pw_boot_cortex_m/public/pw_boot_cortex_m/boot.h

// Copyright 2020 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once

// This module is similar to a traditional assembly startup file paired with a
// linker script. It turns out that everything typically done in ARMv7-M
// assembly startup can be done straight from C code. This makes startup code
// easier to maintain, modify, and read.
//
// Core initialization is comprised of two primary parts:
//
// 1. Load boot information from ARMv7-M Vector Table: The ARMv7-M vector table
//    (See ARMv7-M Architecture Reference Manual DDI 0403E.b section B1.5)
//    dictates the starting Program Counter (PC) and Stack Pointer (SP) when the
//    SoC powers on. The vector table also contains a number of other vectors to
//    handle different exceptions. This module does not provide a vector table,
//    but it does account for it in the linker script.
//
// 2. Initialize static memory: When execution begins due to SoC power-on (or
//    the device is reset), static memory regions must be initialized to ensure
//    they contains the expected values when code begins to run. The SoC doesn't
//    inherently have a notion of how to do this, so before ANYTHING else the
//    memory must be initialized. This is done at the beginning of
//    pw_boot_Entry().
//
//
// The simple flow is as follows:
//   Power on -> PC and SP set (from vector_table by SoC) -> pw_boot_Entry()
//
// In pw_boot_Entry():
//   Initialize memory -> pw_PreMainInit() -> main()

#include <stdint.h>

#include "pw_preprocessor/compiler.h"
#include "pw_preprocessor/util.h"

PW_EXTERN_C_START

// The following extern symbols are provided by the linker script, and their
// values are accessible via the reference of the symbol.
//
// Example:
//   if (stack_pointer < &pw_boot_stack_low_addr) {
//     PW_LOG_ERROR("Main stack overflowed!")
//   }

// pw_boot_stack_[low/high]_addr indicate the range of the main stack. Note that
// this might not be the only stack in the system.
//
// The main stack pointer (sp_main) should be initialized to
// pw_boot_stack_high_addr. This can be done by inserting the address into index
// 0 of the ARMv7-M vector table. (See ARMv7-M Architecture Reference Manual DDI
// 0403E.b section B1.5.3)
extern uint8_t pw_boot_stack_low_addr;
extern uint8_t pw_boot_stack_high_addr;

// pw_boot_heap_[low/high]_addr indicate the address range reserved for the
// heap.
extern uint8_t pw_boot_heap_low_addr;
extern uint8_t pw_boot_heap_high_addr;

// The address that denotes the beginning of the .vector_table section. This
// can be used to set VTOR (vector table offset register) by the bootloader.
extern uint8_t pw_boot_vector_table_addr;

PW_EXTERN_C_END