional] Cargo `add` subcommand: `cargo install cargo-edit`
    //!
    //! # Usage
    //!
    //! 0) Figure out the cross compilation *target* to use.
    //!
    //! - Use `thumbv6m-none-eabi` for ARM Cortex-M0 and Cortex-M0+
    //! - Use `thumbv7m-none-eabi` for ARM Cortex-M3
    //! - Use `thumbv7em-none-eabi` for ARM Cortex-M4 and Cortex-M7 (*no* FPU support)
    //! - Use `thumbv7em-none-eabihf` for ARM Cortex-M4**F** and Cortex-M7**F** (*with* FPU support)
    //!
    //! 1) Install the `rust-std` component for your target, if you haven't done so already
    //!
    //! ``` console
    //! $ rustup target add thumbv7em-none-eabihf
    //! ```
    //!
    //! 2) Clone this crate
    //!
    //! ``` text
    //! $ cargo clone cortex-m-quickstart --vers 0.3.4
    //! ```
    //!
    //! 3) Change the crate name, author and version
    //!
    //! ``` text
    //! $ edit Cargo.toml && head $_
    //! [package]
    //! authors = ["Jorge Aparicio <jorge@japaric.io>"]
    //! name = "demo"
    //! version = "0.1.0"
    //! ```
    //!
    //! 4) Specify the memory layout of the target device
    //!
    //! **NOTE** board support crates sometimes provide this file for you (check the crate
    //! documentation). If you are using one that does then remove *both* `memory.x` and `build.rs` from
    //! the root of this crate.
    //!
    //! ``` text
    //! $ cat >memory.x <<'EOF'
    //! MEMORY
    //! {
    //!   /* NOTE K = KiBi = 1024 bytes */
    //!   FLASH : ORIGIN = 0x08000000, LENGTH = 256K
    //!   RAM : ORIGIN = 0x20000000, LENGTH = 40K
    //! }
    //! EOF
    //! ```
    //!
    //! 5) Optionally, set a default build target. This way you don't have to pass `--target` to each
    //! Cargo invocation.
    //!
    //! ``` text
    //! $ cat >>.cargo/config <<'EOF'
    //! [build]
    //! target = "thumbv7em-none-eabihf"
    //! EOF
    //! ```
    //!
    //! 6) Optionally, depend on a device, HAL implementation or a board support crate.
    //!
    //! ``` text
    //! $ # add a device crate, OR
    //! $ cargo add stm32f30x
    //!
    //! $ # add a HAL implementation crate, OR
    //! $ cargo add stm32f30x-hal
    //!
    //! $ # add a board support crate
    //! $ cargo add f3
    //! ```
    //!
    //! 7) Write the application or start from one of the examples
    //!
    //! ``` text
    //! $ rm -r src/* && cp examples/hello.rs src/main.rs
    //! ```
    //!
    //! 8) Build the application
    //!
    //! ``` text
    //! $ cargo build --release
    //!
    //! $ # sanity check
    //! $ arm-none-eabi-readelf -A target/thumbv7em-none-eabihf/release/demo
    //! Attribute Section: aeabi
    //! File Attributes
    //!   Tag_conformance: "2.09"
    //!   Tag_CPU_arch: v7E-M
    //!   Tag_CPU_arch_profile: Microcontroller
    //!   Tag_THUMB_ISA_use: Thumb-2
    //!   Tag_FP_arch: VFPv4-D16
    //!   Tag_ABI_PCS_GOT_use: direct
    //!   Tag_ABI_FP_denormal: Needed
    //!   Tag_ABI_FP_exceptions: Needed
    //!   Tag_ABI_FP_number_model: IEEE 754
    //!   Tag_ABI_align_needed: 8-byte
    //!   Tag_ABI_align_preserved: 8-byte, except leaf SP
    //!   Tag_ABI_HardFP_use: SP only
    //!   Tag_ABI_VFP_args: VFP registers
    //!   Tag_ABI_optimization_goals: Aggressive Speed
    //!   Tag_CPU_unaligned_access: v6
    //!   Tag_FP_HP_extension: Allowed
    //!   Tag_ABI_FP_16bit_format: IEEE 754
    //! ```
    //!
