alfin K

Bare Metal C

2026-06-29T00:00:00+00:00

These are some notes for this topic based on these references:</p>

Bare Metal C</em> by Stephen Oualline</em> published by No Starch Press</em>.</li> </ul>
Basics#</a> </h2>
Arrays and Pointers #</a> </h3>
They are very simmilar but differ in terms of how they are declared:</p>
int array[5] = {1,2,3,4,5}; int* arrayPtr = array; // note we used array and not &array // array is already a ptr int i = array[1]; // is same as int i = *(arrayPtr + 1); </code></pre>Linker Models#</a> </h2> Ideal C Model#</a> </h3> There are 3 standard sections: text</code>, data</code>, bss</code>. text</code> is where read-only data go to. data</code> is the place for initialized data. bss</code> is for uninitialized data. Use size</code> to view each sections.</p> $ size example.o text data bss dec hex filename 481 4 4 489 1e9 example.o </code></pre> dec</code> is the total number and hex</code> is the total in hexadecimal. Those sections are allocated by the compiler. However there are two more sections stack</code> and heap</code> which is allocated by the linker.</p> GCC flags#</a> </h3> -Wall -Wextra * : To print warning messages for code that is correct but questionable.</p> </li> -Wa, <ASM_FLAGS> * : Pass flags that follow to assembler</p> </li> -Wl, <LD_FLAGS> * : Pass flags that follow to the linker</p> </li> </ul> Bit Twidling#</a> </h2> PORTD = (1 << 3) // sets the 3rd bit to 1 PORTD |= (1 << 3) // sets the 3rd bit to 1 keeping rest of them same PORTD |= (1 << 3) | (1 << 5) // set multiple bits; // keeping the rest of them same PORTD &= ~(1 << 3) // unset a bit; keeping others same PORTD &= ~((1 << 3) | (1 << 5)) // unset multiple bits; // keeps rest of them same </code></pre> Select Problems#</a> </h2> Chapter 4</em> :</em> Extracting bits 2 and 3 from an 8 bit register</p> uint8_t parity = (IO_REG >> 2) & 0x03 </code></pre>

