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Merge branch 'doc/crc_apis_usage' into 'master' 

Add CRC APIs usage

See merge request idf/esp-idf!4351
pull/3118/head
Jiang Jiang Jian 2019-03-01 10:03:03 +08:00
rodzic 6c49f19247 299e4ca716
commit ebdcbe8c60
1 zmienionych plików z 45 dodań i 12 usunięć
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57
components/esp32/include/rom/crc.h
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@ -30,15 +30,48 @@ extern "C" {
*/
/* Standard CRC8/16/32 algorithms. */
// CRC-8 x8+x2+x1+1 0x07
// CRC16-CCITT x16+x12+x5+1 1021 ISO HDLC, ITU X.25, V.34/V.41/V.42, PPP-FCS
// CRC32:
//G(x) = x32 +x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x1 + 1
//If your buf is not continuous, you can use the first result to be the second parameter.
/* Notes about CRC APIs usage
* The ESP32 ROM include some CRC tables and CRC APIs to speed up CRC calculation.
* The CRC APIs include CRC8, CRC16, CRC32 algorithms for both little endian and big endian modes.
* Here are the polynomials for the algorithms:
* CRC-8 x8+x2+x1+1 0x07
* CRC16-CCITT x16+x12+x5+1 0x1021
* CRC32 x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x1+1 0x04c11db7
*
* These group of CRC APIs are designed to calculate the data in buffers either continuous or not.
* To make it easy, we had added a `~` at the beginning and the end of the functions.
* To calculate non-continuous buffers, we can write the code like this:
* init = ~init;
* crc = crc32_le(init, buf0, length0);
* crc = crc32_le(crc, buf1, length1);
* crc = ~crc;
*
* However, it is not easy to select which API to use and give the correct parameters.
* A specific CRC algorithm will include this parameters: width, polynomials, init, refin, refout, xorout
* refin and refout show the endian of the algorithm:
* if both of them are true, please use the little endian API.
* if both of them are false, please use the big endian API.
* xorout is the value which you need to be xored to the raw result.
* However, these group of APIs need one '~' before and after the APIs.
*
* Here are some examples for CRC16:
* CRC-16/CCITT, poly = 0x1021, init = 0x0000, refin = true, refout = true, xorout = 0x0000
* crc = ~crc16_le((uint16_t)~0x0000, buf, length);
*
* CRC-16/CCITT-FALSE, poly = 0x1021, init = 0xffff, refin = false, refout = false, xorout = 0x0000
* crc = ~crc16_be((uint16_t)~0xffff, buf, length);
*
* CRC-16/X25, poly = 0x1021, init = 0xffff, refin = true, refout = true, xorout = 0xffff
* crc = (~crc16_le((uint16_t)~(0xffff), buf, length))^0xffff;
*
* CRC-16/XMODEM, poly= 0x1021, init = 0x0000, refin = false, refout = false, xorout = 0x0000
* crc = ~crc16_be((uint16_t)~0x0000, buf, length);
*
*
*/
/**
* @brief Crc32 value that is in little endian.
* @brief CRC32 value that is in little endian.
*
* @param uint32_t crc : init crc value, use 0 at the first use.
*
@ -51,7 +84,7 @@ extern "C" {
uint32_t crc32_le(uint32_t crc, uint8_t const *buf, uint32_t len);
/**
* @brief Crc32 value that is in big endian.
* @brief CRC32 value that is in big endian.
*
* @param uint32_t crc : init crc value, use 0 at the first use.
*
@ -64,7 +97,7 @@ uint32_t crc32_le(uint32_t crc, uint8_t const *buf, uint32_t len);
uint32_t crc32_be(uint32_t crc, uint8_t const *buf, uint32_t len);
/**
* @brief Crc16 value that is in little endian.
* @brief CRC16 value that is in little endian.
*
* @param uint16_t crc : init crc value, use 0 at the first use.
*
@ -77,7 +110,7 @@ uint32_t crc32_be(uint32_t crc, uint8_t const *buf, uint32_t len);
uint16_t crc16_le(uint16_t crc, uint8_t const *buf, uint32_t len);
/**
* @brief Crc16 value that is in big endian.
* @brief CRC16 value that is in big endian.
*
* @param uint16_t crc : init crc value, use 0 at the first use.
*
@ -90,7 +123,7 @@ uint16_t crc16_le(uint16_t crc, uint8_t const *buf, uint32_t len);
uint16_t crc16_be(uint16_t crc, uint8_t const *buf, uint32_t len);
/**
* @brief Crc8 value that is in little endian.
* @brief CRC8 value that is in little endian.
*
* @param uint8_t crc : init crc value, use 0 at the first use.
*
@ -103,7 +136,7 @@ uint16_t crc16_be(uint16_t crc, uint8_t const *buf, uint32_t len);
uint8_t crc8_le(uint8_t crc, uint8_t const *buf, uint32_t len);
/**
* @brief Crc8 value that is in big endian.
* @brief CRC8 value that is in big endian.
*
* @param uint32_t crc : init crc value, use 0 at the first use.
*