main.cpp

/*
 * Copyright (C) 2015-2017 Erin Tomson <erin@rgba.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

// This is the Modulo bootloader for attiny841 based devices.
// By default, the bootloader uses the following memory layout (but this
// can be changed by changing BL_SIZE in the Makefile):
//
//   0x0000 - 2 byte reset vector. Jumps to the bootloader section (0x1800)
//   0x17FE - 2 byte application trampoline. The bootloader will jump here when it exits.
//   0x1800 - 2048 byte bootloader
//
// The bootloader will write bytes 0x0002-0x17FD, protecting the reset
// vector, trampoline and bootloader code. The reset vector will be
// automatically copied into the trampoline area.
//
// To view the disassembled bootloader, run:
//  /cygdrive/c/Program\ Files\ \(x86\)/Atmel/Atmel\ Toolchain/AVR8\ GCC/Native/3.4.1061/avr8-gnu-toolchain/bin/avr-objdump.exe -d Release/bootloader-attiny.elf


#include "bootloader.h"
#include "SelfProgram.h"
#include "fault_handlers.hpp"
#include "uart.hpp"
#include <stdio.h>


#if !defined(FLASH_BASE)
// https://github.com/libopencm3/libopencm3-examples/issues/224
#define FLASH_BASE                      (0x08000000U)
#endif

void startApplication() __attribute__((__noreturn__));
void startApplication() {
	const uint32_t *application = (uint32_t*)(FLASH_BASE + FLASH_APP_OFFSET);
	const uint32_t top_of_stack = application[0];
	const uint32_t reset_vector = application[1];

	asm("msr msp, %0; bx %1;" : : "r"(top_of_stack), "r"(reset_vector));
	__builtin_unreachable();
}

int main() {

	#if defined(NEED_TRAMPOLINE)
	// Set this value here, to avoid gcc generating a lot of
	// overhead for running a constructor to set this value. It
	// cannot be inline at compiletime, since the value is not known
	// until link time.
	SelfProgram::trampolineStart = (uint16_t)&startApplication * 2;
	#endif // defined(NEED_TRAMPOLINE)

	// Uncomment this to allow the use of printf on pin PA1 (ATTiny)
	// or PA2 (stm32), TX only. See also usart.cpp. This needs a
	// bigger bootloader area.
	//uart_stdout_init();
	//printf("Hello\n");

	runBootloader();
	startApplication();
}