Read the payload and trailer byte separately

Reading the payload and the trailer byte separately simplifies the code
in the caller because the destination buffer doesn't need space to store
the extra trailer byte.

Author: jefdriesen

src/cressi_edy.c

@@ -141,9 +141,19 @@ cressi_edy_packet (cressi_edy_device_t *device, const unsigned char command[], u
 			ERROR (abstract->context, "Failed to receive the answer.");
 			return status;
 		}
+	}
+
+	if (trailer) {
+		// Receive the trailer byte.
+		unsigned char end = 0;
+		status = dc_iostream_read (device->iostream, &end, 1, NULL);
+		if (status != DC_STATUS_SUCCESS) {
+			ERROR (abstract->context, "Failed to receive the answer.");
+			return status;
+		}
 
 		// Verify the trailer of the packet.
-		if (trailer && answer[asize - 1] != 0x45) {
+		if (end != 0x45) {
 			ERROR (abstract->context, "Unexpected answer trailer byte.");
 			return DC_STATUS_PROTOCOL;
 		}
@@ -203,9 +213,8 @@ static dc_status_t
 cressi_edy_init3 (cressi_edy_device_t *device)
 {
 	unsigned char command[1] = {0x0C};
-	unsigned char answer[1] = {0};
 
-	return cressi_edy_transfer (device, command, sizeof (command), answer, sizeof (answer), 1);
+	return cressi_edy_transfer (device, command, sizeof (command), NULL, 0, 1);
 }
 
 
@@ -324,6 +333,7 @@ cressi_edy_device_close (dc_device_t *abstract)
 static dc_status_t
 cressi_edy_device_read (dc_device_t *abstract, unsigned int address, unsigned char data[], unsigned int size)
 {
+	dc_status_t status = DC_STATUS_SUCCESS;
 	cressi_edy_device_t *device = (cressi_edy_device_t*) abstract;
 
 	if ((address % SZ_PAGE != 0) ||
@@ -334,22 +344,18 @@ cressi_edy_device_read (dc_device_t *abstract, unsigned int address, unsigned ch
 	while (nbytes < size) {
 		// Read the package.
 		unsigned int number = address / SZ_PAGE;
-		unsigned char answer[SZ_PACKET + 1] = {0};
 		unsigned char command[3] = {0x52,
 				(number >> 8) & 0xFF, // high
 				(number     ) & 0xFF}; // low
-		dc_status_t rc = cressi_edy_transfer (device, command, sizeof (command), answer, sizeof (answer), 1);
-		if (rc != DC_STATUS_SUCCESS)
-			return rc;
-
-		memcpy (data, answer, SZ_PACKET);
+		status = cressi_edy_transfer (device, command, sizeof (command), data + nbytes, SZ_PACKET, 1);
+		if (status != DC_STATUS_SUCCESS)
+			return status;
 
 		nbytes += SZ_PACKET;
 		address += SZ_PACKET;
-		data += SZ_PACKET;
 	}
 
-	return DC_STATUS_SUCCESS;
+	return status;
 }