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| author | Sadeep Madurange <sadeep@asciimx.com> | 2025-12-08 17:34:35 +0800 |
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| committer | Sadeep Madurange <sadeep@asciimx.com> | 2025-12-08 21:05:19 +0800 |
| commit | 752a06ec0ebf20d6232b13f1ea53fe21fefcefbd (patch) | |
| tree | 690411afad8eb76216417a42de94135214cb2401 /_site/blog/arduino-due/index.html | |
| parent | 20b0a045a7dc78f9728837fe5a1be8cf12caae4e (diff) | |
| download | www-752a06ec0ebf20d6232b13f1ea53fe21fefcefbd.tar.gz | |
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diff --git a/_site/blog/arduino-due/index.html b/_site/blog/arduino-due/index.html new file mode 100644 index 0000000..fee442f --- /dev/null +++ b/_site/blog/arduino-due/index.html @@ -0,0 +1,172 @@ +<!DOCTYPE html> +<html> + <head> + <meta charset="utf-8"> + <title>How to set up ATSAM3X8E microcontrollers for bare-metal programming in C</title> + + <head> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <title>How to set up ATSAM3X8E microcontrollers for bare-metal programming in C</title> + <link rel="stylesheet" href="/assets/css/main.css"> + <link rel="stylesheet" href="/assets/css/skeleton.css"> +</head> + + + + </head> + <body> + + <div id="nav-container" class="container"> + <ul id="navlist" class="left"> + + <li > + <a href="/" class="link-decor-none">hme</a> + </li> + <li class="active"> + <a href="/blog/" class="link-decor-none">blg</a> + </li> + <li > + <a href="/projects/" class="link-decor-none">poc</a> + </li> + <li > + <a href="/about/" class="link-decor-none">abt</a> + </li> + <li><a href="/feed.xml" class="link-decor-none">rss</a></li> + </ul> +</div> + + + + <main> + <div class="container"> + <div class="container-2"> + <h2 class="center" id="title">HOW TO SET UP ATSAM3X8E MICROCONTROLLERS FOR BARE-METAL PROGRAMMING IN C</h2> + <h6 class="center">05 OCTOBER 2024</h5> + <br> + <div class="twocol justify"><p>This article is a step-by-step guide for programming bare-metal ATSAM3X8E chips +found on Arduino Due boards. It also includes notes on the chip’s memory layout +relevant for writing linker scripts. The steps described in this article were +tested on an OpenBSD workstation.</p> + +<h2 id="toolchain">Toolchain</h2> + +<p>To interact directly with a bare-metal ATSAM3X8E chips, we must bypass the +embedded bootloader. To do that, we need a hardware programmer capable of +communicating with the chip over the Serial Wire Debug (SWD) protocol. Since +the workstation we upload the program from presumably doesn’t speak SWD, the +hardware programmer acts as a SWD-USB adapter. The <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 fits this +bill.</p> + +<p>The <a href="https://openocd.org/" class="external" target="_blank" rel="noopener noreferrer">OpenOCD</a> on-chip debugger software supports +ATSAM3X8E chips. OpenOCD, on startup, runs a telnet server that we can connect to +to issue commands to the ATSAM3X8E chip. OpenOCD translates plain-text commands +into the binary sequences the chip understands, and sends them over the wire.</p> + +<p>Finally, we need the <a href="https://developer.arm.com/Tools%20and%20Software/GNU%20Toolchain" class="external" target="_blank" rel="noopener noreferrer">ARM GNU Compiler +Toolchain</a> to compile C programs for the chip. The ARM GNU compiler +toolchain and OpenOCD, as a consequence of being free software, are available +on every conceivable platform, including OpenBSD.</p> + +<h2 id="electrical-connections">Electrical connections</h2> + +<p>The following photos illustrate the electrical connections between the Arduino +Due, PC, and the ST-LINK/V2 programmer required to transfer 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 ATSAM3X8E’s SWD interface via its DEBUG port. The +ST-LINK/v2 programmer connects to that to communicate with the chip.</p> + +<h2 id="uploading-the-program">Uploading the program</h2> + +<p>The source.tar.gz tarball at the end of this page contains a sample C program +(the classic LED blink program) with OpenOCD configuration and linker scripts. +First, use the following command to build it:</p> + +<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> + +<p>Then, open a telnet session with OpenOCD and issue the following sequence of +commands to configure the chip and upload the compiled program to it:</p> + +<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ openocd -f openocd-due.cfg +$ telnet localhost 4444 + > halt + > at91sam3 gpnvm show + > at91sam3 gpnvm set 1 + > at91sam3 gpnvm show +$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit" +</code></pre></div></div> + +<p>The first of the above commands starts OpenOCD. In the telnet session, the +first command halts the chip in preparation for receiving commands. Next, we +inspect the current GPNVM bit setting (more on this later). If the bit is unset +(the gpnvm show command returns 0), we set it to 1 and verify the update.</p> + +<p>The final command, issued from outside the telnet session, uploads the program +to the chip. Those are the bare minimum set of commands required to program the +chip. The AT91SAM3 flash driver section of the OpenOCD manual lists all +available commands for the ATSAM3X8E chip.</p> + +<h2 id="gpnvm-bits">GPNVM bits</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. The GPNVM bits control which of them +maps to 0x00000. When GPNVM1 is cleared (the default), the chip boots from the ROM, +which contains Atmel’s SAM-BA bootloader.</p> + +<p>Conversely, 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 in the linker script, we set the +GPNVM1 bit and leave the GPNVM2 bit unchanged to ensure the chip +executes our program instead of the embedded bootloader at startup.</p> + +<h2 id="linker-script">Linker script</h2> + +<p>At a minimum, the linker script must place the vector table at the first +address of the flash. This is mandatory for ARM chips unless we relocate the +vector table using the VTOR register.</p> + +<p>The first entry of the vector table must be the stack pointer. The stack +pointer must be initializes to the highest memory location available to +accommodate the ATSAM3X8E’s descending stack.</p> + +<p>The second entry of the vector table must be the reset vector. In the reset +vector, we can perform tasks such as zeroing out memory and initializing +registers before passing control to the main program.</p> + +<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> +</div> + <p class="post-author right">by W. D. Sadeep Madurange</p> + </div> + </div> + </main> + + <div class="footer"> + <div class="container"> + <div class="twelve columns right container-2"> + <p id="footer-text">© ASCIIMX - 2025</p> + </div> + </div> +</div> + + + </body> +</html> |