LPC2138/crt

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after reset

The 12kB boot block is mapped into 0x7d000. It's also visible at 0x7fff d000.

Bootloader checks for valid checksum of vectors, then hands off control to flash at 0x0, or start serial port shit.

arm exception vector locations

ok, so these fuckers can be remapped:

* boot loader mode (on start up), boot block vectors are mapped here
* user flash mode (from boot code), activated by BL, needs valid program sig and non-forced BL. non re-mapped vectors (== stays in flash, bottom)
* user ram mode (from program), user program can remap vectors to bottom of SRAM

The 64-byte block is remapped. So some handlers can fit there.

arm vectors

0x0	Reset
0x4	Undefined Instruction
0x8	Software Interrupt
0xc	Prefetch Abort
0x10	Data Abort
0x14	2's complement of checksum of vectors
0x18	IRQ
0x1c	FIQ

Crt.s looks like this<enscript lang=asm>

       .section .vectors
       .code 32
       .align 0

       .global _vectors

_vectors: .reset: b start .undefined: bl endless .swi: bl endless .prefetchabort: bl endless .dataabort: bl endless .checksum: .word 0x92ffffec /* hand calculated, grr */ .irq: bl endless .fiq: bl endless

endless:

       b       endless

start:

       /* setup sp */
       ldr     sp, =_ram_end

       bl      init
       bl      main

       b       endless

</enscript>

A mofo was also the linker script:<enscript lang=asm> MEMORY {

       FLASH (rx) :    ORIGIN = 0,             LENGTH = 512K
       RAM (rw) :      ORIGIN = 0x40000000,    LENGTH = 32K

}

ENTRY(_vectors)

/* http://sourceware.org/binutils/docs/ld/Output-Section-LMA.html */

_ram_end = ORIGIN(RAM) + LENGTH(RAM) - 4;

SECTIONS {

       .text :
       {
               *(.vectors)
               *(.text)
               *(.rodata)
               *(.rodata.*)
       } >FLASH

       _fldata = . ;
       .data : ALIGN(4)
       {
               _data = . ;
               *(.data)
               _edata = . ;
       } >RAM AT>FLASH

       .bss : ALIGN(4)
       {
               _bss = . ;
               *(.bss)
               *(COMMON)
               _ebss = . ;
       } >RAM

} </enscript>

But ok, it works now, and after crt, we can transfer more init to c code:<enscript lang=c>

1. include <types.h>
2. include <board.h>

extern u32 _fldata, _data, _edata, _bss, _ebss, _ram_end; void init() {

       u32 *src = &_fldata;
       u32 *dest = &_data;

       /* copy .data from flash */
       while (dest < &_edata)
               *dest++ = *src++;

       /* zero .bss */
       dest = &_bss;
       while (dest < &_ebss)
               *dest++ = 0;

       /* poison the rest of ram */
       while (dest < (u32*)&src-16)
               *dest++ = 0xcbababe;

       board_init();

} </enscript>

Hrm, code dumps are boring, but crt.s and linker script really took a while to make it work.