From f58e85e10e6a16031f0e8f4293c5267dd4614d7b Mon Sep 17 00:00:00 2001
From: shtirlic <serg@podtynnyi.com>
Date: Sat, 19 Apr 2025 14:17:17 +0700
Subject: [PATCH] Fix i2c slave scl freeze if read address first recieved

If i2c master performs discovery via address read, stm32 has no data to
send for the masterin requestEvent. Send the zero byte if we got
requestEvent early, for example on i2c address read.
---
 Code/picocalc_keyboard/picocalc_keyboard.ino | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/Code/picocalc_keyboard/picocalc_keyboard.ino b/Code/picocalc_keyboard/picocalc_keyboard.ino
index 33fe4e4..65db179 100644
--- a/Code/picocalc_keyboard/picocalc_keyboard.ino
+++ b/Code/picocalc_keyboard/picocalc_keyboard.ino
@@ -36,7 +36,7 @@ void set_pmu_flag(void) { pmu_flag = true; }
 
 HardwareSerial Serial1(PA10, PA9);
 
-uint8_t write_buffer[10];
+uint8_t write_buffer[10] = {0};
 uint8_t write_buffer_len = 0;
 
 uint8_t io_matrix[9];//for IO matrix,last bytye is the restore key(c64 only)
@@ -180,7 +180,13 @@ void receiveEvent(int howMany) {
 }
 
 //-this is after receiveEvent-------------------------------
-void requestEvent() { Wire.write(write_buffer,write_buffer_len ); }
+void requestEvent() {
+  if (write_buffer_len > 0 && write_buffer_len <= sizeof(write_buffer)) {
+    Wire.write(write_buffer,write_buffer_len );
+  } else {
+    Wire.write((uint8_t)0); // Send something minimal to avoid stalling
+  }
+}
 
 void report_bat(){
  if (PMU.isBatteryConnect()) {