MMA8652FC FIFO Buffer

[ands]

Hi, I'm trying to read from the FIFO Buffer off of the MMA8652FC Accelerometer.

I currently have it set up where the Buffer mode is set to be a Fill Buffer and the Watermark is set to 32 samples. I also have F_READ (Fast Read mode) enabled, so that the data I'm reading in is only 8-bits.

I do understand that whenever F_MODE is greater than 0, the OUT_X_MSB (0x01) register becomes the root pointer to XYZ FIFO data.

With this in mind, when I try to read and access the FIFO samples from OUT_X_MSB, it only returns 0x80 96 times. So it's clear I'm accessing the FIFO data improperly, however I cannot figure out why.

Note that I am able to access the data normally with the FIFO buffer disabled

The code I am using to read off of the FIFO is this:

void accel_BufRead(uint8* Data_Ptr){
  uint8 numBytes=96; //96 because I'm reading 32 samples of 8-bit XYZ data thus 32*3=96

  uint8 Write_Buf[1] = {0};
  uint8 *Write_Ptr = &Write_Buf;
  Write_Buf[0] = 0x01;


  I2C_1_MasterWriteBuf(Addr, Write_Ptr, 1, I2C_1_MODE_NO_STOP);//Addr is the slave address, Write_Ptr is the register address, I2C_1_MODE_NO_STOP
                                                               //indicates a mode where it will execute an I2C transfer without a Stop
    while(0u == (I2C_1_MasterStatus() & I2C_1_MSTAT_WR_CMPLT)){} //Check if the write process was successful and completed

  I2C_1_MasterReadBuf(Addr, Data_Ptr, numBytes, I2C_1_MODE_REPEAT_START);//Addr is the slave address, Data_Ptr is where the data will be stored,
                                                                         //numBytes= 96 bytes of data expected to read, I2C_MODE_REPEAT_START 
                                                                         //indicates mode where it will execute an I2C transfer 
                                                                         //by sending a Repeat Start instead of a Start
    while(0u == (I2C_1_MasterStatus() & I2C_1_MSTAT_RD_CMPLT)){} //Check if the read process was successful and completed

    return;
}

[TomasVaverka · Accepted solution]

Hi Andrew,

It is hard to say where the problem might be, but attached you can find my example code I just wrote to test it. Accelerometer setting can be found in the MMA8652FC_Init function.

Here you can see some screenshots illustrating correct behavior.

F_READ = 1, so the data is 8-bits only:

ODR is set to 800Hz, so the FIFO interrupt happens every 40 ms (1.25 ms x 32 samples):

Let me know whether or not this helps, or if you have any other questions.

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct" or “Helpful”. Thank you.

[ands]

Hi Tomas,

Thank you so much for replying to my question. Your sample code made me realize that the read function provided in Cypress' PSoC library just wasn't doing what I needed it to do. So I rewrote their read function and it seems like it is finally properly functioning. Thank you so much! This is the data output I get now.

I polled the INT1 Pin to see if the interrupt was functioning properly and for the most part it is. There are times where it gets a strange signal where it goes low and high and low and high again. Here's a picture of what I'm talking about:

Do you have any ideas of why that's happening? Just to make sure, the only thing I need to clear the interrupt is read the F_STATUS (0x00) register right?

[TomasVaverka]

Hi Andrew,

Glad to see it works now. I would recommend reading the FIFO only, as you can see in my sample code. Then you should not get the second pulse on the INT1 pin.

I hope it helps.

Regards,

Tomas