This section briefly covers how to capture data from the AI Engine array. For full details please see the python function convert_bytes_to_numpy(). The sample_transaction() method blocks and returns a full AXI payload consisting of all the data received from the AI Engine array. This is different than the transmitting AXI side because the data is captured as an array of bytes with TLAST forming the packet boundary. The format string variable is important for interpreting the byte array appropriately. For this tutorial a cint16 window type was used as the output. The unpack() method interprets the output as an array of int16s (2 bytes each) and then takes the even samples to form the real and imaginary components of the complex vector. These are packed into a single complex data vector.
#Receive byte array from AXI traffic generator slave
payload = self.out0_util.sample_transaction()
#Note: this is a blocking call
formatString = "<"+str(len(payload.data)//2)+"h"
#"h" corresponds to a signed short which is 2 bytes in size. len() returns units of bytes.
upack = struct.unpack(formatString, payload.data)
#take the even numbered samples for real
rvec = upack[0:len(upack):2]
#take the odd numbered samples for imaginary
ivec = upack[1:len(upack):2]
#Reassemble into a complex numpy array
cVec = np.array(rvec) + 1j*np.array(ivec)