mirror of
https://github.com/RobTillaart/Arduino.git
synced 2024-10-03 18:09:02 -04:00
137 lines
5.1 KiB
Markdown
137 lines
5.1 KiB
Markdown
|
|
[](https://github.com/marketplace/actions/arduino_ci)
|
|
[](https://github.com/RobTillaart/CRC/actions/workflows/arduino-lint.yml)
|
|
[](https://github.com/RobTillaart/CRC/actions/workflows/jsoncheck.yml)
|
|
[](https://github.com/RobTillaart/CRC/blob/master/LICENSE)
|
|
[](https://github.com/RobTillaart/CRC/releases)
|
|
|
|
|
|
# CRC
|
|
|
|
Arduino library with CRC8, CRC16, CRC32 and CRC64 functions.
|
|
|
|
|
|
## Description
|
|
|
|
Goal of this library is to have a flexible and portable set of generic
|
|
CRC functions and classes.
|
|
|
|
The CRCx classes have a number of added values. Most important is that
|
|
they allow one to verify intermediate CRC values. This is useful if one
|
|
sends a "train of packets" which include a CRC so far. This detects both
|
|
errors in one packet but also missing packets, or injected packages.
|
|
|
|
Another trick one can do is change the polynome or the reverse flag during
|
|
the process. This makes it harder to imitate.
|
|
|
|
Furthermore the class allows to add values in single steps and continue too.
|
|
|
|
Finally the class version gives more readable code (imho) as the parameters
|
|
are explicitly set.
|
|
|
|
|
|
**Note** the classes have same names as the static functions, except the class
|
|
is UPPER case. So CRC8 is a class and **crc8()** is the function.
|
|
|
|
Deeper tech info -https://en.wikipedia.org/wiki/Cyclic_redundancy_check
|
|
and many other websites.
|
|
|
|
|
|
## Interface CRC classes
|
|
|
|
These interfaces are very similar for CRC8, CRC16, CRC32 and CRC64 class.
|
|
The only difference is the data type for polynome, start- and end-mask,
|
|
and the returned CRC.
|
|
|
|
Use **\#include "CRC8.h"**
|
|
|
|
- **CRC8()** Constructor
|
|
- **void reset()** set all internals to constructor defaults.
|
|
- **void restart()** reset internal CRC and count only; reuse values for other
|
|
e.g polynome, XOR masks and reverse flags.
|
|
- **void setPolynome(polynome)** set polynome, note reset sets a default polynome.
|
|
- **void setStartXOR(start)** set start-mask, default 0.
|
|
- **void setEndXOR(end)** set end-mask, default 0.
|
|
- **void setReverseIn(bool reverseIn)** reverse the bit pattern of input data (MSB vs LSB).
|
|
- **void setReverseOut(bool reverseOut)** reverse the bit pattern of CRC (MSB vs LSB).
|
|
- **void add(value)** add a single value to CRC calculation.
|
|
- **void add(array, uint32_t length)** add an array of values to the CRC.
|
|
In case of a warning/error use casting to (uint8_t \*).
|
|
- **uint8_t getCRC()** returns CRC calculated so far. This allows to check the CRC of
|
|
a really large stream at intermediate moments, e.g. to link multiple packets.
|
|
- **uint32_t count()** returns number of values added so far. Default 0.
|
|
|
|
|
|
### Example snippet
|
|
|
|
A minimal usage only needs:
|
|
- the constructor, the add() function and the getCRC() function.
|
|
|
|
```cpp
|
|
#include "CRC32.h"
|
|
...
|
|
|
|
CRC32 crc;
|
|
...
|
|
while (Serial.available())
|
|
{
|
|
int c = Serial.read();
|
|
crc.add(c);
|
|
}
|
|
Serial.println(crc.getCRC());
|
|
```
|
|
|
|
|
|
## Interface static functions
|
|
|
|
Use **\#include "CRC.h"**
|
|
|
|
Most functions have a default polynome, same start and end masks, and default there is no reversing.
|
|
However these parameters allow one to tweak the CRC in all aspects known.
|
|
In all the examples encountered the reverse flags were set both to false or both to true.
|
|
For flexibility both parameters are kept available.
|
|
|
|
- **uint8_t crc8(array, length, polynome = 0xD5, start = 0, end = 0, reverseIn = false, reverseOut = false)** idem with default polynome.
|
|
- **uint16_t crc16(array, length, polynome = 0xA001, start = 0, end = 0, reverseIn = false, reverseOut = false)** idem with default polynome.
|
|
- **uint16_t crc16-CCITT(array, length)** fixed polynome **0x1021**, non zero start / end masks.
|
|
- **uint32_t crc32(array, length, polynome = 0x04C11DB7, start = 0, end = 0, reverseIn = false, reverseOut = false)** idem with default polynome.
|
|
- **uint64_t crc64(array, length, polynome, start, end, reverseIn, reverseOut)** - experimental version, no reference found except on Wikipedia.
|
|
|
|
Note these functions are limited to one call per block of data. For more flexibility use the classes.
|
|
|
|
|
|
## Operational
|
|
|
|
See examples.
|
|
|
|
|
|
## Links
|
|
|
|
- https://en.wikipedia.org/wiki/Cyclic_redundancy_check - generic background.
|
|
- https://crccalc.com/ - online CRC calculator to verify.
|
|
|
|
|
|
## Future
|
|
|
|
- extend examples.
|
|
- table versions for performance? (performance - memory discussion)
|
|
- example showing multiple packages of data linked by their CRC.
|
|
- stream version - 4 classes class?
|
|
- setCRC(value) to be able to pick up where one left ?
|
|
- getters, getPolynome() etc?
|
|
-
|
|
|
|
|
|
#### Exotic CRC's ?
|
|
|
|
- **CRC1()** // parity :)
|
|
- **CRC4(array, length, polynome, start, end, reverseIn, reverseOut)** nibbles?
|
|
- default polynome 0x03
|
|
|
|
|
|
#### Magic \#defines for "common" polynomes? verify ?
|
|
|
|
- \#define CRC_ISO64 0x000000000000001B
|
|
- \#define CRC_ECMA64 0x42F0E1EBA9EA3693
|
|
|