Establish a i2c communication using DeviceRead and WL?

Questions
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1

Hi,
I can read in 10 bytes from a device object “enc” by DeviceRead(enc,10). The first two bytes represent an unsigned 16-bit integer, the next four a signed 32-bit integer and the rest are bytes.

Is there a function to read these integers directly instead of reading the bytes and then converting them to integers in Mathematica?
Something like BinaryRead[stream, {“type1”,“type2”,…}] works for streams.

Is there a function in Mathematica to convert 4 bytes to a signed integer?
Thanks,
Laszlo

2

Laszlo,

DeviceRead and DeviceReadList take the same arguments as BinaryRead, however, the device driver needs to support the format you want.

DeviceRead[device,{param1,param,...}]

I do not know the particulars of the device driver you are using. The examples show “Real” and “Integer” as options but others may be supported.

You can convert a list of bytes to another format using the Binary reading functions (making sure you have the correct ByteOrdering):

str = StringToStream[StringJoin[FromCharacterCode[lst]]]
BinaryReadList[str, "Integer32", numberOfIntegers, ByteOrdering -> 1]

Regards,

Neil

3

Hi Neil,
Thanks for your comment.
I’m using Mathematica built-in i2c driver to read the position of an encoder by a Raspberry Pi.
I can see the numbers changing in the output of dat = Dynamic[DeviceRead[81,10]] (*address 0x51, # of bytes=10 *) but I’ve yet to find a way to extract members of dat.
I know that Dynamic[] makes dat visible in the FrontEnd and it is not a List but there must be a way to get to these members.
Any thought?
Laszlo

4

I’m not an expert on the Pi version of Mathematica, but I would think that

dat = DeviceRead[81,10]

should work. You should not assign a variable to a Dynamic in Mathematica if you want to manipulate the bytes. To convince yourself of this do dat //FullForm and you will see that the internal representation is not what you would want.

Regards,

Neil

5

Neil,
Thanks again. I think I’m going the wrong way in my approach. Indeed //FullForm shows that I can’t access the bytes from the FrontEnd. I can go around this in my application,
Regards,
Laszlo