From 718093aea3a5a6c80f7fceb1bbbc940168b8d98c Mon Sep 17 00:00:00 2001
From: Bryan Biedenkapp <gatekeep@gmail.com>
Date: Wed, 5 Mar 2025 21:39:46 -0500
Subject: [PATCH] handle serial buffer overflow condition (while the modem
 protocol *can* send frames >512 bytes the serial port handler can only handle
 frames up to 512 bytes); better handle transmitting double length (512 byte)
 P25 PDU frames;

---
 SerialPort.cpp | 13 +++++++++++--
 SerialPort.h   |  5 +++--
 p25/P25TX.cpp  | 30 ++++++++++++++++++++++++------
 p25/P25TX.h    |  2 +-
 4 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/SerialPort.cpp b/SerialPort.cpp
index 3e3c0b5..2e5d296 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -78,8 +78,10 @@ void SerialPort::process()
             if (m_dblFrame) {
                 m_buffer[m_ptr] = c;
                 m_len = ((c & 0xFFU) << 8);
+                // DEBUG3("long frame, len msb", m_len, c);
             } else {
                 m_len = m_buffer[m_ptr] = c;
+                // DEBUG2("short frame, len", m_len);
             }
             m_ptr = 2U;
         }
@@ -87,6 +89,9 @@ void SerialPort::process()
             // Handle the frame length
             m_buffer[m_ptr] = c;
             m_len = (m_len + (c & 0xFFU));
+            if (m_len > SERIAL_FB_LEN)
+                m_len = SERIAL_FB_LEN; // don't allow length to be longer then the buffer
+            // DEBUG3("long frame, len lsb", m_len, c);
             m_ptr = 3U;
         }
         else {
@@ -350,8 +355,12 @@ void SerialPort::process()
                 /** Project 25 */
                 case CMD_P25_DATA:
                     if (m_p25Enable) {
-                        if (m_modemState == STATE_IDLE || m_modemState == STATE_P25)
-                            err = p25TX.writeData(m_buffer + 3U, m_len - 3U);
+                        if (m_modemState == STATE_IDLE || m_modemState == STATE_P25) {
+                            if (m_dblFrame)
+                                err = p25TX.writeData(m_buffer + 4U, m_len - 4U);
+                            else
+                                err = p25TX.writeData(m_buffer + 3U, m_len - 3U);
+                        }
                     }
                     if (err == RSN_OK) {
                         if (m_modemState == STATE_IDLE)
diff --git a/SerialPort.h b/SerialPort.h
index f3a6d55..005160a 100644
--- a/SerialPort.h
+++ b/SerialPort.h
@@ -155,6 +155,7 @@ enum CMD_REASON_CODE {
 const uint8_t DVM_SHORT_FRAME_START = 0xFEU;
 const uint8_t DVM_LONG_FRAME_START = 0xFDU;
 
+#define SERIAL_FB_LEN 518U
 #define SERIAL_SPEED 115200
 /** @} */
 
@@ -287,8 +288,8 @@ public:
     void writeDump(const uint8_t* data, uint16_t length);
 
 private:
-    uint8_t m_buffer[518U];
-    uint8_t m_ptr;
+    uint8_t m_buffer[SERIAL_FB_LEN];
+    uint16_t m_ptr;
     uint16_t m_len;
     bool m_dblFrame;
 
diff --git a/p25/P25TX.cpp b/p25/P25TX.cpp
index ad39ded..2ed41ac 100644
--- a/p25/P25TX.cpp
+++ b/p25/P25TX.cpp
@@ -96,7 +96,7 @@ void P25TX::process()
 
 /* Write data to the local buffer. */
 
-uint8_t P25TX::writeData(const uint8_t* data, uint8_t length)
+uint8_t P25TX::writeData(const uint8_t* data, uint16_t length)
 {
     if (length < (P25_TDU_FRAME_LENGTH_BYTES + 1U))
         return RSN_ILLEGAL_LENGTH;
@@ -108,8 +108,16 @@ uint8_t P25TX::writeData(const uint8_t* data, uint8_t length)
         return RSN_RINGBUFF_FULL;
     }
 
-    m_fifo.put(length - 1U);
-    for (uint8_t i = 0U; i < (length - 1U); i++)
+    if (length <= 255U) {
+        m_fifo.put(DVM_SHORT_FRAME_START);
+        m_fifo.put(length - 1U);
+    } else {
+        m_fifo.put(DVM_LONG_FRAME_START);
+        m_fifo.put(((length - 1U) >> 8U) & 0xFFU);
+        m_fifo.put((length - 1U) & 0xFFU);
+    }
+
+    for (uint16_t i = 0U; i < (length - 1U); i++)
         m_fifo.put(data[i + 1U]);
 
     return RSN_OK;
@@ -182,9 +190,19 @@ void P25TX::createData()
             m_poBuffer[m_poLen++] = P25_START_SYNC;
     }
     else {
-        uint8_t length = m_fifo.get();
+        uint8_t frameType = m_fifo.get();
+        uint16_t length = 0U;
+        switch (frameType) {
+        case DVM_SHORT_FRAME_START:
+            length = m_fifo.get();
+            break;
+        case DVM_LONG_FRAME_START:
+            length = ((m_fifo.get() & 0xFFU) << 8) + (m_fifo.get());
+            break;
+        }
+
         DEBUG3("P25TX::createData() dataLength/fifoSpace", length, m_fifo.getSpace());
-        for (uint8_t i = 0U; i < length; i++) {
+        for (uint16_t i = 0U; i < length; i++) {
             m_poBuffer[m_poLen++] = m_fifo.get();
         }
     }
@@ -198,7 +216,7 @@ void P25TX::createCal()
 {
     // 1.2 kHz sine wave generation
     if (m_modemState == STATE_P25_CAL) {
-        for (unsigned int i = 0U; i < P25_LDU_FRAME_LENGTH_BYTES; i++) {
+        for (uint8_t i = 0U; i < P25_LDU_FRAME_LENGTH_BYTES; i++) {
             m_poBuffer[i] = P25_START_SYNC;
         }
 
diff --git a/p25/P25TX.h b/p25/P25TX.h
index 162e54d..9121177 100644
--- a/p25/P25TX.h
+++ b/p25/P25TX.h
@@ -65,7 +65,7 @@ namespace p25
          * @param length Length of buffer.
          * @returns uint8_t Reason code.
          */
-        uint8_t writeData(const uint8_t* data, uint8_t length);
+        uint8_t writeData(const uint8_t* data, uint16_t length);
 
         /**
          * @brief Clears the local buffer.