    //! 9) Flash and debug the program
    //!
    //! ``` text
    //! $ # Launch OpenOCD on a terminal
    //! $ openocd -f (..)
    //! ```
    //!
    //! ``` text
    //! $ # Start a debug session in another terminal
    //! $ arm-none-eabi-gdb target/thumbv7em-none-eabihf/release/demo
    //! ```
    //!
    //! Alternatively, you can use `cargo run` to build, flash and debug the program in a single step.
    //!
    //! ``` text
    //! $ cargo run --example hello
    //! > # drops you into a GDB session
    //! ```
    //!
    //! # Examples
    //!
    //! Check the [examples module][examples]
    //!
    //! [examples]: ./examples/index.html
    //!
    //! # Troubleshooting
    //!
    //! This section contains fixes for common errors encountered when the
    //! `cortex-m-quickstart` template is misused.
    //!
    //! ## Used the standard `main` interface
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo build
    //!    Compiling demo v0.1.0 (file:///home/japaric/tmp/demo)
    //!
    //! error: requires `start` lang_item
    //! ```
    //!
    //! Solution: Use `#![no_main]` and `entry!` as shown in the [examples].
    //!
    //! ## Forgot to launch an OpenOCD instance
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ arm-none-eabi-gdb target/..
    //! Reading symbols from hello...done.
    //! .gdbinit:1: Error in sourced command file:
    //! :3333: Connection timed out.
    //! ```
    //!
    //! Solution: Launch OpenOCD on other terminal. See [Usage] section.
    //!
    //! [Usage]: ./index.html#usage
    //!
    //! ## Didn't modify the `memory.x` linker script
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo build
    //! Compiling demo v0.1.0 (file:///home/japaric/tmp/demo)
    //! error: linking with `rust-lld` failed: exit code: 1
    //! |
    //! = note: "rust-lld" "-flavor" "gnu" "-L" (..)
    //! (..)
    //!  = note: rust-lld: error: section '.vector_table' will not fit in region 'FLASH': overflowed by X bytes
    //!          rust-lld: error: section '.vector_table' will not fit in region 'FLASH': overflowed by Y bytes
    //! (..)
    //! ```
    //!
    //! Solution: Specify your device memory layout in the `memory.x` linker script. See [Usage]
    //! section.
    //!
    //! ## Didn't set a default build target and forgot to pass `--target` to Cargo
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo build
    //! (..)
    //! error: language item required, but not found: `eh_personality`
    //!
    //! error: aborting due to previous error
    //! ```
    //!
    //! Solution: Set a default build target in the `.cargo/config` file (see [Usage] section), or call
    //! Cargo with `--target` flag: `cargo build --target thumbv7em-none-eabi`.
    //!
    //! ## Overwrote the original `.cargo/config` file
    //!
    //! You won't get an error message but the output binary will be empty
    //!
    //! ``` text
    //! $ cargo build && echo OK
    //! OK
    //!
    //! $ size target/thumbv7m-none-eabi/debug/app
    //!    text    data     bss     dec     hex filename
    //!       0       0       0       0       0 target/thumbv7m-none-eabi/debug/app
    //! ```
    //!
    //! Solution: You probably overwrote the original `.cargo/config` instead of appending the default
    //! build target (e.g. `cat >` instead of `cat >>`). The less error prone way to fix this is to
    //! remove the `.cargo` directory, clone a new copy of the template and then copy the `.cargo`
    //! directory from that fresh template into your current project. Don't forget to *append* the
    //! default build target to `.cargo/config`.
    //!
    //! ## Called OpenOCD with wrong arguments
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ openocd -f ..
