From 75aa500d7644f15f4a45fe2f64de1c526b87cf95 Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Sun, 4 Jan 2026 18:17:43 +0800 Subject: Neo4J post update. --- _site/log/e-reader/index.html | 36 ++++++++++++++++++-------------- _site/log/neo4j-a-star-search/index.html | 17 ++++++++------- 2 files changed, 29 insertions(+), 24 deletions(-) (limited to '_site/log') diff --git a/_site/log/e-reader/index.html b/_site/log/e-reader/index.html index 23d409b..a5dbc01 100644 --- a/_site/log/e-reader/index.html +++ b/_site/log/e-reader/index.html @@ -46,25 +46,26 @@ -

ESP-WROOM-32, 7.5” Waveshare e-paper display, three buttons (prev/next/sleep).

+

System: ESP-WROOM-32, 7.5” Waveshare e-paper display, three buttons +(prev/next/sleep).

-

No local storage—streams books over HTTP. RTC memory tracks reading progress -between sessions.

+

2023-09-23: 512KB SRAM, 4MB flash (shared with FreeRTOS and ESP-IDF). Not +enough storage for books. Using ESP32’s built-in WiFi to stream them over HTTP. +Recording the reading progress in RTC memory.

-

ESP32: 512KB SRAM, 4MB flash (shared with FreeRTOS, ESP-IDF). Not enough to -store books. Stream from webserver instead.

+

Rasterized pages encoded as tightly packed bitmaps (1 byte => 8 pixels), no +headers, arranged along 48 KB (480x800) boundaries; Reader can stream pages +using HTTP Range requests with zero server-side logic. Keeps both ends lean.

-

Custom EBM file format. Rasterized monochrome bitmaps, one per page (480x800). -One byte = 8 pixels. Pages on 48KB boundaries—HTTP Range requests work without -server logic. pdftoebm.py converts PDFs.

+

Page table stores 3 pages (prev/current/next) in a circular buffer. When the +user requests a page, program cycles through the table, updates the screen, and +downloads the next page.

-

Circular buffer holds 3 pages (prev/current/next)–page table. Single-threaded -approach too slow—user input, SPI, and HTTP on one core causes lag.

+

Responsiveness is inadequate. Scheduling GPIO (user input), SPI, and HTTP on +one core causes input lag. Pinned the GPIO and SPI tasks to one core, the HTTP +task to the other core.

-

Optimizations: pin the GPIO task (responding to user input and updating -display) to one core, pin the HTTP task to the other core.

- -

Better, but system unresponsive during screen updates. Made SPI transfer async:

+

Better, but screen updates are blocking user input; Made SPI transfer async:

void epd_draw_async(const uint8_t *buf, size_t n)
 {
@@ -92,11 +93,14 @@ display) to one core, pin the HTTP task to the other core.

 }
-

Much better. Squeeze a few more cycles by moving SPI buffer to DMA.

+

Much better.

+ +

2023-10-06: Moved the page table to DMA-capable memory; Reclaimed a few more +CPU cycles from the SPI transfers.

Can’t think of anything else.

-

Outcome: Works but limited. Led to Etlas.

+

Verdict: Works but limited. Led to Etlas.

Commit: 7f691c4

diff --git a/_site/log/neo4j-a-star-search/index.html b/_site/log/neo4j-a-star-search/index.html index 00f7886..c8c4ce6 100644 --- a/_site/log/neo4j-a-star-search/index.html +++ b/_site/log/neo4j-a-star-search/index.html @@ -40,13 +40,11 @@

NEO4J SHORTEST PATH OPTIMIZATION

06 MARCH 2018

-

Replaced Dijkstra’s search for vessel route tracking in Neo4J.

+

Work project. Marine vessel tracking with Neo4J hit a limit. Need to store +13,000 route points; Dijkstra’s shortest path search slows after 4,000.

-

Tracking 13,000 marine vessel route points. Needed shortest paths between ports -for arrival prediction. Neo4j’s Dijkstra’s algorithm slows after 4,000 route -points.

- -

Implemented A* search using haversine function as heuristic:

+

Replaced Dijkstra’s algorithm with A* search using haversine function as +heuristic:

private double computeHeuristic(
     final double lat1, final double lon1,
@@ -84,8 +82,11 @@ points.

 }
-

Outcome: 300x speedup. Scaled to 13,000 route points. Upstreamed changes. Neo4J v3.4.0. -Full source

+

Outcome: 300x speedup. Scaled to 13,000 route points.

+ +

Upstreamed changes: Neo4J v3.4.0 | +Full +source

by W. D. Sadeep Madurange

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