AWR1642BOOST: Serial data packets, how to convert q-format

Burak Guldogan

Part Number: AWR1642BOOST
Other Parts Discussed in Thread: AWR1642

I am extracting the packets coming from AWR1642 based on the document “mmw Demo Data Structure v0.1”.

I am able detect the magic word (2, 1, 4, 3, 6, 5, 8, 7) and get the range, velocity values. I verified the range and velocity values. But I didn’t understand Q-format for x-y-z values. I think in order to get the azimuth measurements I should use x and y values. ?

How can I convert q-format data to its real value? Is there any relationship between descriptor value and q-format conversion.

The descriptor(4 bytes) in the packets is 2,0,9,0

For instance, from an experiment, I recorded:

X coordinate (2 Bytes): 32 , 0

Y coordinate (2 Bytes): 1 , 2

X coordinate (2 Bytes): 0 , 0

What are real x,y,z values.

Thanks beforehand

Burak

over 7 years ago

0 Akash Gondalia over 7 years ago

TI__Guru 50240 points

Hi Burak,

I believe this question has been answered in this previous thread here: e2e.ti.com/.../624965

Cheers,
Akash

0 Burak Guldogan over 7 years ago in reply to Akash Gondalia

Prodigy 150 points

Hi Akash,

Actually the answer under that link is not clear and also there is no description in the doxygen documents regarding this Q-format. And also I saw in the forum, the same question is asked by some other people and they also could managed to solve it still.

If you could please clarify this issue, maybe with a small example, I appreciate it.

Best,
Burak

0 Francois Charlot over 7 years ago in reply to Burak Guldogan

TI__Mastermind 28077 points

Hi Burak,

The Q format is a way to represent a real number in an integer format that is commonly used when performing signal processing on integer machines.

Representing a real number X in the Q8 format is taking the integer part of (X . 2^8). Note there may be some rounding applied for the LSB to avoid adding an average truncating error of 0.5 LSB.

For example, the xyz values you read were (little endian byte ordering) 32, 513 and 0. These numbers are in Q8 format and translate as real numbers to 0.125, 2.004 and 0.

Thanks,
François.

0 Burak Guldogan over 7 years ago in reply to Francois Charlot

Prodigy 150 points

Hi François,

Thanks for the comments. However, there is something wrong here I think. In my detected object list, there is only one target, which is a strong reflector and in range around 1m just in front of the radar. I am able correctly read the uart data and calculated the range from range index.
Therefore after Q-format conversion, y value should be around 1 not 2.004 as you wrote given the values in my first question.
Could you please check again?

thanks
Burak

0 Herman Stubeda over 7 years ago in reply to Burak Guldogan

Intellectual 290 points

Hi Burak,

This means the Q value is actually 9, not 8. So the conversion will be 513/2^9 = 513/512 = 1.00

The Q value can be found in byte 12 of the "Detected Objects" structure of the UART packet. which is also byte 48 of the total packet.

0 Burak Guldogan over 7 years ago in reply to Herman Stubeda

Prodigy 150 points

Many thanks. Everything is in place now. :)

Burak

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AWR1642BOOST: Serial data packets, how to convert q-format