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diff --git a/_projects/e-reader.md b/_projects/e-reader.md index 1a0892e..dcafca0 100644 --- a/_projects/e-reader.md +++ b/_projects/e-reader.md @@ -1,14 +1,14 @@ --- -title: Prototype e-reader +title: Experimental e-reader date: 2023-10-24 thumbnail: thumb.png layout: post --- -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. +This project features a minimal 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 built +with the intention of learning about e-paper displays. <video style="max-width:100%;" controls="" poster="thumb.png"> <source src="ereader.mp4" type="video/mp4"> @@ -57,20 +57,20 @@ PDF documents to EBM files. ## How does it work? -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 `EBM_ARCH_URL` -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 `EBM_ARCH_URL` value, -which requires recompiling the embedded software. +As the e-reader has no storage, it can't store books locally. Instead, it +downloads pages of the EBM file over HTTP from the location pointed to by the +`EBM_ARCH_URL` setting in the Kconfig.projbuild file on demand. To read a +different book, we have to replace the old file with the new one or change the +`EBM_ARCH_URL` value. The latter requires us to recompile the embedded +software. 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 -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. +circular buffer in DMA-capable memory. When the user turns a page by pressing a +button, one of the 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 used the ESP-IDF's task API to distribute the two +tasks between the available cores to make the reader more responsive. 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 @@ -80,11 +80,15 @@ web server will process this request without custom logic. ## Reflections 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. - - +hoping to learn more about e-paper displays, and I got that and more. By +working within the constraints of the ESP32, I forced myself to explore some of +its advanced features: sleep modes, multicore task scheduling, DMA transfers, +and RTC memory. + +As for the prototype, while it's no match for a commercial e-reader with +features like an offline library of books and touch screens, there's something +to be said about reading on hardware you built yourself. You are no longer the +powerless Muggle watching others perform magic. You are the wizard who makes +the invisible particles swirl into form by whispering C to it. Files: [source.tar.gz](source.tar.gz) |