I'm working on a project that uses the LIS2DH12 accelerometer by ST (product page). I have a couple of questions about it, and as it is quite a common part, I wonder if anyone here knows the answers:

I would like to know if it's possible to activate two interrupts, watermark and overflow, in the same pin. I tried to set them up, enabling latching interrupts in INT1 in CTRL_REG5 and setting both watermark and overflow in CTRL_REG3. When I get a watermark register, I read INT1_SRC, but that returns 0 (I would expect it to return 0x80, interrupt active) and it doesn't clear the interrupts. I don't know if the overflow interrupt ever kicks in, as I can't clear the watermark without reading the FIFO (I would expect that by enabling latching interrupts, I could clear the interrupt by reading INT1_SRC, and then leave the samples unread to trigger the overflow interrupt).

In case somebody is asking why would I do this, I'm a bit paranoid, and don't want to miss an interrupt and end up losing data. Also, I know that I have a second INT pin, but I can't use it at the moment.

//Setup code

// set increment bit so we can write to multiple registers with one SPI command
accel_transfer_buf[0] = LIS2DH12_REG_CTRL_REG0 | LIS2DH12_MULTI_BYTE_RW;  //The register address will increment on every write
accel_transfer_buf[1] = 0x10; //Magic word of the CTRL_REG0, it needs to be that.
accel_transfer_buf[2] = LIS2DH_settings.tempEnabled;
accel_transfer_buf[3] = 0; //Don't write to ctrl1 yet, as that will turn the accelerometer on, do it as the last step in the config
accel_transfer_buf[4] = 0; //Disable High pass filters, see AN5005
accel_transfer_buf[5] = LIS2DH12_BITS_I1_WTM; //Interrupts enabled in INT1 pin: watermark
//Block data update enabled(AN5005), big endian, accelerometer range, normal mode 10bit, 4 wire SPI
accel_transfer_buf[6] = LIS2DH12_BITS_BDU | LIS2DH_settings.accelRange | LIS2DH_settings.HiResMode;
accel_transfer_buf[7] = LIS2DH_settings.fifoEnabled | LIS2DH12_BITS_LIR1; //enable fifo, interrupts latched
accel_transfer_buf[8] = 0; //No int on INT2 pin (it's disconnected anyway). Interrupt polarity set to active High
accel_transfer_buf[9] = 0; //Reference for interrupts


//Later on...
accel_transfer_buf[10] = LIS2DH12_REG_FIFO_CTRL_REG;
accel_transfer_buf[1] = LIS2DH_settings.fifoMode | ((FIFO_THRESHOLD - 1) & 0x1F);


//and finally
accel_transfer_buf[0] = LIS2DH12_REG_CTRL_REG1;
accel_transfer_buf[1] = LIS2DH_settings.accelSampleRate | LIS2DH_settings.HPLPmode | LIS2DH_settings.zAccelEnabled | LIS2DH_settings.yAccelEnabled | LIS2DH_settings.xAccelEnabled;

When I get an interrupt, I do

accel_transfer_buf[0] = LIS2DH12_REG_INT1_SRC | LIS2DH12_READ_REGISTER;
uint32_t errorCode = SPIDRV_MTransferB(spi_handle0, accel_transfer_buf, accel_transfer_buf, 2);
checkErrorCode(errorCode, "DEBUG");
debug_logln(VERBOSE, "Accel Int: 0x%02X", accel_transfer_buf[1]);

And I would expect to get 0x80, but I get 0x00 (and there are no errors in the transfer).

1) Do you know if what I'm doing with the latched interrupts is correct?

2) Do you know if what I'm trying to achieve with the two ints in the same pin is possible?



1 Answer 1


Turns out it can't be done. Only the X/Y/Z High/Low interrupts can be cleared by reading REG_INT1_SRC, the watermark interrupt can't be cleared by other means than by reading from the FIFO.


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