Building an Embedded Program

The following command cross compiles the program to the ARM Cortex-M4 architecture. The --target arguments instructs Cargo to cross compile the program.

$ cargo build --target thumbv7em-none-eabi --bin hello

The default in a new Cargo project is to compile for the host (native compilation). Within the beginner/apps folder you can however omit the --target flag and Cargo will still cross compile for the ARM Cortex-M4 architecture.

$ cargo build --bin hello

The reason for this is that the default compilation target has been set to ARM Cortex-M4 in the Cargo configuration file (.cargo/config):

# .cargo/config
[build]
target = "thumbv7em-none-eabi"

The output of the compilation process will be an ELF (Executable and Linkable Format) file. The file will be placed in the beginner/apps/target directory. To display the amount of Flash the program will occupy on the target device use the rust-size tool (part of the cargo-binutils package):

$ rust-size target/thumbv7em-none-eabi/debug/hello
   text    data     bss     dec     hex filename
  14564       8    2124   16696    4138 target/thumbv7em-none-eabi/debug/hello

14460 bytes is the amount of Flash memory the program will occupy.

Alternatively, you can run the cargo-size subcommand, which will build the program before displaying the size of the binary.

$ cargo size --bin hello
   text    data     bss     dec     hex filename
  14564       8    2124   16696    4138 hello

Passing the -A flag to rust-size or cargo-size will give a more detailed breakdown of the static memory usage:

$ # omit the `--` flag if using `rust-size`
$ cargo size --bin hello -- -A
hello  :
section              size        addr
.vector_table         256         0x0
.text                9740       0x100
.rodata              4568      0x270c
.data                   8  0x20000000
.bss                 2124  0x20000008
.uninit                 0  0x20000854

The .vector_table section contains the vector table, a data structure required by the Cortex-M ISA. The .text section contains the instructions the program will execute. The .rodata section contains constants like strings literals. These three sections are contiguously located in Flash memory -- Flash memory spans from address 0x0000_0000 to 0x0010_0000 (1 MB).

The next three sections, .data, .bss and .uninit, are located in RAM -- RAM memory spans the address range 0x2000_0000 - 0x2004_0000 (256 KB). These sections contain statically allocated variables (static variables).

2.6 KiB Raw Blame History

Building an Embedded Program

2.6 KiB

Raw Blame History