Implementation of xmodem data reception

openrtx/include/core/xmodem.h

@@ -37,6 +37,15 @@ extern "C" {
  */
 void xmodem_sendPacket(const void *data, size_t size, uint8_t blockNum);
 
+/**
+ * Receive an XMODEM packet from the serial port.
+ *
+ * @param data: pointer to a buffer for payload data.
+ * @param expectedBlockNum: expected block number, for sanity check.
+ * @return number of bytes received or zero in case of errors.
+ */
+size_t xmodem_receivePacket(void *data, uint8_t expectedBlockNum);
+
 /**
  * Send data using the XMODEM protocol, blocking function.
  * Data transfer begins when the start command from the receiving endpoint is
@@ -45,9 +54,20 @@ void xmodem_sendPacket(const void *data, size_t size, uint8_t blockNum);
  * @param size: data size.
  * @param callback: pointer to a callback function in charge of providing data
  * for the new packets being sent.
+ * @return number of bytes sent.
  */
 ssize_t xmodem_sendData(size_t size, int (*callback)(uint8_t *, size_t));
 
+/**
+ * Receive data using the XMODEM protocol, blocking function.
+ * Transfer starts immediately when this function is called.
+ *
+ * @param size: expected data size, in bytes.
+ * @param callback: callback function invoked when a new data block is recevied.
+ * @return number of bytes received.
+ */
+ssize_t xmodem_receiveData(size_t size, void (*callback)(uint8_t *, size_t));
+
 #ifdef __cplusplus
 }
 #endif

openrtx/src/core/xmodem.c

@@ -25,16 +25,15 @@
 #include <string.h>
 #include <crc.h>
 
-#define SOH     (0x01)  /* start of 128-byte data packet */
-#define STX     (0x02)  /* start of 1024-byte data packet */
-#define EOT     (0x04)  /* End Of Transmission */
-#define ACK     (0x06)  /* ACKnowledge, receive OK */
-#define NAK     (0x15)  /* Negative ACKnowledge, receiver ERROR, retry */
-#define CAN     (0x18)  /* two CAN in succession will abort transfer */
-#define CRC     (0x43)  /* 'C' == 0x43, request 16-bit CRC, use in place of first NAK for CRC mode */
-#define ABT1    (0x41)  /* 'A' == 0x41, assume try abort by user typing */
-#define ABT2    (0x61)  /* 'a' == 0x61, assume try abort by user typing */
-
+#define SOH     (0x01)  // start of 128-byte data packet
+#define STX     (0x02)  // start of 1024-byte data packet
+#define EOT     (0x04)  // End Of Transmission
+#define ACK     (0x06)  // ACKnowledge, receive OK
+#define NAK     (0x15)  // Negative ACKnowledge, receiver ERROR, retry
+#define CAN     (0x18)  // two CAN in succession will abort transfer
+#define CRC     (0x43)  // 'C' == 0x43, request 16-bit CRC, use in place of first NAK for CRC mode
+#define ABT1    (0x41)  // 'A' == 0x41, assume try abort by user typing
+#define ABT2    (0x61)  // 'a' == 0x61, assume try abort by user typing
 
 /**
  * @internal
@@ -86,6 +85,39 @@ void xmodem_sendPacket(const void *data, size_t size, uint8_t blockNum)
     vcom_writeBlock(buf, 2);
 }
 
+size_t xmodem_receivePacket(void* data, uint8_t expectedBlockNum)
+{
+    // Get first byte
+    uint8_t status = 0;
+    while((status != STX) && (status != SOH))
+    {
+        waitForData(&status, 1);
+    }
+
+    // Get sequence number
+    uint8_t seq[2] = {0};
+    waitForData(seq, 2);
+
+    // Determine payload size and get data
+    size_t blockSize = 128;
+    if(status == STX) blockSize = 1024;
+    waitForData(((uint8_t *) data), blockSize);
+
+    // Get CRC
+    uint8_t crc[2] = {0};
+    waitForData(crc, 2);
+
+    // First sanity check: sequence number
+    if((seq[0] ^ seq[1]) != 0xFF)  return 0;
+    if(expectedBlockNum != seq[0]) return 0;
+
+    // Second sanity check: CRC
+    uint16_t dataCrc = crc_ccitt(data, blockSize);
+    if((crc[0] != (dataCrc >> 8)) || (crc[1] != (dataCrc & 0xFF))) return 0;
+
+    return blockSize;
+}
+
 ssize_t xmodem_sendData(size_t size, ssize_t (*callback)(uint8_t *, size_t))
 {
     // Wait for the start command from the receiver, only CRC mode is supported.
@@ -158,3 +190,52 @@ ssize_t xmodem_sendData(size_t size, ssize_t (*callback)(uint8_t *, size_t))
 
     return sentSize;
 }
+
+ssize_t xmodem_receiveData(size_t size, void (*callback)(uint8_t *, size_t))
+{
+    uint8_t dataBuf[1024];
+    uint8_t command  = 0;
+    uint8_t blockNum = 1;
+    size_t  rcvdSize = 0;
+
+    // Request data transfer in CRC mode
+    command = CRC;
+    vcom_writeBlock(&command, 1);
+
+    while(rcvdSize < size)
+    {
+        size_t blockSize = xmodem_receivePacket(dataBuf, blockNum);
+        if(blockSize == 0)
+        {
+            // Bad packet, send NACK
+            command = NAK;
+        }
+        else
+        {
+            // New data arrived
+            size_t delta = size - rcvdSize;
+            if(blockSize < delta) delta = blockSize;
+            callback(dataBuf, delta);
+
+            rcvdSize += delta;
+            blockNum++;
+
+            // ACK and go on
+            command = ACK;
+        }
+
+        vcom_writeBlock(&command, 1);
+    }
+
+    // Wait for EOT from the sender, ACK and return
+    uint8_t status = 0;
+    while(status != EOT)
+    {
+        waitForData(&status, 1);
+    }
+
+    command = ACK;
+    vcom_writeBlock(&command, 1);
+
+    return rcvdSize;
+}