Arduino Due and Clang

pkg install bossa arm-none-eabi-gcc

pw group mod dialer -m <user>

cc -nostdlib -ffreestanding -target arm-none-eabi -march=armv7-m -Tlinker-script.ld -Wl,--entry=start blink.c -o blink.elf
arm-none-eabi-objcopy -O binary blink.elf blink.bin

cu -l /dev/cuaU0 -s 1200

bossac --write --verify -p /dev/cuaU0 --boot -R blink.bin

// This is the top of the stack, as provided to us by the linker.
extern unsigned int _estack;


// This is a partial definition of the vector table. It only defines the
// first two entries which, as far as I can tell, are the minimum needed
// for a program to work at all.
// Space for the other interrupt handlers is reserved. I'm not sure if this
// is necessary, but I can imagine that the vector table not having the
// right length could cause all kinds of problems (imagine if it was too
// short, and the linker would place something else directly after it).
typedef struct {
    void *initial_stack_pointer_value;
    void *reset_handler;

    char other_interrupt_vectors[44 * 4]; // space for 44 32-bit pointers
} VectorTable;


void start();


// The vector table. We're using GCC-specific functionality to place this
// into the .vectors section, not where it would normally go (I suppose
// .rodata). The linker script makes sure that the .vectors section is at
// the right place.
__attribute__ ((section(".vectors")))
const VectorTable vector_table = {
    (void *)(&_estack),
    (void *)start,
};



// Addresses of several registers used to control parallel I/O.
static volatile int * const pb_pio_enable          = (int *)0x400E1000;
static volatile int * const pb_output_enable       = (int *)0x400E1010;
static volatile int * const pb_set_output_data     = (int *)0x400E1030;
static volatile int * const pb_clear_output_data   = (int *)0x400E1034;

// Bit mask for PB27. This is pin 13 (the built-in LED) on the Arduino Due.
static const int pb27_mask = 0x08000000;

// Addresses of several registers used to control the real-time timer.
static volatile int * const timer_mode_register  = (int *)0x400E1A30;
static volatile int * const timer_value_register = (int *)0x400E1A38;


// As the name suggests, this function sleeps for a given number of
// milliseconds. Our replacement for Arduino's delay function.
void sleep_ms(int milliseconds) {
    int sleep_until = *timer_value_register + milliseconds;
    while (*timer_value_register < sleep_until) {}
}

// This function is the entry point for our application and the handler
// function for the reset interrupt.
void start() {
    // Enable PB27 (pin 13) and configure it for output.
    *pb_pio_enable    = pb27_mask;
    *pb_output_enable = pb27_mask;

    // Set the timer to a resolution of a millisecond.
    *timer_mode_register = 0x00000020;

    // Continuously set and clear output on PB27 (pin 13). This blinks
    // the Due's built-in LED, which is the single purpose of this
    // program.
    while (1) {
        *pb_set_output_data = pb27_mask;
        sleep_ms(200);
        *pb_clear_output_data = pb27_mask;
        sleep_ms(200);
    }
}

/* ----------------------------------------------------------------------------
 *         SAM Software Package License
 * ----------------------------------------------------------------------------
 * Copyright (c) 2012, Atmel Corporation
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following condition is met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the disclaimer below.
 *
 * Atmel's name may not be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * DISCLAIMER: THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
 * DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * ----------------------------------------------------------------------------
 */

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
SEARCH_DIR(.)

/* Memory Spaces Definitions */
MEMORY
{
    rom (rx)    : ORIGIN = 0x00080000, LENGTH = 0x00080000 /* Flash, 512K */
    sram0 (rwx) : ORIGIN = 0x20000000, LENGTH = 0x00010000 /* sram0, 64K */
    sram1 (rwx) : ORIGIN = 0x20080000, LENGTH = 0x00008000 /* sram1, 32K */
    ram (rwx)   : ORIGIN = 0x20070000, LENGTH = 0x00018000 /* sram, 96K */
}

/* Section Definitions */
SECTIONS
{
    .text :
    {
        . = ALIGN(4);
        _sfixed = .;
        KEEP(*(.vectors .vectors.*))
        *(.text .text.* .gnu.linkonce.t.*)
        *(.glue_7t) *(.glue_7)
        *(.rodata .rodata* .gnu.linkonce.r.*)
        *(.ARM.extab* .gnu.linkonce.armextab.*)

        /* Support C constructors, and C destructors in both user code
           and the C library. This also provides support for C++ code. */
        . = ALIGN(4);
        KEEP(*(.init))
        . = ALIGN(4);
        __preinit_array_start = .;
        KEEP (*(.preinit_array))
        __preinit_array_end = .;

        . = ALIGN(4);
        __init_array_start = .;
        KEEP (*(SORT(.init_array.*)))
        KEEP (*(.init_array))
        __init_array_end = .;

        . = ALIGN(0x4);
        KEEP (*crtbegin.o(.ctors))
        KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
        KEEP (*(SORT(.ctors.*)))
        KEEP (*crtend.o(.ctors))

        . = ALIGN(4);
        KEEP(*(.fini))

        . = ALIGN(4);
        __fini_array_start = .;
        KEEP (*(.fini_array))
        KEEP (*(SORT(.fini_array.*)))
        __fini_array_end = .;

        KEEP (*crtbegin.o(.dtors))
        KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
        KEEP (*(SORT(.dtors.*)))
        KEEP (*crtend.o(.dtors))

        . = ALIGN(4);
        _efixed = .;            /* End of text section */
    } > rom

    /* .ARM.exidx is sorted, so has to go in its own output section.  */
    PROVIDE_HIDDEN (__exidx_start = .);
    .ARM.exidx :
    {
      *(.ARM.exidx* .gnu.linkonce.armexidx.*)
    } > rom
    PROVIDE_HIDDEN (__exidx_end = .);

    . = ALIGN(4);
    _etext = .;

    .relocate : AT (_etext)
    {
        . = ALIGN(4);
        _srelocate = .;
        *(.ramfunc .ramfunc.*);
        *(.data .data.*);
        . = ALIGN(4);
        _erelocate = .;
    } > ram

    /* .bss section which is used for uninitialized data */
    .bss ALIGN(4) (NOLOAD) :
    {
        . = ALIGN(4);
        _sbss = . ;
        _szero = .;
        *(.bss .bss.*)
        *(COMMON)
        . = ALIGN(4);
        _ebss = . ;
        _ezero = .;
    } > ram

    . = ALIGN(4);
    _end = . ;

    /* .stack_dummy section doesn't contains any symbols. It is only
       used for linker to calculate size of stack sections, and assign
       values to stack symbols later */
    .stack_dummy :
    {
        *(.stack*)
    } > ram

    /* Set stack top to end of ram, and stack limit move down by
     * size of stack_dummy section */
    __StackTop = ORIGIN(ram) + LENGTH(ram);
    __StackLimit = __StackTop - SIZEOF(.stack_dummy);
    PROVIDE(_sstack = __StackLimit);
    PROVIDE(_estack = __StackTop);
}