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Diffstat (limited to '_log')
| -rw-r--r-- | _log/e-reader.md | 38 |
1 files changed, 18 insertions, 20 deletions
diff --git a/_log/e-reader.md b/_log/e-reader.md index a1f1b0a..a754a52 100644 --- a/_log/e-reader.md +++ b/_log/e-reader.md @@ -1,29 +1,26 @@ --- -title: 512 KB e-reader +title: Built a 0 MB streaming e-reader date: 2023-10-24 layout: post project: true thumbnail: thumb_sm.png --- -Been dabbling in microcontrollers—mostly Arduino Uno/ATmega328P. Math major, no -formal electronics training. This, however, is an ESP-32 project—first -resembling something practical. +Built an e-reader using an ESP-WROOM-32, a 7.5" Waveshare e-paper display, and +a three-button interface (prev/next/sleep). <video style="max-width:100%;" controls="" poster="poster.png"> <source src="ereader.mp4" type="video/mp4"> </video> -ESP-WROOM-32, 7.5" Waveshare e-paper display, three-button interface -(prev/next/sleep). +ESP-32-WROOM has 512 KB SRAM and 4 MB flash. Internal flash is unsuitable for +storing books due to P/E cycle limit. Used HTTP Range requests to stream them +on-demand. Saved reading progress to RTC memory to survive deep sleep without +flash wear. -Memory: 512 KB SRAM + 4 MB flash. Internal flash unsuitable for storing books -due to P/E cycle limit. Used HTTP Range requests to stream them on-demand. -Progress saved to RTC memory to survive deep sleep without flash wear. - -PDFs are rasterized and stored as sequences of bitmaps on a server. 1 byte = 8 -pixels, 1 page = 48 KB (display resolution), headerless. Optimized for Range -requests without server-side logic: +Rasterized PDFs into sequences of bitmaps. 1 byte = 8 pixels, 1 page = 48 KB +(display resolution), headerless. Optimized for Range requests without +server-side logic: ``` int r0 = ((page_n - 1) * PAGE_SIZE); @@ -37,9 +34,9 @@ esp_http_client_set_header(http_client, "Range", buf); esp_http_client_perform(http_client); ``` -Three pages (prev/current/next) stored in a circular buffer—max possible. Upon -request (via GPIO interrupts), application cycles buffer, updates screen, -prefetches next page. +Implemented a three-page circular buffer (prev/current/next)—maximum possible +with 512 KB. GPIO interrupts triggered by button presses cycle the buffer, +update the screen, and prefetch the next page. ``` c_page_num++; @@ -54,12 +51,13 @@ epd_draw_await(); ``` System isn't as responsive as I'd hoped. Scheduling GPIO, SPI, and HTTP tasks -on a single thread causes input lag. Pinned GPIO/SPI tasks to one core and the -HTTP task to the other. +on a single core causes input lag. Pinned the GPIO/SPI tasks to one core and +the HTTP task to the other. -Better, but screen updates block user input. +Better, but screen updates block user input; page turning feels sluggish. -Moved SPI buffers to DMA and made transfers async. Few more cycles saved. +Moved the SPI buffers to DMA and made the transfers async, hoping to shave off +a few more cycles. Can't think of anything else. Led to [Etlas](../etlas/). |