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//! Minimal startup / runtime for PicoRV32 RISC-V CPU //! //! # Minimum Supported Rust Version (MSRV) //! //! This crate is guaranteed to compile on stable Rust 1.32 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 PicoRV32 RISC-V //! microcontroller. This linker script is missing some information that must //! be supplied through a `memory.x` file (see example below). //! //! - 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] //! picorv32-rt = "0.4.0" //! panic-halt = "0.2.0" //! //! $ # memory layout of the device //! $ edit memory.x && cat $_ //! MEMORY //! { //! /* NOTE K = KiBi = 1024 bytes */ //! FLASH : ORIGIN = 0x00100000, LENGTH = 0x400000 //! RAM : ORIGIN = 0x00000000, LENGTH = 0x3800 //! } //! //! $ edit src/main.rs && cat $_ //! ``` //! //! ``` ignore,no_run //! #![no_std] //! #![no_main] //! //! extern crate panic_halt; //! //! use picorv32::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.riscv32imc-unknown-none-elf] //! rustflags = [ //! "-C", "link-arg=-Tlink.x" //! ] //! //! [build] //! target = "riscv32imc-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 two memory regions: one //! for Flash memory and another for RAM. //! //! [2]: https://sourceware.org/binutils/docs/ld/MEMORY.html //! //! The program instructions (the `.text` section) will be stored in the memory //! region named FLASH, and the program `static` variables (the sections `.bss` //! and `.data`) will be allocated in the memory region named RAM. //! //! ### `_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). //! //! If omitted this symbol value will default to `ORIGIN(RAM) + LENGTH(RAM)`. //! //! #### Example //! //! Allocating the call stack on a different RAM region. //! //! ``` //! MEMORY //! { //! /* call stack will go here */ //! CCRAM : ORIGIN = 0x10000000, LENGTH = 8K //! FLASH : ORIGIN = 0x08000000, LENGTH = 256K //! /* static variables will go here */ //! RAM : ORIGIN = 0x20000000, LENGTH = 40K //! } //! //! _stack_start = ORIGIN(CCRAM) + LENGTH(CCRAM); //! ``` //! //! ### `_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 //! //! ``` //! 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); //! } //! } //! ``` //! //! ## `pre_init!` //! //! A user-defined function can be run at the start of the reset handler, before RAM is //! initialized. The macro `pre_init!` can be called to set the function to be run. The function is //! intended to perform actions that cannot wait the time it takes for RAM to be initialized, such //! as disabling a watchdog. As the function is called before RAM is initialized, any access of //! static variables will result in undefined behavior. // NOTE: Adapted from cortex-m/src/lib.rs #![no_std] #![deny(missing_docs)] #![deny(warnings)] extern crate riscv; extern crate picorv32_rt_macros as macros; extern crate r0; pub use macros::{entry, pre_init}; 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; // Address of _start_trap #[cfg(feature = "interrupts")] static _start_trap: 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(); } __pre_init(); r0::zero_bss(&mut _sbss, &mut _ebss); r0::init_data(&mut _sdata, &mut _edata, &_sidata); #[cfg(feature = "interrupts")] picorv32::interrupt::enable(); main(); } /// Trap entry point rust (_start_trap_rust) /// /// `irqs` is a bitmask off IRQs to handle #[link_section = ".trap.rust"] #[export_name = "_start_trap_rust"] pub extern "C" fn start_trap_rust(irqs: u32) { extern "C" { fn trap_handler(irqs: u32); } unsafe { // dispatch trap to handler trap_handler(irqs); } } /// Default Trap Handler #[no_mangle] pub fn default_trap_handler(_irqs: u32) {} #[doc(hidden)] #[no_mangle] pub unsafe extern "Rust" fn default_pre_init() {} /// Usage: /// /// ``` /// use core::sync::atomic; /// use core::sync::atomic::Ordering; /// /// pub fn timer() { /// // ... /// } /// /// pub fn illegal_instruction() { /// loop { /// atomic::compiler_fence(Ordering::SeqCst); /// } /// } /// /// pub fn bus_error() { /// loop { /// atomic::compiler_fence(Ordering::SeqCst); /// } /// } /// /// pub fn irq5() { /// // ... /// } /// /// pub fn irq6() { /// // ... /// } /// /// picorv32_interrupts!( /// 0: timer, /// 1: illegal_instruction, /// 2: bus_error, /// 5: irq5, /// 6: irq6 /// ); /// ``` #[cfg(feature = "interrupts")] #[macro_export] macro_rules! picorv32_interrupts { (@interrupt ($n:literal, $pending_irqs:expr, $handler:ident)) => { if $pending_irqs & (1 << $n) != 0 { $handler(); } }; ( $( $irq:literal : $handler:ident ),* ) => { #[no_mangle] pub extern "C" fn trap_handler(pending_irqs: u32) { $( picorv32_interrupts!(@interrupt($irq, pending_irqs, $handler)); )* } }; }