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MbedCRC< polynomial, width, mode_limit > Class Template Reference
[MbedCRC class]
CRC object provides CRC generation through hardware or software. More...
#include <MbedCRC.h>
Public Member Functions | |
| MbedCRC (uint32_t initial_xor, uint32_t final_xor, bool reflect_data, bool reflect_remainder) | |
| Lifetime of CRC object. | |
| int32_t | compute (const void *buffer, crc_data_size_t size, uint32_t *crc) |
| Compute CRC for the data input Compute CRC performs the initialization, computation and collection of final CRC. | |
| int32_t | compute_partial (const void *buffer, crc_data_size_t size, uint32_t *crc) |
| Compute partial CRC for the data input. | |
| int32_t | compute_partial_start (uint32_t *crc) |
| Compute partial start, indicate start of partial computation. | |
| int32_t | compute_partial_stop (uint32_t *crc) |
| Get the final CRC value of partial computation. | |
Static Public Member Functions | |
| static constexpr uint32_t | get_polynomial () |
| Get the current CRC polynomial. | |
| static constexpr uint8_t | get_width () |
| Get the current CRC width. | |
Detailed Description
template<uint32_t polynomial = POLY_32BIT_ANSI, uint8_t width = 32, CrcMode mode_limit = CrcMode::HARDWARE>
class mbed::MbedCRC< polynomial, width, mode_limit >
CRC object provides CRC generation through hardware or software.
CRC sums can be generated using three different methods: hardware, software ROM tables and bitwise computation. The mode used is normally selected automatically based on required polynomial and hardware capabilities. Any polynomial in standard form (`x^3 + x + 1`) can be used for computation, but custom ones can affect the performance.
First choice is the hardware mode. The supported polynomials are hardware specific, and you need to consult your MCU manual to discover them. Next, ROM polynomial tables are tried (you can find list of supported polynomials here crc_polynomial). If the selected configuration is supported, it will accelerate the software computations. If ROM tables are not available for the selected polynomial, then CRC is computed at run time bit by bit for all data input.
If desired, the mode can be manually limited for a given instance by specifying the mode_limit template parameter. This might be appropriate to ensure a table is not pulled in for a non-speed-critical CRC, or to avoid the hardware set-up overhead if you know you will be calling `compute` with very small data sizes.
- Note:
- Synchronization level: Thread safe
- Template Parameters:
-
polynomial CRC polynomial value in hex width CRC polynomial width mode_limit Maximum amount of acceleration to use
Example: Compute CRC data
#include "mbed.h" int main() { MbedCRC<POLY_32BIT_ANSI, 32> ct; char test[] = "123456789"; uint32_t crc = 0; printf("\nPolynomial = 0x%lx Width = %d \n", ct.get_polynomial(), ct.get_width()); ct.compute((void *)test, strlen((const char*)test), &crc); printf("The CRC of data \"123456789\" is : 0x%lx\n", crc); return 0; }
Example: Compute CRC with data available in parts
#include "mbed.h" int main() { MbedCRC<POLY_32BIT_ANSI, 32> ct; char test[] = "123456789"; uint32_t crc = 0; printf("\nPolynomial = 0x%lx Width = %d \n", ct.get_polynomial(), ct.get_width()); ct.compute_partial_start(&crc); ct.compute_partial((void *)&test, 4, &crc); ct.compute_partial((void *)&test[4], 5, &crc); ct.compute_partial_stop(&crc); printf("The CRC of data \"123456789\" is : 0x%lx\n", crc); return 0; }
Definition at line 148 of file MbedCRC.h.
Constructor & Destructor Documentation
| MbedCRC | ( | uint32_t | initial_xor, |
| uint32_t | final_xor, | ||
| bool | reflect_data, | ||
| bool | reflect_remainder | ||
| ) |
Lifetime of CRC object.
- Parameters:
-
initial_xor Initial value/seed to Xor final_xor Final Xor value reflect_data reflect_remainder
- Note:
- Default constructor without any arguments is valid only for supported CRC polynomials. :: crc_polynomial_t MbedCRC <POLY_7BIT_SD, 7> ct; --- Valid POLY_7BIT_SD MbedCRC <0x1021, 16> ct; --- Valid POLY_16BIT_CCITT MbedCRC <POLY_16BIT_CCITT, 32> ct; --- Invalid, compilation error MbedCRC <POLY_16BIT_CCITT, 32> ct (i,f,rd,rr) Constructor can be used for not supported polynomials MbedCRC<POLY_16BIT_CCITT, 16> sd(0, 0, false, false); Constructor can also be used for supported polynomials with different initial/final/reflect values
Member Function Documentation
| int32_t compute | ( | const void * | buffer, |
| crc_data_size_t | size, | ||
| uint32_t * | crc | ||
| ) |
| int32_t compute_partial | ( | const void * | buffer, |
| crc_data_size_t | size, | ||
| uint32_t * | crc | ||
| ) |
Compute partial CRC for the data input.
CRC data if not available fully, CRC can be computed in parts with available data.
In case of hardware, intermediate values and states are saved by hardware. Mutex locking is used to serialize access to hardware CRC.
In case of software CRC, previous CRC output should be passed as argument to the current compute_partial call. Please note the intermediate CRC value is maintained by application and not the driver.
- Precondition:
- : Call `compute_partial_start` to start the partial CRC calculation.
- Postcondition:
- : Call `compute_partial_stop` to get the final CRC value.
- Parameters:
-
buffer Data bytes size Size of data crc CRC value is intermediate CRC value filled by API.
- Returns:
- 0 on success or a negative error code on failure
- Note:
- : CRC as output in compute_partial is not final CRC value, call `compute_partial_stop` to get final correct CRC value.
| int32_t compute_partial_start | ( | uint32_t * | crc ) |
Compute partial start, indicate start of partial computation.
This API should be called before performing any partial computation with compute_partial API.
- Parameters:
-
crc Initial CRC value set by the API
- Returns:
- 0 on success or a negative in case of failure
- Note:
- : CRC is an out parameter and must be reused with compute_partial and `compute_partial_stop` without any modifications in application.
| int32_t compute_partial_stop | ( | uint32_t * | crc ) |
Get the final CRC value of partial computation.
CRC value available in partial computation is not correct CRC, as some algorithms require remainder to be reflected and final value to be XORed This API is used to perform final computation to get correct CRC value.
- Parameters:
-
crc CRC result
- Returns:
- 0 on success or a negative in case of failure.
| static constexpr uint32_t get_polynomial | ( | ) | [static] |
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