nRF52832 i2c communication with LIS3DH accelerometer

RE: nRF52832 i2c communication with LIS3DH accelerometer

augustopeterle — Mon, 30 Sep 2019 18:37:25 GMT

I tried now Debug mode and Release mode, but nothing change.

Thanks for reply!

RE: nRF52832 i2c communication with LIS3DH accelerometer

Patrick — Mon, 30 Sep 2019 18:05:47 GMT

What compiler optimization level are you using? Release or debug mode? Playing with those settings may be able to help some but I have no idea by how much.

RE: nRF52832 i2c communication with LIS3DH accelerometer

augustopeterle — Mon, 30 Sep 2019 17:36:20 GMT

I had success at reading with this function. I read two registers of OUT_X, but I still spent 13500 CPU cycles to receive those 2 registers data.

With 13500 cpu cycles, the maximum frequency is 4.7KHz.

I don't know why my function is too slow. Do you have any suggest ?

Thanks for reply.

uint8_t dado[] = {0x0, 0x0};
uint32_t c_start = DWT->CYCCNT;
i2c_read(0x19,LIS3DH_OUT_X_L|0x80,dado,2);
uint32_t c_stop = DWT->CYCCNT;

RE: nRF52832 i2c communication with LIS3DH accelerometer

Patrick — Mon, 30 Sep 2019 13:20:18 GMT

When requesting multiple bits from the LIS3DH you need to make sure you are requesting the correct sub-address. See this excerpt from the datasheet:

In order to read multiple bytes, it is necessary to assert the most significant bit of the subaddress
field. In other words, SUB(7) must be equal to 1 while SUB(6-0) represents the
address of first register to be read.

If you want to read registers starting at OUT_X_L you need to set bit 7 to 1, ie, 0x28 |= 0x40.

RE: nRF52832 i2c communication with LIS3DH accelerometer

bjorn-spockeli — Mon, 30 Sep 2019 13:09:24 GMT

This is using the driver found at https://github.com/IOsonata/IOsonata/tree/master/src/sensors ?

RE: nRF52832 i2c communication with LIS3DH accelerometer

Nguyen Hoan Hoang — Mon, 30 Sep 2019 12:44:56 GMT

There are many sensors implementations using that library for your reference. https://github.com/IOsonata/IOsonata/tree/master/src/sensors

All the read/write register functions are taken care of either spi or i2c. All you need to do is to concentrate on the sensors itself rather than spent time on the low level.

RE: nRF52832 i2c communication with LIS3DH accelerometer

augustopeterle — Mon, 30 Sep 2019 12:40:40 GMT

I tried this. In this case the CPU uses around 13000 cycles, but I always receive zero in the 2 positions of dado array. Did I do anything wrong ?

Thanks for reply.

uint8_t dado[] = {0x0, 0x0};
uint32_t c_start = DWT->CYCCNT;
i2c_read(0x19,LIS3DH_OUT_X_L,&dado,2);
uint32_t c_stop = DWT->CYCCNT;

RE: nRF52832 i2c communication with LIS3DH accelerometer

augustopeterle — Mon, 30 Sep 2019 12:38:11 GMT

Yes, I'm using 400KHz.

I've never used this library, I'll spent a little time studying this.

Thanks!

RE: nRF52832 i2c communication with LIS3DH accelerometer

augustopeterle — Mon, 30 Sep 2019 12:36:55 GMT

Hi,

I'm reading just one byte at time. I read OUT_X_L and after OUT_X_H.

I tried to read 2 bytes but in this case I always receive zero em both registers.

Thanks for reply.

RE: nRF52832 i2c communication with LIS3DH accelerometer

bjorn-spockeli — Mon, 30 Sep 2019 12:32:52 GMT

As Patrick has pointed out it will be faster to read the two registers at the same time, i.e. sending the address of the register you want to start reading from and then reading the number of bytes you need. If you are doing this, then the only thing you can adjust is the frequency i think.

RE: nRF52832 i2c communication with LIS3DH accelerometer

Nguyen Hoan Hoang — Sun, 29 Sep 2019 02:43:38 GMT

Have tried to change the frequency ? The i2c data rate can be set up to 400kbps which is approx 40KB/s transfer rate.

You may try this driver. It's more efficient tha the sdk. https://github.com/IOsonata/IOsonata/blob/master/ARM/Nordic/src/i2c_nrf5x.cpp

usage example https://github.com/IOsonata/IOsonata/blob/master/exemples/i2c/i2c_master_slave.cpp

RE: nRF52832 i2c communication with LIS3DH accelerometer

Patrick — Sat, 28 Sep 2019 18:25:37 GMT

Are you reading the two registers independently (read x_h, read x_l) or are you requesting them in one read command (requesting two bytes during read)?