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diff --git a/_site/log/arduino-due/index.html b/_site/log/arduino-due/index.html index d2248bc..0916c6f 100644 --- a/_site/log/arduino-due/index.html +++ b/_site/log/arduino-due/index.html @@ -2,12 +2,12 @@ <html> <head> <meta charset="utf-8"> - <title>How to set up ATSAM3X8E microcontrollers for bare-metal programming in C</title> + <title>ATSAM3X8E bare-metal programming</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> + <title>ATSAM3X8E bare-metal programming</title> <link rel="stylesheet" href="/assets/css/main.css"> <link rel="stylesheet" href="/assets/css/skeleton.css"> </head> @@ -41,38 +41,27 @@ <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> + <h2 class="center" id="title">ATSAM3X8E BARE-METAL PROGRAMMING</h2> <h6 class="center">16 SEPTEMBER 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> + <div class="twocol justify"><p>Notes on programming ATSAM3X8E chips (Arduino Due) without bootloader. Tested +on OpenBSD.</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>Need to bypass embedded bootloader—requires hardware programmer that speaks +Serial Wire Debug (SWD). ST-LINK/V2 works as SWD-USB adapter.</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>OpenOCD translates commands to binary sequences the chip understands. Runs +telnet server on startup for issuing commands.</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> +<p>ARM GNU Compiler Toolchain for compiling C programs. Both OpenOCD and ARM +toolchain available on 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> +<p>Arduino Due exposes ATSAM3X8E’s SWD interface via DEBUG port. ST-LINK/V2 +connects there.</p> <table style="border: none; width: 100%;"> <tr style="border: none;"> @@ -90,11 +79,10 @@ from a PC to the MCU.</p> <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> +<h2 id="upload-procedure">Upload procedure</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> +<p>Sample LED blink program with OpenOCD config and linker scripts in tarball +below.</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 \ @@ -102,8 +90,7 @@ First, use the following command to build it:</p> -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> +<p>Upload:</p> <div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ openocd -f openocd-due.cfg $ telnet localhost 4444 @@ -114,45 +101,36 @@ $ telnet localhost 4444 $ 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> +<p>First command starts OpenOCD. Telnet session halts chip, checks GPNVM bit. If +unset (returns 0), set to 1 and verify. Final command uploads program. See +OpenOCD manual AT91SAM3 flash driver section for full command list.</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>ARM chips boot into address 0x00000. ATSAM3X8E has ROM and dual-banked flash +(flash0/flash1) at different addresses. GPNVM bits control which maps to +0x00000.</p> + +<p>GPNVM1 cleared (default): boots from ROM (Atmel SAM-BA bootloader). GPNVM1=1, +GPNVM2=0: flash0 (0x80000) maps to 0x00000. Both cleared: flash1 maps to +0x00000.</p> + +<p>Program goes in flash0, so set GPNVM1=1 to boot our code instead of 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-notes">Linker script notes</h2> -<h2 id="linker-script">Linker script</h2> +<p>Vector table must be at first flash address–mandatory for ARM chips unless +using VTOR register for relocation.</p> -<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>First vector table entry: stack pointer. Initialize to highest memory location +(ATSAM3X8E has descending stack).</p> -<p>The first entry of the vector table must be the stack pointer. The stack -pointer must be initialized to the highest memory location available to -accommodate the ATSAM3X8E’s descending stack.</p> +<p>Second entry: reset vector. Place initialization code here (zero memory, set +registers) before jumping to main().</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>Commit: +<a href="https://git.asciimx.com/bare-metal-arduino-due/commit/?id=318496925ca76668dd9d63c3d060376f489276f8">3184969</a></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> |