[−][src]Crate r0
Memory initialization code ("crt0") written in Rust.
This crate is meant for bare metal systems where there is no ELF loader or
OS to take care of initializing RAM for the program. It provides functions
for initializing the .data and .bss sections.
Initializing RAM
On the linker script side, we must assign names (symbols) to the boundaries
of the .bss and .data sections. For example:
.bss : ALIGN(4)
{
_sbss = .;
*(.bss.*);
_ebss = ALIGN(4);
} > RAM
.data : ALIGN(4)
{
_sdata = .;
*(.data.*);
_edata = ALIGN(4);
} > RAM AT > FLASH
_sidata = LOADADDR(.data);
This script defines symbols _sbss/_ebss, and _sdata/_edata to point
at the boundaries of the .bss and .data sections in RAM, respectively.
The AT > FLASH directive places the actual contents of the .data section
in the FLASH memory region (which needs to be defined separately from this
linker script snippet). Then _sidata is set to the address of that data in
flash.
Note that while _sbss, _ebss, _sdata and _edata are Virtual Memory
Addresses (VMAs), _sidata is the Load Memory Address (LMA) of the .data
section.
On the Rust side, we must bind to those symbols using an extern block,
and can then call into this crate to perform RAM initialization:
unsafe fn before_main() { // The type, `u32`, indicates that the memory is 4-byte aligned extern "C" { static mut _sbss: u32; static mut _ebss: u32; static mut _sdata: u32; static mut _edata: u32; static _sidata: u32; } zero_bss(&mut _sbss, &mut _ebss); init_data(&mut _sdata, &mut _edata, &_sidata); }
Minimum Supported Rust Version (MSRV)
The MSRV of this release is Rust 1.31.0
Traits
| Word | Trait for machine word types. |
Functions
| init_data⚠ | Initializes the |
| zero_bss⚠ | Zeroes the |