FXLS8471Q - Accelerometer motion detection function example code

Document created by Tomas Vaverka Employee on Jul 25, 2017Last modified by Tomas Vaverka Employee on Apr 3, 2020
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Hi Everyone,


If you are interested in a simple bare metal example code illustrating the use of the accelerometer motion detection function, please find below one of my examples I created for the FXLS8471Q accelerometer while working with the NXP FRDM-KL25Z platform and FRDMSTBC-A8471 board.


The FXLS8471Q is set to detect motion exceeding 315mg for a minimum period of 40 ms on either the X or Y axis. Once an event is triggered, an interrupt will be generated on the INT1 pin:


void FXLS8471Q_Init (void)
FXLS8471Q_WriteRegister(FT_MT_THS_REG, 0x85); // Set threshold to 312.5mg (5 x 62.5mg )
FXLS8471Q_WriteRegister(FF_MT_COUNT_REG, 0x02); // Set debounce timer period to 40ms
FXLS8471Q_WriteRegister(FF_MT_CFG_REG, 0xD8); // Latch enabled, motion detection enabled for X and Y axis

FXLS8471Q_WriteRegister(CTRL_REG4, 0x04); // Motion interrupt enabled
FXLS8471Q_WriteRegister(CTRL_REG5, 0x04); // Route motion interrupt to INT1 - PTD4

FXLS8471Q_WriteRegister(CTRL_REG1, 0x29); // ODR = 12.5Hz, Active mode



In the ISR, only the interrupt flag is cleared and the FF_MT_SRC (0x16) register is read in order to clear the SRC_FFMT flag in the INT_SOURCE register and deassert the INT1 pin, as shown on the screenshot below.


void PORTD_IRQHandler()
PORTD_PCR4 |= PORT_PCR_ISF_MASK; // Clear the interrupt flag
IntSource = FXLS8471Q_ReadRegister(FF_MT_SRC_REG); // Read the FF_MT_SRC register to clear the SRC_FFMT flag in the INT_SOURCE register




Attached you can find the complete source code. If there are any questions regarding this simple example code, please feel free to ask below. 




Original Attachment has been moved to: FRDM-KL25Z-FRDMSTBC-A8471-Motion-detection-using-interrupts.rar

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