Workaround for Holley DTZ541 (#76)

* Fix Issues - handling incorrect sml_time object - support crc-16/kermit algorithm * fix review findings * fixed review findings * revert indentation change
volkszaehler · Oct 31, 2019 · 36fc784 · 36fc784
1 parent bbe2127
commit 36fc784
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Showing 4 changed files with 40 additions and 14 deletions.
diff --git a/sml/include/sml/sml_crc16.h b/sml/include/sml/sml_crc16.h
@@ -28,6 +28,9 @@ extern "C" {
 // CRC16 FSC implementation based on DIN 62056-46
 u16 sml_crc16_calculate(unsigned char *cp, int len) ;
 
+// CRC-16/CCITT(Kermit) implementation poly=0x1021 init=0x0000 refin=true refout=true xorout=0x0000
+u16 sml_crc16kermit_calculate(unsigned char *cp, int len) ;
+
 #ifdef __cplusplus
 }
 #endif

diff --git a/sml/src/sml_crc16.c b/sml/src/sml_crc16.c
@@ -22,7 +22,7 @@
 #define PPPINITFCS16 0xffff	// initial FCS value
 
 // table taken from DIN EN 62056-46
-static u16 fcstab [256] = { 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48,
+static u16 crctab [256] = { 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48,
 		0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c,
 		0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210,
 		0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
@@ -48,7 +48,7 @@ u16 sml_crc16_calculate(unsigned char *cp, int len) {
 	u16 fcs = PPPINITFCS16;
 
 	while (len--) {
-		fcs = (fcs >> 8) ^ fcstab[(fcs ^ *cp++) & 0xff];
+		fcs = (fcs >> 8) ^ crctab[(fcs ^ *cp++) & 0xff];
 	}
 
 	fcs ^= 0xffff;
@@ -57,3 +57,12 @@ u16 sml_crc16_calculate(unsigned char *cp, int len) {
 	return fcs;
 }
 
+u16 sml_crc16kermit_calculate(unsigned char *cp, int len) {
+    u16 crc = 0x000;
+
+    while (len--) {
+        crc = (crc >> 8) ^ crctab[(crc ^ *cp++) & 0xff];
+    }
+
+    return crc;
+}
diff --git a/sml/src/sml_message.c b/sml/src/sml_message.c
@@ -68,8 +68,11 @@ sml_message *sml_message_parse(sml_buffer *buf) {
 
 	msg->crc = sml_u16_parse(buf);
 	if (sml_buf_has_errors(buf)) goto error;
-	if (*msg->crc != sml_crc16_calculate(&(buf->buffer[msg_start]), len))
-		goto error;
+
+    if (*msg->crc != sml_crc16_calculate(&(buf->buffer[msg_start]), len))
+        // Workaround for Holley DTZ541 uses CRC-16/Kermit
+        if(*msg->crc != sml_crc16kermit_calculate(&(buf->buffer[msg_start]), len))
+		    goto error;
 
 	if (sml_buf_get_current_byte(buf) == SML_MESSAGE_END) {
 		sml_buf_update_bytes_read(buf, 1);

diff --git a/sml/src/sml_time.c b/sml/src/sml_time.c
@@ -38,18 +38,29 @@ sml_time *sml_time_parse(sml_buffer *buf) {
 
 	sml_time *tme = sml_time_init();
 
-	if (sml_buf_get_next_type(buf) != SML_TYPE_LIST) {
-		buf->error = 1;
-		goto error;
-	}
+    // workaround Holley DTZ541
+    // if SML_ListEntry valTime (SML_Time) is given there are missing bytes:
+    // 0x72: indicate a list for SML_Time with 2 entries
+    // 0x62 0x01: indicate secIndex
+    // instead, the DTZ541 starts with 0x65 + 4 bytes secIndex
+    // the workaround will add this information during parsing
+    if (sml_buf_get_current_byte(buf) == (SML_TYPE_UNSIGNED | 5)) {
+        tme->tag = malloc(sizeof(u8));
+        *(tme->tag) = SML_TIME_SEC_INDEX;
+    } else {
+        if (sml_buf_get_next_type(buf) != SML_TYPE_LIST) {
+            buf->error = 1;
+            goto error;
+        }
 
-	if (sml_buf_get_next_length(buf) != 2) {
-		buf->error = 1;
-		goto error;
-	}
+		if (sml_buf_get_next_length(buf) != 2) {
+			buf->error = 1;
+			goto error;
+		}
 
-	tme->tag = sml_u8_parse(buf);
-	if (sml_buf_has_errors(buf)) goto error;
+		tme->tag = sml_u8_parse(buf);
+		if (sml_buf_has_errors(buf)) goto error;
+    }
 
 	int type = sml_buf_get_next_type(buf);
 	switch (type) {