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//! Minimal startup / runtime for RISC-V Fomu CPU //! //! # 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. //! //! # 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] //! fomu-rt = "0.0.1" //! panic-halt = "0.2.0" //! //! $ edit src/main.rs && cat $_ //! ``` //! //! ``` ignore,no_run //! #![no_std] //! #![no_main] //! //! extern crate panic_halt; //! //! use fomu_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.riscv32i-unknown-none-elf] //! rustflags = [ //! "-C", "link-arg=-Tlink.x", //! ] //! //! [build] //! target = "riscv32i-unknown-none-elf" //! $ //! ``` //! //! ``` 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. //! //! #### 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 vexriscv; 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: fomu-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); } 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() } }, } }