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//! Minimal startup / runtime for RISC-V CPU's //! //! # Minimum Supported Rust Version (MSRV) //! //! This crate is guaranteed to compile on stable Rust 1.31 and up. It *might* //! compile with older versions but that may change in any new patch release. //! Note that `riscv64imac-unknown-none-elf` and `riscv64gc-unknown-none-elf` targets //! are not supported on stable yet. //! //! # Features //! //! This crate provides //! //! - Before main initialization of the `.bss` and `.data` sections. //! //! - `#[entry]` to declare the entry point of the program //! - `#[pre_init]` to run code *before* `static` variables are initialized //! //! - A linker script that encodes the memory layout of a generic RISC-V //! microcontroller. This linker script is missing some information that must //! be supplied through a `memory.x` file (see example below). This file //! must be supplied using rustflags and listed *before* `link.x`. Arbitrary //! filename can be use instead of `memory.x`. //! //! - A `_sheap` symbol at whose address you can locate a heap. //! //! ``` text //! $ cargo new --bin app && cd $_ //! //! $ # add this crate as a dependency //! $ edit Cargo.toml && cat $_ //! [dependencies] //! riscv-rt = "0.6.0" //! panic-halt = "0.2.0" //! //! $ # memory layout of the device //! $ edit memory.x && cat $_ //! MEMORY //! { //! RAM : ORIGIN = 0x80000000, LENGTH = 16K //! FLASH : ORIGIN = 0x20000000, LENGTH = 16M //! } //! //! REGION_ALIAS("REGION_TEXT", FLASH); //! REGION_ALIAS("REGION_RODATA", FLASH); //! REGION_ALIAS("REGION_DATA", RAM); //! REGION_ALIAS("REGION_BSS", RAM); //! REGION_ALIAS("REGION_HEAP", RAM); //! REGION_ALIAS("REGION_STACK", RAM); //! //! $ edit src/main.rs && cat $_ //! ``` //! //! ``` ignore,no_run //! #![no_std] //! #![no_main] //! //! extern crate panic_halt; //! //! use riscv_rt::entry; //! //! // use `main` as the entry point of this application //! // `main` is not allowed to return //! #[entry] //! fn main() -> ! { //! // do something here //! loop { } //! } //! ``` //! //! ``` text //! $ mkdir .cargo && edit .cargo/config && cat $_ //! [target.riscv32imac-unknown-none-elf] //! rustflags = [ //! "-C", "link-arg=-Tmemory.x", //! "-C", "link-arg=-Tlink.x", //! ] //! //! [build] //! target = "riscv32imac-unknown-none-elf" //! $ edit build.rs && cat $_ //! ``` //! //! ``` ignore,no_run //! use std::env; //! use std::fs::File; //! use std::io::Write; //! use std::path::Path; //! //! /// Put the linker script somewhere the linker can find it. //! fn main() { //! let out_dir = env::var("OUT_DIR").expect("No out dir"); //! let dest_path = Path::new(&out_dir); //! let mut f = File::create(&dest_path.join("memory.x")) //! .expect("Could not create file"); //! //! f.write_all(include_bytes!("memory.x")) //! .expect("Could not write file"); //! //! println!("cargo:rustc-link-search={}", dest_path.display()); //! //! println!("cargo:rerun-if-changed=memory.x"); //! println!("cargo:rerun-if-changed=build.rs"); //! } //! ``` //! //! ``` text //! $ cargo build //! //! $ riscv32-unknown-elf-objdump -Cd $(find target -name app) | head //! //! Disassembly of section .text: //! //! 20000000 <_start>: //! 20000000: 800011b7 lui gp,0x80001 //! 20000004: 80018193 addi gp,gp,-2048 # 80000800 <_stack_start+0xffffc800> //! 20000008: 80004137 lui sp,0x80004 //! ``` //! //! # Symbol interfaces //! //! This crate makes heavy use of symbols, linker sections and linker scripts to //! provide most of its functionality. Below are described the main symbol //! interfaces. //! //! ## `memory.x` //! //! This file supplies the information about the device to the linker. //! //! ### `MEMORY` //! //! The main information that this file must provide is the memory layout of //! the device in the form of the `MEMORY` command. The command is documented //! [here][2], but at a minimum you'll want to create at least one memory region. //! //! [2]: https://sourceware.org/binutils/docs/ld/MEMORY.html //! //! To support different relocation models (RAM-only, FLASH+RAM) multiple regions are used: //! //! - `REGION_TEXT` - for `.init`, `.trap` and `.text` sections //! - `REGION_RODATA` - for `.rodata` section and storing initial values for `.data` section //! - `REGION_DATA` - for `.data` section //! - `REGION_BSS` - for `.bss` section //! - `REGION_HEAP` - for the heap area //! - `REGION_STACK` - for hart stacks //! //! Specific aliases for these regions must be defined in `memory.x` file (see example below). //! //! ### `_stext` //! //! This symbol provides the loading address of `.text` section. This value can be changed //! to override the loading address of the firmware (for example, in case of bootloader present). //! //! If omitted this symbol value will default to `ORIGIN(REGION_TEXT)`. //! //! ### `_stack_start` //! //! This symbol provides the address at which the call stack will be allocated. //! The call stack grows downwards so this address is usually set to the highest //! valid