    //! (..)
    //! Error: open failed
    //! in procedure 'init'
    //! in procedure 'ocd_bouncer'
    //! ```
    //!
    //! Solution: Correct the OpenOCD arguments. Check the `/usr/share/openocd/scripts` directory (exact
    //! location varies per distribution / OS) for a list of scripts that can be used.
    //!
    //! ## Forgot to install the `rust-std` component
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo build
    //! error[E0463]: can't find crate for `core`
    //!   |
    //!   = note: the `thumbv7m-none-eabi` target may not be installed
    //! ```
    //!
    //! Solution: call `rustup target add thumbv7m-none-eabi` but with the name of your target
    //!
    //! ## Used an old nightly
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo build
    //! Compiling cortex-m-rt v0.2.0
    //! error[E0463]: can't find crate for `core`
    //! |
    //! = note: the `thumbv7em-none-eabihf` target may not be installed
    //!
    //! error: aborting due to previous error
    //! ```
    //!
    //! Solution: Use a more recent nightly
    //!
    //! ## Used the stable toolchain
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo build
    //! error[E0463]: can't find crate for `core`
    //!   |
    //!   = note: the `thumbv7em-none-eabihf` target may not be installed
    //! ```
    //!
    //! Solution: We are not there yet! Switch to the nightly toolchain with `rustup default nightly`.
    //!
    //! ## Used `gdb` instead of `arm-none-eabi-gdb`
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ gdb target/..
    //! Reading symbols from hello...done.
    //! warning: Architecture rejected target-supplied description
    //! warning: Cannot convert floating-point register value to ..
    //! value has been optimized out
    //! Cannot write the dashboard
    //! Traceback (most recent call last):
    //! File "<string>", line 353, in render
    //! File "<string>", line 846, in lines
    //! gdb.error: Frame is invalid.
    //! 0x00000000 in ?? ()
    //! semihosting is enabled
    //! Loading section .text, size 0xd88 lma 0x8000000
    //! Start address 0x8000000, load size 3464
    //! .gdbinit:6: Error in sourced command file:
    //! Remote connection closed
    //! ```
    //!
    //! Solution: Use `arm-none-eabi-gdb target/..`
    //!
    //! # Used a named piped for `itm.fifo`
    //!
    //! Error message:
    //!
    //! ``` text
    //! $ cargo run [--example ..]
    //!
    //! Reading symbols from target/thumbv7em-none-eabihf/debug/cortex-m-quickstart...done.
    //! cortex_m_rt::reset_handler ()
    //!     at $REGISTRY/cortex-m-rt-0.3.12/src/lib.rs:330
    //! 330     unsafe extern "C" fn reset_handler() -> ! {
    //! semihosting is enabled
    //! Ignoring packet error, continuing...
    //! Ignoring packet error, continuing...
    //! ```
    //!
    //! Note that when you reach this point OpenOCD will become unresponsive and you'll have to kill it
    //! and start a new OpenOCD process before you can invoke `cargo run` / start GDB.
    //!
    //! Cause: You uncommented the `monitor tpiu ..` line in `.gdbinit` and are using a named pipe to
    //! receive the ITM data (i.e. you ran `mkfifo itm.fifo`). This error occurs when `itmdump -f
    //! itm.fifo` (or equivalent, e.g. `cat itm.fifo`) is not running.
    //!
    //! Solution: Run `itmdump -f itm.fifo` (or equivalently `cat itm.fifo`) *before* invoking `cargo
    //! run` / starting GDB. Note that sometimes `itmdump` will exit when the GDB session ends. In that
    //! case you'll have to run `itmdump` before you start the next GDB session.
    //!
    //! Alternative solution: Use a plain text file instead of a named pipe. In this scenario you omit
    //! the `mkfifo itm.dump` command. You can use `itmdump`'s *follow* mode (-F) to get named pipe like
    //! output.

    #![no_std]

    pub mod examples;

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