Learning about USB protocol with a RISC-V board 2026-06-22T00:00:00+00:00 I stumbled upon this project called rv003usb[1]</a> by cnlohr. It features a bit-banged USB controller for the RISC-V CH32V003 MCU. I was always interested in learning more about the protocol and since I have a lot of free time due to sem breaks I will try to play around with this software. This article will document interesting things I find in the process for future reference.</p> [1]</a> https://github.com/cnlohr/rv003usb</code></p> Hardware#</a> </h2> I got a CH32V006 dev board and its programmer WCH.linkE from WeActStudios on aliexpress. They have schematics uploaded on their github page, which shows some interesting connections related to this rv003usb project. Maybe the board supports programming directly using the on-board USB-C by first flashing the bootloader USB bit-banged code. I will have to verify it later.</p> Software Stack#</a> </h2> So cnlohr has a nice repo with a lot of built in functionality [2]</a>. This project is an attempt to decouple essential functionality from the official IDE, so that a lightweight toolchain is available for these boards. However I still need the RISC-V GCC compiler in my system. I use Gentoo, here is how I set it up using crossdev:</p> Gentoo riscv toolchain installation#</a> </h3> To start development we need the riscv 32bit bare metal toolchain which has the assembler, compiler, linker and a glibc</code> replacement called newlib</code>. We probably won't need to use newlib</code> since ch32fun provides a lot of functionality out of the box. We need to first emerge sys-devel/crossdev</code> if not already installed. To configure crossdev refer the wiki as it gives multiple options.</p> Note: crossdev is a collection of scripts which can generate e-builds for portage to build cross-development toolchains. (Handles all the symlinking to your system GCC and all that stuff)</em></p> Now that crossdev is configured we can compile our toolchain using a single command:</p> crossdev --target riscv32-unknown-none-newlib // this next command is equivalent but your binary name will be different and // shorter for example: your gcc will now be riscv32-unknown-elf-gcc instead // of riscv32-unknown-none-newlib-gcc crossdev --target riscv32-unknown-elf // command to uninstall in case of errors; read gentoo wiki for more details crossdev --clean --target <target> </code></pre> WCH.LINK-E programmer setup and tips#</a> </h3> Trying out Typst 2026-06-17T00:00:00+00:00 Typst is an open source typesetting language. I am looking into it because it is said to be much easier than Latex. I have used Latex before, but because I don't use it often, I end up spending more time reading package documentations than writing.</p> As of writing this, I am on Gentoo. So, installing Typst was easy since it is packaged in the GURU repository. This is already very nice compared to installing a huge Latex meta package. From what I learned so far all you need is a single command to get a PDF.</p> typst compile <file> <output> </code></pre> Functions#</a> </h2> Looks like everything is a function in Typst and you pass in the required arguments. Some functions also accept a special argument called content</em> like #text</code> and #heading</code>. Functions which are frequenctly used often have synax sugars. I found a nice list of templates in this github repository [1]</a> which can be good starting place to learn more about the language.</p> [1]</a> https://github.com/qjcg/awesome-typst</code></p> Useful#</a> </h2> In the remaining section of this document I will put some code snippets which I find interesting and useful.</p> FreeBSD desktop issues 2026-05-18T00:00:00+00:00 I was playing around with FreeBSD 15 and was planning on daily driving it until some major issues started popping up.</p> WiFi#</a> </h2> My card is not supported currently but I heard drivers are on the way. So I had to use a package called wifibox</code> which spins up a headless Alpine Linux on the built-in bhyve</code> virtualisation tool. It exposes sockets to control the wpa_supplicant</code> on the guest machine to the host machine using socat. It worked really well. I have no issues with it.</p> Graphics#</a> </h2> The real issue was with graphics. I have an all AMD machine meaning my CPU, iGPU, dGPU all of them are AMD. So drivers should never be an issue. I set up amdgpu</code> and xorg</code>. For some reason my primary GPU was always the dGPU. When I forced xorg</code> to change primary to iGPU it would boot to a black screen. Not sure why this happens but if i were to guess it would be that the kernel finds the dGPU first since its at CPI:3:0:0 (iGPU is at 7:0:0) and flips the mux that way since my laptop is set to hybrid mode.</p> The main reason I decided not to daily drive FreeBSD was because some packages install nvidea-drivers</code> as dependencies. Now that itself is not an issue. but when these drivers are installed it replaces the mesa libglx.so.0</code> library in the modules directory of xorg</code> with nvidia versions of it. So now my glxinfo</code> gives me "cannot load glx module"</code> errors. There is no blocklist for pkg</code> through which I can ban all things related to nvidia. So now I have to do some hacky fix to get my graphics pipeline working praying that an update does not break it.</p> Title 2000-01-21T00:00:00+00:00 // Content</p> Example of elements 2000-01-01T00:00:00+00:00 h2 Heading#</a> </h2> h3 Heading#</a> </h3> h4 Heading#</a> </h4> h5 Heading#</a> </h5> h6 Heading#</a> </h6> Horizontal Rules#</a> </h2> Emphasis#</a> </h2> This is bold text</strong></p> This is bold text</strong></p> This is italic text</em></p> This is italic text</em></p> Strikethrough</del></p> Blockquotes#</a> </h2> Blockquotes can also be nested...</p> ...by using additional greater-than signs right next to each other...</p> ...or with spaces between arrows.</p> </blockquote> </blockquote> </blockquote> Lists#</a> </h2> Unordered</p> Create a list by starting a line with +</code>, -</code>, or *</code></li> Sub-lists are made by indenting 2 spaces: Facilisis in pretium nisl aliquet Nulla volutpat aliquam velit</li> </ul> </li> </ul> </li> Very easy!</li> </ul> Ordered</p> Lorem ipsum dolor sit amet</p> </li> Consectetur adipiscing elit</p> </li> Integer molestie lorem at massa</p> </li> You can use sequential numbers...</p> </li> ...or keep all the numbers as 1.</code></p> </li> </ol> Start numbering with offset:</p> foo</li> bar</li> </ol> Code#</a> </h2> Inline code</code></p> Indented code</p> // Some comments line 1 of code line 2 of code line 3 of code </code></pre> Block code "fences"</p> Sample text here... </code></pre> Tables#</a> </h2> Option</th> Description</th></tr></thead> data</td> path to data files to supply the data that will be passed into templates.</td></tr> engine</td> engine to be used for processing templates. Handlebars is the default.</td></tr> ext</td> extension to be used for dest files. extension to be used for dest files. extension to be used for dest files. extension to be used for dest files.</td></tr> </tbody></table> Right aligned columns</p> Option</th> Description</th></tr></thead> data</td> path to data files to supply the data that will be passed into templates.</td></tr> engine</td> engine to be used for processing templates. Handlebars is the default.</td></tr> ext</td> extension to be used for dest files.</td></tr> </tbody></table> Links#</a> </h2> link text</a></p> link with title</a></p> Images#</a> </h2> </p> </p> Like links, Images also have a footnote style syntax</p> </p> With a reference later in the document defining the URL location:</p> [id]: https://images.metmuseum.org/CRDImages/cl/original/DP101128.jpg "The Unicorn is Attacked" </code></pre> Footnotes</a>#</a> </h3> Footnote 1 link1</a></sup>.</p> Footnote 2 link2</a></sup>.</p> Duplicated footnote reference2</a></sup>.</p> ^{1</sup> Footnote can have markup</strong></p> </div> and multiple paragraphs.</p> ^{2</sup> Footnote text.</p> </div>}}

Select Problems #</a> </h2>
Chapter 4</em> :</em> Extracting bits 2 and 3 from an 8 bit register</p>
`uint8_t parity = (IO_REG >> 2) & 0x03 </code></pre>`

WCH.LINK-E programmer setup and tips #</a> </h3>

`Useful#</a> </h2> In the remaining section of this document I will put some code snippets which I find interesting and useful.</p>`

Links#</a> </h2>
link text</a></p>
link with title</a></p>

Footnotes</a>#</a> </h3>
Footnote 1 link 1</a></sup>.</p>
Footnote 2 link 2</a></sup>.</p>
Duplicated footnote reference 2</a></sup>.</p>
^{1</sup>
Footnote can have markup</strong></p>
</div>
and multiple paragraphs.</p>
^{2</sup>
Footnote text.</p>
</div>}}

alfin K

Bare Metal C

Learning about USB protocol with a RISC-V board

Trying out Typst

FreeBSD desktop issues

Title

Example of elements