Fix buffer underflow

marcelstoer · marcelstoer · commit 08885fc9bcc9 · 2026-03-30T18:25:03.000+02:00
Fixes #428
diff --git a/src/SSD1306I2C.h b/src/SSD1306I2C.h
@@ -130,8 +130,10 @@ class SSD1306I2C : public OLEDDisplay {
     }
 
 private:
+	// Reserve 1 byte before the framebuffer so display() can safely write the
+	// I2C control byte (0x40) to buffer[-1] without accessing unallocated memory.
 	int getBufferOffset(void) {
-		return 0;
+		return 1;
 	}
 
     inline void sendCommand(uint8_t command) __attribute__((always_inline)) {

Original file line number	Diff line number	Diff line change
`@@ -130,8 +130,10 @@ class SSD1306I2C : public OLEDDisplay {`
`130`	`130`	`}`
`131`	`131`
`132`	`132`	`private:`
	`133`	`+ // Reserve 1 byte before the framebuffer so display() can safely write the`
	`134`	`+ // I2C control byte (0x40) to buffer[-1] without accessing unallocated memory.`
`133`	`135`	`int getBufferOffset(void) {`
`134`		`- return 0;`
	`136`	`+ return 1;`
`135`	`137`	`}`
`136`	`138`
`137`	`139`	`inline void sendCommand(uint8_t command) __attribute__((always_inline)) {`