Acknowledgment giving wrong value

[timeb]

I was trying to follow the LoRa Nano-Gateway example in the docs https://docs.pycom.io/pycom_esp32/pycom_esp32/tutorial/includes/lora-nano-gateway.html. In the gateway code there is ack_pkg = struct.pack(_LORA_PKG_ACK_FORMAT, device_id, 1, 200)
lora_sock.send(ack_pkg). So, I should get an acknowledgment on the message sending node. I am not getting the acknowledgment. To debug I used a print statement and printed print(ack) on the node sending the data. Instead of getting 200, print(ack) produces 161. Why does the value of the ack change? I believe this problem is the cause for not receiving the acknowledgment.

[timeb]

while (True):
recv_pkg = lora_sock.recv(512)
time.sleep(0.2)

if(len(recv_pkg) > 13):
    print(recv_pkg)
    recv_pkg_len = recv_pkg[12]
    # unpack the message based on protocol definition
    dest_addr,  src_addr, pkg_len, msg = struct.unpack(_LORA_PKG_FORMAT % recv_pkg_len,  recv_pkg) 
    if(dest_addr==SRC_ADDR):
        ack_pkg = struct.pack(_LORA_ACK_FORMAT, src_addr, SRC_ADDR, 1, 200)
        lora_sock.send(ack_pkg)
            else:
                    print("Message lost")

[timeb]

while (True):
recv_pkg = lora_sock.recv(512)
time.sleep(0.2)

if(len(recv_pkg) > 13):
    recv_pkg_len = recv_pkg[12]
    # unpack the message based on protocol definition
    dest_addr,  src_addr, sink_addr, pkg_len, msg = struct.unpack(_LORA_PKG_FORMAT % recv_pkg_len,  recv_pkg) 
    # Check whether it is final destination(Sink address) for message
    if(dest_addr==SRC_ADDR and sink_addr == NULL_ADDR):
        print("Src_addr: %s \t Pkg:  %s" %(src_addr,msg))
        ack_pkg = struct.pack(_LORA_ACK_FORMAT, DST_ADDR,  SRC_ADDR,  1, 200)
        lora_sock.send(ack_pkg)
        waiting_ack = False

[timeb]

@livius

while True:
pkg = struct.pack(_LORA_PKG_FORMAT %len(msg), DEST_MAC_ADDR,
SRC_MAC_ADDR, SINK_MAC_ADDR,len(msg), msg)
lora_sock.send(pkg)

    waiting_ack = True
    while(waiting_ack):
        # if a message of the size of acknowledge message is received
        if(len(recv_ack) > 0):
            to_addr,  from_addr , pkg_len, ack = struct.unpack(_LORA_ACK_FORMAT, recv_ack)
            if(to_addr == SRC_MAC_ADDR and from_addr == DEST_MAC_ADDR):
                if(ack == 200):
                    waiting_ack=False
                    print("Ack Received from: %s"%DEST_MAC_ADDR)
                else:             
                    waiting_ack = False
                    print("Message Failed")
            elif(to_addr == SRC_MAC_ADDR and from_addr == SINK_MAC_ADDR):
                if(ack == 200):
                    waiting_ack = False
            
            else:
                waiting_ack = False
                print("Ack Error") 
    time.sleep(5)

[livius]

@timeb
You must show more info, format used for pack and unpack
Data used for call function arguments
also data send and what you recived

[timeb]

I am focusing on this part which belongs to the Node code as given in the docs. The thing is once recv_ack is unpacked and the following two conditions should be tested for the arrival of an acknowledgment.
if(device_id == DEVICE_ID):
if(ack == 200)

So, in my case I don't receive the acknowledgment and I tried to debug it using print after unpacking then I did print(ack) but the value I get is 161 which is not equal to 200 and then I don't receive the acknowledgment. What could have possibly happened?

waiting_ack = True
while(waiting_ack):
recv_ack = lora_sock.recv(256)

    if (len(recv_ack) > 0):
        device_id, pkg_len, ack = struct.unpack(_LORA_PKG_ACK_FORMAT, recv_ack)
        if (device_id == DEVICE_ID):
            if (ack == 200):
                waiting_ack = False
                # If the uart = machine.UART(0, 115200) and os.dupterm(uart) are set in the boot.py this print should appear in the serial port
                print("ACK")
            else:
                waiting_ack = False
                # If the uart = machine.UART(0, 115200) and os.dupterm(uart) are set in the boot.py this print should appear in the serial port
                print("Message Failed")

time.sleep(5)