| // 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_BootEntry(). |
| // |
| // |
| // The simple flow is as follows: |
| // Power on -> PC and SP set (from vector_table by SoC) -> pw_BootEntry() |
| // |
| // In pw_BootEntry(): |
| // 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_stack_low_addr) { |
| // PW_LOG_ERROR("Main stack overflowed!") |
| // } |
| |
| // pw_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_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_stack_low_addr; |
| extern uint8_t pw_stack_high_addr; |
| |
| // pw_heap_[low/high]_addr indicate the address range reserved for the heap. |
| extern uint8_t pw_heap_low_addr; |
| extern uint8_t pw_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_vector_table_addr; |
| |
| // Forward declaration of main. Pigweed applications are expected to implement |
| // this function. An implementation of main() is NOT provided by this module. |
| int main(); |
| |
| // For this module to work as expected, index 1 of the ARMv7-M vector table |
| // (which usually points to Reset_Handler) must be set to point to this |
| // function. This function is implemented by pw_boot_armv7m, and does early |
| // memory initialization. |
| PW_NO_PROLOGUE void pw_BootEntry(); |
| |
| // This function is called just after zero initialization of RAM and loading |
| // values into static memory (commonly labeled as the .data section in an ELF |
| // file). Per the naming, this function is called just before C++ static |
| // constructors are initialized. It is safe to run C code, but NOT safe to call |
| // out to any C++ code. |
| void pw_PreStaticConstructorInit(); |
| |
| // This function is called by pw_BootEntry() after memory initialization but |
| // before main. This allows targets to have pre-main initialization of the |
| // device and seamlessly swap out the main() implementation. This function is |
| // NOT implemented by pw_boot_armv7m. |
| void pw_PreMainInit(); |
| |
| PW_EXTERN_C_END |