Improve e-reader write-up.term

1 files changed, 49 insertions, 45 deletions

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@@ -44,20 +44,21 @@
           <h2 class="center" id="title">PROTOTYPE E-READER</h2>
           <h6 class="center">24 OCTOBER 2023</h5>
           <br>
-          <div class="twocol justify"><p>This project features a prototype e-reader powered by a 7.5-inch <a href="https://www.waveshare.com/" class="external" target="_blank" rel="noopener noreferrer">Waveshare</a> e-paper display and an
-ESP-WROOM-32 development board.</p>
+          <div class="twocol justify"><p>This project features a prototype e-reader powered by an ESP-WROOM-32
+development board and a 7.5-inch <a href="https://www.waveshare.com/" class="external" target="_blank" rel="noopener noreferrer">Waveshare</a>
+e-paper display.</p>
 
 <video style="max-width:100%;" controls="" poster="thumb.png">
   <source src="ereader.mp4" type="video/mp4" />
 </video>
 
-<h4 id="overview">Overview</h4>
+<h2 id="overview">Overview</h2>
 
-<p>In 2017, during a short stint as a project manager, I was tasked with
-installing some e-paper displays in a car park. Not knowing how they worked, I
-remember marveling at their sight like a muggle witnessing magic. As someone
-who enjoys reading, I found e-paper to be a true innovation. This project was
-born out of that enduring curiosity and love of e-paper technology.</p>
+<p>In 2017, I was tasked with installing some e-paper displays in a car park. Not
+knowing how they worked, I remember marveling at their sight like a Muggle
+witnessing magic. As someone who enjoys reading, I found e-paper to be a true
+innovation. This project was born out of that enduring curiosity and love of
+e-paper technology.</p>
 
 <p>The prototype, while far from ready for daily use, has some nifty features that
 fellow hobbyists and tinkerers may find interesting. The reader can display
@@ -65,59 +66,62 @@ books of arbitrary sizes by streaming them over HTTP. It employs sleep modes to
 minimize power consumption when not in use and records the reading progress in
 the chip’s RTC memory.</p>
 
-<p>The biggest challenge when building an e-reader using an ESP32 board is its low
-memory and lack of storage. My ESP-WROOM-32 board has 512 KB of SRAM and 4 MB
-of flash memory, which the freeRTOS, ESP-IDF, and my own program have to share.
-To put things into perspective, compare that to a Kindle Paperwhite, which has
+<p>The most formidable challenge when trying to build an e-reader with an ESP32
+board is its limited memory and storage. My ESP-WROOM-32 board has 512 KB of
+SRAM and 4 MB of flash memory, which the freeRTOS, ESP-IDF, and the e-reader
+application must share. To put things into perspective, a Kindle Paperwhite has
 at least 256 MB of memory and 8 GB of storage.</p>
 
-<p>Despite its constraints, as microcontrollers go, ESP32 is a powerful
-system-on-a-chip with a 160 MHz dual-core processor and integrated WiFi. So, I
-thought it’d be amusing to embrace the constraints and build my e-reader using
-just a $5 MCU and the power of C programming.</p>
+<p>Despite its size, as microcontrollers go, ESP32 is a powerful system-on-a-chip
+with a 160 MHz dual-core processor and integrated WiFi. So, I thought it’d be
+amusing to embrace the constraints and build my e-reader using a $5 MCU and the
+power of C programming.</p>
 
-<h4 id="the-file-format">The file format</h4>
+<h2 id="the-file-format">The file format</h2>
 
 <p>The file format dictates the complexity of the embedded software. So, I’ll
 begin there. The e-reader works by downloading and rendering a rasterized
 monochrome image of a page (a .ebm file).</p>
 
-<p>The EBM file contains a series of bitmaps, where each bitmap corresponds to a
-page of a book sized to fit the e-paper display. Each byte contains information
-for rendering eight pixels. For my display, which has a resolution of 480x800,
-the bitmaps are laid out along 48 KB boundaries. This simple file format lends
-well to HTTP streaming, which is its main advantage, as we will soon see.</p>
+<p>The EBM file contains a series of bitmaps, one for each page of the book. The
+dimensions of each bitmap are equal to the size of the display. Each byte of
+the bitmap encodes information for rendering eight pixels. For my display,
+which has a resolution of 480x800, the bitmaps are laid out along 48 KB
+boundaries. This simple file format lends well to HTTP streaming, which is its
+main advantage, as we will soon see.</p>
 
-<p>The enclosed pdftoebm.py script in the tarball at the end of the page converts
-PDF documents to an EBM file. I use it to make EBM files before uploading them
-to a web server.</p>
+<p>The pdftoebm.py script enclosed in the tarball at the end of the page converts
+PDF documents to EBM files.</p>
 
-<h4 id="how-does-it-work">How does it work?</h4>
+<h2 id="how-does-it-work">How does it work?</h2>
 
 <p>As the e-reader has no storage, it can’t store books locally. Instead, I first
-have to upload the EBM file I want to read to a web server. The location of the
-file is configured via the <code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code> setting in the Kconfig.projbuild
-file. To read a different book, I create an EBM file with the same name and
-upload it to the original location. That way, I don’t have to recompile the
-embedded software.</p>
+have to upload the EBM file I want to read to a web server. The <code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code>
+setting in the Kconfig.projbuild file points to the URL of the file. To read a
+different book, I create an EBM file with the same name and upload it to the
+original location. That way, I don’t have to modify the <code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code> value,
+which requires recompiling the embedded software.</p>
 
 <p>Upon powering up, the e-reader checks the reading progress stored in the RTC
 memory. It then downloads three pages (current, previous, and next) to a
 circular buffer in DMA-capable memory. When the user turns a page, one of the
-two cores of the MCU transfers it from the buffer to the display over a Serial
-Peripheral Interface (SPI). The other downloads a new page in the background. I
-use the ESP-IDF task API to pin the two routines to each core.</p>
-
-<p>I designed the EBM format with HTTP streaming in mind. To download a page based
-on the current reading progress, the e-reader specifies the page offset and the
-chunk size using the HTTP Range header.</p>
-
-<h4 id="afterword">Afterword</h4>
-
-<p>It’s been six years since the car park and the displays. At the time, I knew
-nothing about embedded systems or display drivers. It took a long time to
-develop the skill set, but now, at last, I know how those displays worked and
-how to build my own.</p>
+microprocessor’s two cores transfers it from the buffer to the display over a
+Serial Peripheral Interface (SPI). The other downloads a new page in the
+background. I use the ESP-IDF task API to distribute the two tasks between the
+available cores for maximum parallelism.</p>
+
+<p>I designed the EBM format with HTTP streaming in mind. Since the pages are laid
+out in the EBM file along predictable boundaries, the e-reader can request
+pages by specifying the offset and the chunk size in the HTTP Range header. Any
+web server will process this request without custom logic.</p>
+
+<h2 id="reflections">Reflections</h2>
+
+<p>It’s been six years since the car park and the displays. I began this project
+hoping to learn the low-level workings of e-paper displays. As a bonus, it led
+me to explore some of ESP32’s most fascinating features: sleep modes, multicore
+processing, DMA, and RTC memory. Embedded systems are magical things: invisible
+particles swirl into form as the programmer whispers C.</p>
 
 <p>Files: <a href="source.tar.gz">source.tar.gz</a></p>
 </div>