Sensible max size.

Author: microbit-matt-hillsdon

src/board/data-logging.ts

@@ -11,8 +11,10 @@ import {
 } from "./constants";
 import { State } from "./state";
 
-// TODO: Check this value
-const maxSize = 124 * 1024;
+// Determined via a CODAL program dumping logEnd - dataStart in MicroBitLog.cpp.
+// This is only approximate as we don't serialize our state in the same way but
+// it's important for the user to see that the log can fill up.
+const maxSizeBytes = 118780;
 
 export class DataLogging {
   private mirroring: boolean = false;
@@ -93,7 +95,7 @@ export class DataLogging {
 
     if (entry.data || entry.headings) {
       const entrySize = calculateEntrySize(entry);
-      if (this.size + entrySize > maxSize) {
+      if (this.size + entrySize > maxSizeBytes) {
         if (!this.logFull) {
           this.logFull = true;
           this.onChange({
@@ -163,11 +165,12 @@ function noRowError() {
 }
 
 function calculateEntrySize(entry: LogEntry): number {
+  // +1s for commas and a newline, approximating the CSV in the flash.
   const headings = entry.headings
-    ? entry.headings.reduce((prev, curr) => prev + curr.length, 0)
+    ? entry.headings.reduce((prev, curr) => prev + curr.length + 1, 0) + 1
     : 0;
   const data = entry.data
-    ? entry.data.reduce((prev, curr) => prev + curr.length, 0)
+    ? entry.data.reduce((prev, curr) => prev + curr.length + 1, 0) + 1
     : 0;
   return headings + data;
 }