FXLS8967AF - read FIFO?

[andrewneil]

I don't find the datasheet at all clear on how to read out the values from the FIFO.

Is it necessary to repeatedly read the individual triplets

for each triplet
{
   sensor_comm_read( handle, FXLS896xAF_BUF_X_LSB, 6, data );
}

Or will a single burst read get all the triplets

sensor_comm_read( handle, FXLS896xAF_BUF_X_LSB, number_of_triplets*6, data );

ie, does the auto-increment loop-back from BUF_Z_MSB to BUF_X_LSB so long as there is more data in the FIFO?

[diazmarin09]

Hello andrewneil,

I hope all is great with you. Thank you for using the NXP communities.

The byte order of the output data is programmable via SENS_CONFIG2[LE_BE], and defaults to little-endian mode.

If SENS_CONFIG2[F_READ] = 1, the auto increment mechanism skips over the MSB registers. This operation shortens the output data size from 6 bytes to 3 bytes per XYZ sample.

I do recommend downloading the driver example from the link below and using it as a reference for your design.

Sensor Drivers for NXP Sensors

I hope this information helps.

Regards,

David

[andrewneil]

I'm sorry, that doesn't answer the question at all.

The question is, to read the entire FIFO:

1. can I read the entire FIFO with a single burst read, or
2. must I do multiple burst reads - one for each (X,Y,Z) triplet ?

In other words, what happens in a burst read after reading BUF_Z_MSB (0x11):

• does it "loop-back" to BUF_X_LSB (0x0C), or
• does it carry on to PROD_REV (0x12) ?

I have downloaded the drivers - they do not illustrate this.

[diazmarin09]

Hello andrewneil,

Please accept my apologies for the misunderstanding.

You are correct, should perform multiple burst reading procedures to read the entire buffer.  

Regards,

David

[andrewneil]

@diazmarin09 - should perform multiple burst reading procedures

Really?

As already noted, that Table 20 in the datasheet is very confusing:

https://community.nxp.com/t5/Sensors/FXLS8967AF-Confused-by-quot-Auto-increment-Address-quot/m-p/178...

But I think I've now managed to figure it out:

So a Normal (F_READ=0) burst read of 13 bytes starting at 0x0B should get:

1. BUF_STATUS (0Bh)
2. BUF_X_LSB  (0Ch)
3. BUF_X_MSB  (0Dh)
4. BUF_Y_LSB  (0Eh)
5. BUF_Y_MSB  (0Fh)
6. BUF_Z_LSB  (10h)
7. BUF_Z_MSB  (11h)
8. BUF_X_LSB  (0Ch)
9. BUF_X_MSB  (0Dh)
10. BUF_Y_LSB  (0Eh)
11. BUF_Y_MSB  (0Fh)
12. BUF_Z_LSB  (10h)
13. BUF_Z_MSB  (11h)

Yes ?

Or have I still not understood Table 20 ?

[diazmarin09]

Hello andrewneil,

I know that Table 20 is indeed confusing, but your understanding is correct. I mean, that is the expected registers sequence with the auto-increment feature and F_READ=0.

Regards,

David

[andrewneil]

Good.

So it should require just one burst to read the entire FIFO?

BUF_STATUS[BUF_CNT]  indicates the number of triplets required, so the total burst length required would be six times the BUF_STATUS[BUF_CNT] value ?

I know that Table 20 is indeed confusing

It certainly is!

I will update the other thread on that topic:

https://community.nxp.com/t5/Sensors/FXLS8967AF-Confused-by-quot-Auto-increment-Address-quot/m-p/178...

[diazmarin09]

Hello andrewneil,

BUF_STATUS[BUF_CNT]  indicates the number of triplets required, so the total burst length required would be six times the BUF_STATUS[BUF_CNT] value?

You are correct, my apologies for the confusion. I do appreciate your efforts. 

Regards,

David