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| author | Sadeep Madurange <sadeep@asciimx.com> | 2025-10-25 18:19:48 +0800 |
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| committer | Sadeep Madurange <sadeep@asciimx.com> | 2025-10-25 19:07:22 +0800 |
| commit | 8cd867cd53794386cb9443bfc023fe97c5c5fa47 (patch) | |
| tree | 0f3f076e8b7f542b511d737eaaf3f3ec1cef457d /_site/archive/arduino-due/index.html | |
| parent | 210a4c8671b368a3a240f9cb7a0bd1718a301523 (diff) | |
| download | www-8cd867cd53794386cb9443bfc023fe97c5c5fa47.tar.gz | |
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diff --git a/_site/archive/arduino-due/index.html b/_site/archive/arduino-due/index.html new file mode 100644 index 0000000..76baab0 --- /dev/null +++ b/_site/archive/arduino-due/index.html @@ -0,0 +1,158 @@ +<!DOCTYPE html> +<html> + <head> + <meta charset="utf-8"> + <title>Bare-metal ARM Cortex M3 chips</title> + <head> +<meta charset="utf-8"> + <title>Bare-metal ARM Cortex M3 chips</title> + <link rel="stylesheet" href="/assets/css/main.css"> + <link rel="stylesheet" href="/assets/css/normalize.css"> + <link rel="stylesheet" href="/assets/css/skeleton.css"> +</head> + + + </head> + <body> + + <div class="container"> + <ul id="navlist" class="left"> + + <li > + <a href="/">hme</a> + </li> + <li > + <a href="/projects/">proj</a> + </li> + <li > + <a href="/about/">abt</a> + </li> + <li><a href="/feed.xml">rss</a></li> + </ul> +</div> + + + + <main> + <div class="container"> + <h2 class="brand center" id="title">BARE-METAL ARM CORTEX M3 CHIPS</h2> + + <h6 class="center">05 OCTOBER 2024</h5> + + <br> + + <div class="threecol justify"><p>This post is about programming bare metal SAM3X8E Arm Cortex M3 chips found on +Arduino Due boards. I had to learn how to do this because none of the +high-level tools for programming Arduino Dues are available for OpenBSD, which +I use for much of my personal computing.</p> + +<h2 id="toolchain">Toolchain</h2> + +<p>Since we will not be using pre-packaged development tools, we need to assemble +our own toolchain. As usual, we need a compiler toolchain to build programs for +the target chip. As we will be bypassing the embedded bootloader, we will also +need a hardware programmer and an on-chip debugger to flash programs to the +chip. I used the following toolchain.</p> + +<ul> + <li><a href="https://developer.arm.com/Tools%20and%20Software/GNU%20Toolchain" class="external" target="_blank" rel="noopener noreferrer">Arm GNU compiler +toolchain</a>.</li> + <li><a href="https://openocd.org/" class="external" target="_blank" rel="noopener noreferrer">OpenOCD</a> on-chip debugger.</li> + <li><a href="https://www.st.com/en/development-tools/st-link-v2.html" class="external" target="_blank" rel="noopener noreferrer">ST-LINK/V2</a> +programmer.</li> +</ul> + +<h2 id="electrical-connections">Electrical connections</h2> + +<p>The following diagram outlines the electrical connections between the different +components necessary to move a compiled program from a PC to the MCU.</p> + +<table style="border: none; width: 100%;"> + <tr style="border: none;"> + <td style="border: none; width: 50%; vertical-align: top; background-color: transparent;"> + <img src="schematic.png" alt="Pinout" style="width: 100%" /> + <p style="text-align: center;">Wiring</p> + </td> + <td style="border: none; width: 50%; vertical-align: top; background-color: transparent;"> + <img src="connections.jpeg" alt="Circuit" style="width: 100%" /> + <p style="text-align: center;">Arduino Due</p> + </td> + </tr> +</table> + +<p>Arduino Due exposes the SAM3X8E’s Serial Wire Debug (SWD) interface via its +DEBUG port. The ST-LINK/v2 programmer uses the SWD protocol to communicate with +the chip.</p> + +<h2 id="uploading-the-program">Uploading the program</h2> + +<p>Follow the steps below to upload a program to the SAM3X8E chip. The +source.tar.gz tarball at the end of the page contains a sample program with a +OpenOCD config file and a linker script.</p> + +<ol> + <li>Start OpenOCD: + <div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ openocd -f openocd-due.cfg +</code></pre></div> </div> + </li> + <li> + <p>Open a telnet session and check that the GPNVM1 bit is set. Otherwise +set it to 1:</p> + + <div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ telnet localhost 4444 + > halt + > at91sam3 gpnvm show + > at91sam3 gpnvm set 1 + > at91sam3 gpnvm show +</code></pre></div> </div> + </li> + <li>Build the program using the custom linker script. + <div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \ + -nostartfiles \ + -nostdlib \ + -o a.elf main.c +</code></pre></div> </div> + </li> + <li>Upload the program using OpenOCD: + <div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit" +</code></pre></div> </div> + </li> +</ol> + +<p>Refer to the OpenOCD manual (AT91SAM3 flash driver section) for a complete list +of commands supported for the ATSAM3X8E.</p> + +<h2 id="gpnvm-bits-and-the-linker-script">GPNVM bits and the linker script</h2> + +<p>By design, ARM chips boot into address 0x00000. ATSAM3X8E’s memory consists of +a ROM and a dual-banked flash (flash0 and flash1), residing in different +locations of the chip’s address space.</p> + +<p>The GPNVM bits control which of them maps to 0x00000. When GPNVM1 is cleared +(default), the chip boots from the ROM, which contains Atmel’s SAM-BA +bootloader. So, the chip runs the embedded bootloader instead of our program.</p> + +<p>When the GPNVM1 bit is 1 (and the GPNVM2 bit is 0), flash0 at address 0x80000 +maps to 0x00000. When both GPNVM bits are 0, flash1 maps to 0x00000. Since we +place our program in flash0 using the linker script, we set the GPNVM1 bit and +leave the GPNVM2 bit as it is.</p> + +<p>The linker script places the vector table at the first address of the flash. +ARM chips expect this unless we relocate the vector table using the VTOR +register. The first entry of the vector table must be the stack pointer, and +the second must be the reset vector.</p> + +<p>Finally, the ATSAM3X8E uses a descending stack. So, in the linker script, we +initialize the stack pointer to the highest memory location available. In the +reset vector, we zero out memory, initialize registers, and perform other tasks +before passing control to the main program.</p> + +<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> +</div> + + <p class="right italics">by W. D. Sadeep Madurange</p> + </div> + </main> + + </body> +</html> |