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STM8L15x Standard Peripherals Drivers
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Hardware CRC Calculation functions. More...
Functions | |
| void | SPI_CalculateCRCCmd (SPI_TypeDef *SPIx, FunctionalState NewState) |
| Enables or disables the CRC value calculation of the transferred bytes. | |
| uint8_t | SPI_GetCRC (SPI_TypeDef *SPIx, SPI_CRC_TypeDef SPI_CRC) |
| Returns the transmit or the receive CRC register value. | |
| uint8_t | SPI_GetCRCPolynomial (SPI_TypeDef *SPIx) |
| Returns the CRC Polynomial register value. | |
| void | SPI_ResetCRC (SPI_TypeDef *SPIx) |
| Reset the Rx CRCR and Tx CRCR registers. | |
| void | SPI_TransmitCRC (SPI_TypeDef *SPIx) |
| Enables the transmit of the CRC value. | |
Detailed Description
Hardware CRC Calculation functions.
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Hardware CRC Calculation functions
===============================================================================
This section provides a set of functions allowing to manage the SPI CRC hardware
calculation
SPI communication using CRC is possible through the following procedure:
1. Program the Data direction, Polarity, Phase, First Data, Baud Rate Prescaler,
Slave Management, Peripheral Mode and CRC Polynomial values using the SPI_Init()
function.
2. Enable the CRC calculation using the SPI_CalculateCRC() function.
3. Enable the SPI using the SPI_Cmd() function
4. Before writing the last data to the TX buffer, set the CRCNext bit using the
SPI_TransmitCRC() function to indicate that after transmission of the last
data, the CRC should be transmitted.
5. After transmitting the last data, the SPI transmits the CRC. The SPI_CR2_CRCNEXT
bit is reset. The CRC is also received and compared against the SPI_RXCRCR
value.
If the value does not match, the SPI_FLAG_CRCERR flag is set and an interrupt
can be generated when the SPI_IT_ERR interrupt is enabled.
Note:
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- It is advised to don't read the calculate CRC values during the communication.
- When the SPI is in slave mode, be careful to enable CRC calculation only
when the clock is stable, that is, when the clock is in the steady state.
If not, a wrong CRC calculation may be done. In fact, the CRC is sensitive
to the SCK slave input clock as soon as CRCEN is set, and this, whatever
the value of the SPE bit.
- With high bitrate frequencies, be careful when transmitting the CRC.
As the number of used CPU cycles has to be as low as possible in the CRC
transfer phase, it is forbidden to call software functions in the CRC
transmission sequence to avoid errors in the last data and CRC reception.
In fact, CRCNEXT bit has to be written before the end of the transmission/reception
of the last data.
- For high bit rate frequencies, it is advised to use the DMA mode to avoid the
degradation of the SPI speed performance due to CPU accesses impacting the
SPI bandwidth.
- When the STM8L15x are configured as slaves and the NSS hardware mode is
used, the NSS pin needs to be kept low between the data phase and the CRC
phase.
- When the SPI is configured in slave mode with the CRC feature enabled, CRC
calculation takes place even if a high level is applied on the NSS pin.
This may happen for example in case of a multislave environment where the
communication master addresses slaves alternately.
- Between a slave de-selection (high level on NSS) and a new slave selection
(low level on NSS), the CRC value should be cleared on both master and slave
sides in order to resynchronize the master and slave for their respective
CRC calculation.
To clear the CRC, follow the procedure below:
1. Disable SPI using the SPI_Cmd() function
2. Disable the CRC calculation using the SPI_CalculateCRC() function.
3. Enable the CRC calculation using the SPI_CalculateCRC() function.
4. Enable SPI using the SPI_Cmd() function.
Function Documentation
| void SPI_CalculateCRCCmd | ( | SPI_TypeDef * | SPIx, |
| FunctionalState | NewState | ||
| ) |
Enables or disables the CRC value calculation of the transferred bytes.
Definition at line 420 of file stm8l15x_spi.c.
References SPI_struct::CR2, DISABLE, IS_FUNCTIONAL_STATE, SPI1, SPI_Cmd(), and SPI_CR2_CRCEN.
Referenced by SPI_ResetCRC().
| uint8_t SPI_GetCRC | ( | SPI_TypeDef * | SPIx, |
| SPI_CRC_TypeDef | SPI_CRC | ||
| ) |
Returns the transmit or the receive CRC register value.
Definition at line 447 of file stm8l15x_spi.c.
References IS_SPI_CRC, SPI_struct::RXCRCR, SPI_CRC_RX, and SPI_struct::TXCRCR.
| uint8_t SPI_GetCRCPolynomial | ( | SPI_TypeDef * | SPIx | ) |
Returns the CRC Polynomial register value.
Definition at line 487 of file stm8l15x_spi.c.
References SPI_struct::CRCPR.
| void SPI_ResetCRC | ( | SPI_TypeDef * | SPIx | ) |
Reset the Rx CRCR and Tx CRCR registers.
Definition at line 472 of file stm8l15x_spi.c.
References ENABLE, SPI_CalculateCRCCmd(), and SPI_Cmd().
| void SPI_TransmitCRC | ( | SPI_TypeDef * | SPIx | ) |
Enables the transmit of the CRC value.
Definition at line 408 of file stm8l15x_spi.c.
References SPI_struct::CR2, and SPI_CR2_CRCNEXT.