Support up to 65kB of payload using 16-bit frame length

Author: bojanpotocnik

target/min.c

@@ -23,7 +23,8 @@ enum {
     SEARCHING_FOR_SOF,
     RECEIVING_ID_CONTROL,
     RECEIVING_SEQ,
-    RECEIVING_LENGTH,
+    RECEIVING_LENGTH_MSB,
+    RECEIVING_LENGTH_LSB,
     RECEIVING_PAYLOAD,
     RECEIVING_CHECKSUM_3,
     RECEIVING_CHECKSUM_2,
@@ -493,15 +494,26 @@ static void rx_byte(struct min_context *self, uint8_t byte)
             }
             else {
                 self->rx_frame_seq = 0;
-                self->rx_frame_state = RECEIVING_LENGTH;
+                self->rx_frame_state = RECEIVING_LENGTH_MSB;
             }
             break;
         case RECEIVING_SEQ:
             self->rx_frame_seq = byte;
             crc32_step(&self->rx_checksum, byte);
-            self->rx_frame_state = RECEIVING_LENGTH;
+            self->rx_frame_state = RECEIVING_LENGTH_MSB;
             break;
-        case RECEIVING_LENGTH:
+        case RECEIVING_LENGTH_MSB:
+#if (MAX_PAYLOAD > UINT8_MAX)
+            self->rx_frame_length = ((uint16_t)byte) << 8;
+            crc32_step(&self->rx_checksum, byte);
+            self->rx_frame_state = RECEIVING_LENGTH_LSB;
+            break;
+#else
+            // MSB == LSB if value is 8-bit
+            self->rx_frame_state = RECEIVING_LENGTH_LSB;
+#endif
+            // FALLTHRU
+        case RECEIVING_LENGTH_LSB:
             self->rx_frame_length = byte;
             self->rx_control = byte;
             crc32_step(&self->rx_checksum, byte);

target/min.h

@@ -86,8 +86,8 @@
 #define TRANSPORT_FIFO_MAX_FRAMES                   (1U << TRANSPORT_FIFO_SIZE_FRAMES_BITS)
 #define TRANSPORT_FIFO_MAX_FRAME_DATA               (1U << TRANSPORT_FIFO_SIZE_FRAME_DATA_BITS)
 
-#if (MAX_PAYLOAD > 255)
-#error "MIN frame payloads can be no bigger than 255 bytes"
+#if (MAX_PAYLOAD > 0xFFFF)
+#error "MIN frame payloads can be no bigger than 65535 (0xFFFF) bytes"
 #endif
 
 // Indices into the frames FIFO are uint8_t and so can't have more than 256 frames in a FIFO
@@ -149,7 +149,11 @@ struct min_context {
     uint8_t rx_frame_payload_bytes;                 // Length of payload received so far
     uint8_t rx_frame_id_control;                    // ID and control bit of frame being received
     uint8_t rx_frame_seq;                           // Sequence number of frame being received
+#if (MAX_PAYLOAD > UINT8_MAX)
+    uint16_t rx_frame_length;                       // Length of frame
+#else
     uint8_t rx_frame_length;                        // Length of frame
+#endif
     uint8_t rx_control;                             // Control byte
     uint8_t tx_header_byte_countdown;               // Count out the header bytes
     uint8_t port;                                   // Number of the port associated with the context