SAM4S bootloader not running application - arm

Question

I am trying to develop a custom bootloader for the Atmel SAM4S, but am not meeting with much success.
I have seen a few other posts on forums around this issue, but having tried solutions from each post I have found, it's time for my own post.
So far my bootloader receives data over UART, and writes it into flash, starting at address 0x00410000, however it fails to launch my program as expected.
Written based on numerous forum posts and also the Atmel bootloader example, this is my jumpToApp function:
void jumpToApp(void)
{
uint32_t loop;
// // Disable IRQ
Disable_global_interrupt();
__disable_irq();
// Disable system timer
SysTick->CTRL = 0;
// //Disable IRQs
for (loop = 0; loop < 8; loop++)
{
NVIC->ICER[loop] = 0xFFFFFFFF;
}
// Clear pending IRQs
for (loop = 0; loop < 8; loop++)
{
NVIC->ICPR[loop] = 0xFFFFFFFF;
}
// -- Modify vector table location
// Barriers
__DSB();
__ISB();
// Change the vector table
SCB->VTOR = ((uint32_t)FLASH_APP_START_ADDR & SCB_VTOR_TBLOFF_Msk);
// Barriers
__DSB();
__ISB();
// -- Enable interrupts
__enable_irq();
// -- Execute application
//------------------------------------------
__asm volatile("movw r1, #0x4100 \n"
"mov.w r1, r1, lsl #8 \n"
"ldr r0, [r1, #4] \n"
"ldr sp, [r1] \n"
"blx r0"
);
}
I have also tried this C based approach:
uint32_t v=FLASH_APP_START_ADDR;
asm volatile ("ldr sp,[%0,#0]": "=r" (v) : "0" (v));
typedef int(*fn_prt_t)(void);
fn_prt_t main_prog;
main_prog = (fn_prt_t)(appStartAddress);
main_prog();
and this alternative:
__DSB();
__ISB();
__set_MSP(*(uint32_t *) FLASH_APP_START_ADDR);
/* Rebase the vector table base address */
SCB->VTOR = ((uint32_t) FLASH_APP_START_ADDR & SCB_VTOR_TBLOFF_Msk);
__DSB();
__ISB();
__enable_irq();
/* Jump to application Reset Handler in the application */
asm("bx %0"::"r"(appStartAddress));
All with the same results, which makes sense as they all do pretty much the same thing.
Debugging the flash sector, I can see that the initial stack pointer in the new vector table is 0x20003b50, and the reset vector address is 0x004104d5, which both seem reasonable.
Stepping through, when execution is meant to jump to my application, I can see that the Program Counter is sat at 0x004104D0, which is close to, but not the reset vector address it should be.
The Stack Pointer also appears to be slightly off, reading 0x20003B28 instead of 0x20003b50.
Dissassembly shows exectution sitting at :
004104D0 b #-4
and never moving away.
Given that I have tried so many variations on jumping to application in flash that seem to have worked for others, I am beginning to think its my flash data at fault.
It is taken directly from the Intel Hex file generated by Atmel Studio 7.0, compiled with the linker offset flag:
-Wl,--section-start=.text=0x00410000
I am new to bootloaders, and have reached the limits of my understanding of low level cpu execution to provide more observation than the above, so any help or observations would be greatly appreciated!