Can't compile my code with arm-none-eabi-gcc to work, Beginner

It seems that writing 0xffffffff at 0x2fc disable this feature.

According the documentation linked above (page 5), you can define NO_CRP in you C code like this :

#define NO_CRP 0xFFFFFFFF
#define NO_ISP_MAGIC 0x4E697370
#define CRP1_MAGIC 0x12345678
#define CRP2_MAGIC 0x87654321
/**** DANGER CRP3 WILL LOCK PART TO ALL READS and WRITES ****/
/*********** #define CRP3_MAGIC xxxx 0x43218765 *************/

#define CURRENT_CRP_SETTING NO_CRP 

__attribute__  ((section(".crp"))) const uint32_t CRP_WORD = CURRENT_CRP_SETTING;

And the add this to your linker code :

ENTRY(ResetISR)

SECTIONS

{

  .text : 

  {

    KEEP(*(.isr_vector)) 

    . = 0x000002FC;

    KEEP(*(.crp))

    *(.text*) 

    *(.rodata*) 

   } > MFlash32

  ...

}

If you search for NO_CRP on Github, and select "Code" after submitting the search, you might find some working examples, like this.

It seems that writing 0xffffffff at 0x2fc disable this feature.

According the documentation linked above (page 5), you can define NO_CRP in you C code like this :

#define NO_CRP 0xFFFFFFFF
#define NO_ISP_MAGIC 0x4E697370
#define CRP1_MAGIC 0x12345678
#define CRP2_MAGIC 0x87654321
/**** DANGER CRP3 WILL LOCK PART TO ALL READS and WRITES ****/
/*********** #define CRP3_MAGIC xxxx 0x43218765 *************/

#define CURRENT_CRP_SETTING NO_CRP 

__attribute__  ((section(".crp"))) const uint32_t CRP_WORD = CURRENT_CRP_SETTING;

And the add this to your linker code :

ENTRY(ResetISR)

SECTIONS

{

  .text : 

  {

    KEEP(*(.isr_vector)) 

    . = 0x000002FC;

    KEEP(*(.crp))

    *(.text*) 

    *(.rodata*) 

   } > MFlash32

  ...

}

If you search for NO_CRP on Github, and select "Code" after submitting the search, you might find some working examples, like this.

While I don't have any recommendations for books on "how to create linker scripts", you might be interested by The Definitive Guide to ARM® CORTEX®-M3 and CORTEX®-M4 Processors (Third Edition).

When it comes to ARM programming, what helped me the most was building my first "Hello world" assembler script, that ran on an Android device through adb shell.

The Hello world script was :

.data

msg:
    .ascii      "Hello, ARM!\n"
len = . - msg


.text

.globl _start
_start:
    /* syscall write(int fd, const void *buf, size_t count) */
    mov    %r0, $1    /* fd -> stdout */
    ldr    %r1, =msg  /* buf -> msg */
    ldr    %r2, =len  /* count -> len(msg) */
    mov    %r7, $4    /* write is syscall #4 */
    svc    $0          /* invoke syscall */

    /* syscall exit(int status) */
    mov    %r0, $0    /* status -> 0 */
    mov    %r7, $1    /* exit is syscall #1 */
    svc    $0          /* invoke syscall */

And compiled like this :

armv7a-hardfloat-linux-gnueabi-as -o hello.o hello.s
armv7a-hardfloat-linux-gnueabi-ld -o hello hello.o
adb push hello /data/local/tmp
adb shell /data/local/tmp/hello

Hello, ARM!

Then, I searched for a list of Linux system calls numbers for ARM and began playing with the code.

I also learned how to execute ARM code directly on a virtual machine, using this tutorial : 3. Hello ARM . You're maybe searching for that kind of tutorials. QEMU allows you to use GDB to step on each instruction executed by the virtual machine, and check/change the registers between instructions.

I learned the ELF structure and ARM machine code format by creating a small ELF linker myself in ruby, using :

- ARM Architecture Reference Manual, from ARM. You can get it from the ARM website. The instruction encoding section is a gold mine to understand how the instructions can be encoded.

- Executable and Linking Format (ELF) Specification, in order to understand the architecture of ELF files.

- A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux

I didn't go very far (Never implemented a Global Offset Table/Procedure Linkage Table), but I learned enough to understand the architecture of ELF objects (headers and sections) and how calling procedures from external libraries and dlopen() worked, which demystified a LOT of things.