RAM address plus one (this *is* an invalid address but the processor //! will decrement the stack pointer *before* using its value as an address). //! //! In case of multiple harts present, this address defines the initial stack pointer for hart 0. //! Stack pointer for hart `N` is calculated as `_stack_start - N * _hart_stack_size`. //! //! If omitted this symbol value will default to `ORIGIN(REGION_STACK) + LENGTH(REGION_STACK)`. //! //! #### Example //! //! Allocating the call stack on a different RAM region. //! //! ``` text //! MEMORY //! { //! L2_LIM : ORIGIN = 0x08000000, LENGTH = 1M //! RAM : ORIGIN = 0x80000000, LENGTH = 16K //! FLASH : ORIGIN = 0x20000000, LENGTH = 16M //! } //! //! REGION_ALIAS("REGION_TEXT", FLASH); //! REGION_ALIAS("REGION_RODATA", FLASH); //! REGION_ALIAS("REGION_DATA", RAM); //! REGION_ALIAS("REGION_BSS", RAM); //! REGION_ALIAS("REGION_HEAP", RAM); //! REGION_ALIAS("REGION_STACK", L2_LIM); //! //! _stack_start = ORIGIN(L2_LIM) + LENGTH(L2_LIM); //! ``` //! //! ### `_max_hart_id` //! //! This symbol defines the maximum hart id suppoted. All harts with id //! greater than `_max_hart_id` will be redirected to `abort()`. //! //! This symbol is supposed to be redefined in platform support crates for //! multi-core targets. //! //! If omitted this symbol value will default to 0 (single core). //! //! ### `_hart_stack_size` //! //! This symbol defines stack area size for *one* hart. //! //! If omitted this symbol value will default to 2K. //! //! ### `_heap_size` //! //! This symbol provides the size of a heap region. The default value is 0. You can set `_heap_size` //! to a non-zero value if you are planning to use heap allocations. //! //! ### `_sheap` //! //! This symbol is located in RAM right after the `.bss` and `.data` sections. //! You can use the address of this symbol as the start address of a heap //! region. This symbol is 4 byte aligned so that address will be a multiple of 4. //! //! #### Example //! //! ``` no_run //! extern crate some_allocator; //! //! extern "C" { //! static _sheap: u8; //! static _heap_size: u8; //! } //! //! fn main() { //! unsafe { //! let heap_bottom = &_sheap as *const u8 as usize; //! let heap_size = &_heap_size as *const u8 as usize; //! some_allocator::initialize(heap_bottom, heap_size); //! } //! } //! ``` //! //! ### `_mp_hook` //! //! This function is called from all the harts and must return true only for one hart, //! which will perform memory initialization. For other harts it must return false //! and implement wake-up in platform-dependent way (e.g. after waiting for a user interrupt). //! //! This function can be redefined in the following way: //! //! ``` no_run //! #[export_name = "_mp_hook"] //! pub extern "Rust" fn mp_hook() -> bool { //! // ... //! } //! ``` //! //! Default implementation of this function wakes hart 0 and busy-loops all the other harts. // NOTE: Adapted from cortex-m/src/lib.rs #![no_std] #![deny(missing_docs)] #![deny(warnings)] extern crate riscv; extern crate riscv_rt_macros as macros; extern crate r0; pub use macros::{entry, pre_init}; use riscv::register::mstatus; #[export_name = "error: riscv-rt appears more than once in the dependency graph"] #[doc(hidden)] pub static __ONCE__: () = (); extern "C" { // Boundaries of the .bss section static mut _ebss: u32; static mut _sbss: u32; // Boundaries of the .data section static mut _edata: u32; static mut _sdata: u32; // Initial values of the .data section (stored in Flash) static _sidata: u32; } /// Rust entry point (_start_rust) /// /// Zeros bss section, initializes data section and calls main. This function /// never returns. #[link_section = ".init.rust"] #[export_name = "_start_rust"] pub unsafe extern "C" fn start_rust() -> ! { extern "Rust" { // This symbol will be provided by the user via `#[entry]` fn main() -> !; // This symbol will be provided by the user via `#[pre_init]` fn __pre_init(); fn _mp_hook() -> bool; } if _mp_hook() { __pre_init(); r0::zero_bss(&mut _sbss, &mut _ebss); r0::init_data(&mut _sdata, &mut _edata, &_sidata); } // TODO: Enable FPU when available main(); } /// Trap entry point rust (_start_trap_rust) /// /// mcause is read to determine the cause of the trap. XLEN-1 bit indicates /// if it's an interrupt or an exception. The result is converted to an element /// of the Interrupt or Exception enum and passed to handle_interrupt or /// handle_exception. #[link_section = ".trap.rust"] #[export_name = "_start_trap_rust"] pub extern "C" fn start_trap_rust() { extern "C" { fn trap_handler(); } unsafe { // dispatch trap to handler trap_handler(); // mstatus, remain in M-mode after mret mstatus::set_mpp(mstatus::MPP::Machine); } } #[doc(hidden)] #[no_mangle] pub fn default_trap_handler() {} #[doc(hidden)] #[no_mangle] pub unsafe extern "Rust" fn default_pre_init() {} #[doc(hidden)] #[no_mangle] pub extern "Rust" fn default_mp_hook() -> bool { use riscv::register::mhartid; match mhartid::read() { 0 => true, _ => loop { unsafe { riscv::asm::wfi() } }, } }