Neo4J post update.

2 files changed, 30 insertions, 25 deletions

diff --git a/_log/e-reader.md b/_log/e-reader.md
index 2edd5dd..fbc7b94 100644
--- a/_log/e-reader.md
+++ b/_log/e-reader.md
@@ -12,25 +12,26 @@ First project with e-paper displays and ESP32.
   <source src="ereader.mp4" type="video/mp4">
 </video>
 
-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)
@@ -59,11 +60,14 @@ void epd_draw_async(const uint8_t *buf, size_t n)
 }
 ```
 
-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](../etlas/).
+Verdict: Works but limited. Led to [Etlas](../etlas/).
 
 Commit:
 [7f691c4](https://git.asciimx.com/esp32-e-reader/commit/?id=7f691c46093933b67aab466c0ca582ace8ab73d4)
diff --git a/_log/neo4j-a-star-search.md b/_log/neo4j-a-star-search.md
index 3233428..fe6f33f 100644
--- a/_log/neo4j-a-star-search.md
+++ b/_log/neo4j-a-star-search.md
@@ -4,13 +4,11 @@ date: 2018-03-06
 layout: post
 ---
 
-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(
@@ -50,7 +48,10 @@ private void updateCosts(
 }
 ```
 
-Outcome: 300x speedup. Scaled to 13,000 route points. Upstreamed changes. <a
+Outcome: 300x speedup. Scaled to 13,000 route points. 
+
+Upstreamed changes: <a
 href="https://github.com/neo4j-contrib/neo4j-graph-algorithms/releases/tag/3.4.0.0"
-class="external" target="_blank" rel="noopener noreferrer">Neo4J v3.4.0</a>.
-[Full source](https://github.com/neo4j-contrib/neo4j-graph-algorithms/blob/bd9732d9a690319552e134708692acb5a0d6b37c/algo/src/main/java/org/neo4j/graphalgo/impl/ShortestPathAStar.java)
+class="external" target="_blank" rel="noopener noreferrer">Neo4J v3.4.0</a> | 
+[Full
+source](https://github.com/neo4j-contrib/neo4j-graph-algorithms/blob/bd9732d9a690319552e134708692acb5a0d6b37c/algo/src/main/java/org/neo4j/graphalgo/impl/ShortestPathAStar.java)