From d421b7660c948c2e22798a79aa480343027243c0 Mon Sep 17 00:00:00 2001
From: Guo Wenxue <guowenxue@gmail.com>
Date: Thu, 28 Mar 2019 00:09:04 +0800
Subject: [PATCH] Add tlv makefile and comment for source code
---
ch8_tlv/tlv_sample.c | 21 ++++++++++++++-------
ch8_tlv/makefile | 11 +++++++++++
ch8_tlv/crc-itu-t.h | 28 ++++++++++++++++++++++++++--
3 files changed, 51 insertions(+), 9 deletions(-)
diff --git a/ch8_tlv/crc-itu-t.h b/ch8_tlv/crc-itu-t.h
index 748bf6c..e054724 100644
--- a/ch8_tlv/crc-itu-t.h
+++ b/ch8_tlv/crc-itu-t.h
@@ -13,14 +13,38 @@
#ifndef CRC_ITU_T_H
#define CRC_ITU_T_H
-#define IoT_MAGIC_CRC 0x1E50
+#define MAGIC_CRC 0x1E50
extern const unsigned short crc_itu_t_table[256];
+
+/**
+ * crc_itu_t - Compute the CRC-ITU-T for the data buffer
+ *
+ * @crc: previous CRC value, we use $IoT_MAGIC_CRC
+ * @buffer: data pointer
+ * @len: number of bytes in the buffer
+ *
+ * Returns the updated CRC value
+ */
+extern unsigned short crc_itu_t(unsigned short magic_crc, const unsigned char *buffer, unsigned int len);
+
+
+/*
+ * ushort_to_bytes - Convert unsigned short CRC16 value to two bytes
+ * @bytes: two bytes CRC16 value saving buffer, buffer size must more than 2 bytes
+ * @crc: crc_itu_t() compute returnd value( unsigned short CRC16 checksum)
+ */
extern int ushort_to_bytes(unsigned char *bytes, unsigned short val);
+
+
+/*
+ * bytes_to_ushort - Convert two bytes mode CRC value into unsigned short CRC16 value
+ * @bytes: bytes mode CRC value first byte position
+ * @len: bytes mode CRC value length
+ */
extern unsigned short bytes_to_ushort(unsigned char *bytes, int len);
-extern unsigned short crc_itu_t(unsigned short crc, const unsigned char *buffer, unsigned int len);
static inline unsigned short crc_itu_t_byte(unsigned short crc, const unsigned char data)
{
diff --git a/ch8_tlv/makefile b/ch8_tlv/makefile
new file mode 100644
index 0000000..53d7f60
--- /dev/null
+++ b/ch8_tlv/makefile
@@ -0,0 +1,11 @@
+
+BINAME=tlv_sample
+
+all:
+ gcc *.c -o ${BINAME}
+
+clean:
+ rm -f ${BINAME}
+
+run: all
+ ./${BINAME}
diff --git a/ch8_tlv/tlv_sample.c b/ch8_tlv/tlv_sample.c
index 97bf93a..b86184f 100644
--- a/ch8_tlv/tlv_sample.c
+++ b/ch8_tlv/tlv_sample.c
@@ -29,6 +29,7 @@
#define PACK_HEADER 0xFD
+/* Tag definition */
enum
{
TAG_LOGON=1,
@@ -53,6 +54,8 @@
bytes = packtlv_led(buf, sizeof(buf), ON);
+ /* print every byte in the buffer as HEX and corresponding charactor,
+ which is not printable charactor will be instead as '?' */
dump_buf(buf, bytes);
bytes = packtlv_logon(buf, sizeof(buf), "iot@yun");
@@ -68,7 +71,7 @@
unsigned short crc16 = 0;
int pack_len = 0;
int data_len = 0;
- int ofset = 0;
+ int ofset = 0; /* index position for the buf */
if(!buf || !pwd || size<TLV_MIN_SIZE )
{
@@ -84,7 +87,8 @@
buf[ofset] = TAG_LOGON;
ofset += 1;
- /* $pwd too long maybe result buffer overflow, if it's too long then truncate it */
+ /* $pwd too long maybe result buffer overflow, so we need check the buffer
+ * is large enuf or not. If buf size is not enuf we will truncate $pwd string */
if( strlen(pwd) <= size-TLV_FIXED_SIZE )
data_len = strlen(pwd);
else
@@ -99,8 +103,10 @@
memcpy(&buf[ofset], pwd, data_len);
ofset += data_len;
- /* Calc CRC16 value from Packet Head(buf[0])~ Packet Value(buf[ofset]) */
- crc16 = crc_itu_t(IoT_MAGIC_CRC, buf, ofset);
+ /* Calc CRC16 checksum value from Packet Head(buf[0])~ Value(buf[ofset]) */
+ crc16 = crc_itu_t(MAGIC_CRC, buf, ofset);
+
+ /* Append the 2 Bytes CRC16 checksum value into the last two bytes in packet buffer */
ushort_to_bytes(&buf[ofset], crc16);
ofset += 2;
@@ -132,10 +138,10 @@
/* Value */
buf[3] = (OFF==cmd) ? 0x00 : 0x01;
- /* Calc CRC16 value from Packet Head(buf[0])~ Packet Value(buf[3]) */
- crc16 = crc_itu_t(IoT_MAGIC_CRC, buf, 4);
+ /* Calc CRC16 checksum value from Packet Head(buf[0])~ Packet Value(buf[3]) */
+ crc16 = crc_itu_t(MAGIC_CRC, buf, 4);
- /* Append the 2 Bytes CRC16 value into the packet buffer */
+ /* Append the 2 Bytes CRC16 checksum value into the last two bytes in packet buffer */
ushort_to_bytes(&buf[4], crc16);
return pack_len;
@@ -167,6 +173,7 @@
"????????????????"
"????????????????";
+/* print every byte in the buffer as HEX and corresponding charactor, which is not printable charactor will be instead as '?' */
void dump_buf(char *data, int len)
{
int rc;
--
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