From a8d7508006db8309550755a72719de83bde3cdd9 Mon Sep 17 00:00:00 2001
From: Sadeep Madurange <sadeep@asciimx.com>
Date: Fri, 5 Jun 2026 21:00:02 +0800
Subject: Improve writing.

---
 _log/arduino-due.md | 52 ++++++++++------------------------------------------
 1 file changed, 10 insertions(+), 42 deletions(-)

(limited to '_log/arduino-due.md')

diff --git a/_log/arduino-due.md b/_log/arduino-due.md
index 1330dbf..a55122c 100644
--- a/_log/arduino-due.md
+++ b/_log/arduino-due.md
@@ -4,21 +4,8 @@ date: 2024-09-16
 layout: post
 ---
 
-Three on-chip memories: ROM, flash0, flash1. ARM Cortex-M chips boot into
-0x00000. GPNVM bits map one of them to 0x00000: 
-
- - GPNVM1=0 → ROM (default).
- - GPNVM1=1 and GPNVM2=0 → flash0.
- - GPNVM1=1 and GPNVM2=1 → flash1.
-
-On power-up, control jumps to ROM. Without a user program, Atmel's SAM-BA
-bootloader traps execution in the ROM. Must remap memory via SWD to force chip
-to boot from flash, bypassing factory bootloader.
-
 Toolchain: ST-LINK/V2 programmer, OpenOCD, ARM GNU Compiler Toolchain.
 
-Connect ST-LINK/v2 to Arduino Due's DEBUG port:
-
 <table style="border: none; width: 100%;">
   <tr style="border: none;">
     <td style="border: none; width: 50%; vertical-align: top; background-color: transparent;">
@@ -32,7 +19,10 @@ Connect ST-LINK/v2 to Arduino Due's DEBUG port:
   </tr>
 </table>
 
-Remap memory using OpenOCD:
+ATSAM3X8E boots into 0x00000, which is mapped to ROM. ROM contains the SAM-BA
+bootloader.
+
+Remap start address to flash0 (flash driver section, OpenOCD manual AT91SAM3):
 
 ```
 $ openocd -f openocd-due.cfg
@@ -43,32 +33,8 @@ $ telnet localhost 4444
   > at91sam3 gpnvm show
 ```
 
-Full command list in OpenOCD manual AT91SAM3 (flash driver section).
-
-Initialize vector table with the stack pointer and the reset vector:
-
-```
-__attribute__((noreturn)) void _reset(void) 
-{
-    unsigned long *dst, *src;
-    extern unsigned long _sbss, _ebss;
-    extern unsigned long _sdata, _edata, _sidata;
-
-    for (dst = &_sbss; dst < &_ebss; dst++)
-        *dst = 0;
-    for (dst = &_sdata, src = &_sidata; dst < &_edata;)
-        *dst++ = *src++;
-
-    main();
-}
-
-extern const unsigned int _sp;
-
-__attribute__ ((section(".vtor"))) const void* _tab[] = { &_sp, _reset };
-```  
-
-Linker script: Place the vector table at the start of flash0 and initialize the
-stack pointer to the top of the RAM:
+Place the vector table at the start of flash0 and initialize the stack pointer
+to the top of the RAM:
 
 ```
 MEMORY
@@ -81,13 +47,15 @@ SECTIONS
 {
     .text :
     {
-        KEEP(*(.vtor))
+        KEEP(*(.vtor))  /* Vector table defined in main.c */
         *(.text*)
         *(.rodata*)
     } > rom
+
+    /* Data, bss sections */
 }
 
-_sp = ORIGIN(ram) + LENGTH(ram);
+_sp = ORIGIN(ram) + LENGTH(ram); /* Descending stack */
 ```
 
 Build and upload the program:
-- 
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