From 3acad86d346a2a99893e03a0d69e4974b8344d5a Mon Sep 17 00:00:00 2001
From: Gustav Wiberg <52791556+Guswib@users.noreply.github.com>
Date: Sat, 2 Nov 2024 11:21:21 +0100
Subject: [PATCH 1/3] Update SensirionShdlcTxFrame.cpp

---
 src/SensirionShdlcTxFrame.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/SensirionShdlcTxFrame.cpp b/src/SensirionShdlcTxFrame.cpp
index fc8c4c9..dba0c68 100644
--- a/src/SensirionShdlcTxFrame.cpp
+++ b/src/SensirionShdlcTxFrame.cpp
@@ -38,7 +38,8 @@
 
 uint16_t SensirionShdlcTxFrame::begin(uint8_t command, uint8_t address,
                                       uint8_t dataLength) {
-    _buffer[_index++] = 0x7e;
+    _index=0;                          
+    _buffer[_index] = 0x7e;
     uint16_t error = addUInt8(address);
     error |= addUInt8(command);
     error |= addUInt8(dataLength);

From 451d4eb3b7b1727c5d95329166654bcc2340d396 Mon Sep 17 00:00:00 2001
From: Gustav Wiberg <52791556+Guswib@users.noreply.github.com>
Date: Sat, 2 Nov 2024 11:23:01 +0100
Subject: [PATCH 2/3] Update SensirionShdlcTxFrame.cpp

the begin function sets the index to 0.
---
 src/SensirionShdlcTxFrame.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/SensirionShdlcTxFrame.cpp b/src/SensirionShdlcTxFrame.cpp
index dba0c68..c75e8db 100644
--- a/src/SensirionShdlcTxFrame.cpp
+++ b/src/SensirionShdlcTxFrame.cpp
@@ -38,7 +38,7 @@
 
 uint16_t SensirionShdlcTxFrame::begin(uint8_t command, uint8_t address,
                                       uint8_t dataLength) {
-    _index=0;                          
+    _index=0;                   //sets the index to point towards the start of the buffer.       
     _buffer[_index] = 0x7e;
     uint16_t error = addUInt8(address);
     error |= addUInt8(command);

From b74158446b23e3ec05770c5b040fe03e92dfd84a Mon Sep 17 00:00:00 2001
From: Gustav Wiberg <52791556+Guswib@users.noreply.github.com>
Date: Sat, 2 Nov 2024 12:07:16 +0100
Subject: [PATCH 3/3] SensirionShdlcCommunication::receiveFrame

Fixes issues when an error frame is read, and the datalength-values is not 0.
---
 CHANGELOG.rst                       |  2 ++
 src/SensirionShdlcCommunication.cpp | 19 +++++++++++--------
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 3796359..fba55c6 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -8,6 +8,8 @@ and this project adheres to `Semantic Versioning <https://semver.org/spec/v2.0.0
 
 `Unreleased`_
 -------------
+- update to SensirionShdlcTxFrame::begin so the buffer is always filled from position 0.
+. update to SensirionShdlcCommunication::receiveFrame -  if an error frame is recieved, the data part of the frame should not be read even if the length is not 0.
 
 `0.7.1`_ 2024-04-30
 -------------------
diff --git a/src/SensirionShdlcCommunication.cpp b/src/SensirionShdlcCommunication.cpp
index 3484859..62d2299 100644
--- a/src/SensirionShdlcCommunication.cpp
+++ b/src/SensirionShdlcCommunication.cpp
@@ -124,15 +124,18 @@ uint16_t SensirionShdlcCommunication::receiveFrame(SensirionShdlcRxFrame& frame,
         return RxFrameError | BufferSizeError;
     }
 
-    size_t i = 0;
-    while (i < dataLength) {
-        error = unstuffByte(current, serial, startTime, timeoutMicros);
-        if (error) {
-            return error;
+    // An error frame does not have any data eventhough the value of "dataLength" is not zero.
+    // Therefore, only read data from the buffer if the frame state is 0, i.e, the frame is not of an error frame.
+    
+    if(frame._state == 0 ){
+        for(size_t i = 0; i < dataLength; i++){ 
+            error = unstuffByte(current, serial, startTime, timeoutMicros);
+            if (error) {
+                return error;
+            }
+            frame._buffer[i] = current;
+            checksum += current;
         }
-        frame._buffer[i] = current;
-        checksum += current;
-        i++;
     }
 
     uint8_t expectedChecksum = ~checksum;