FreeDATA/test/TEST_TX.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Sun Dec 13 13:45:58 2020
@author: DJ2LS
"""

import ctypes
from ctypes import *
import pathlib

import binascii #required for string.to_bytes() function
import sys



def main():
    
    modem = FreeDV() #Load FreeDV Class as "modem"
      
    data = b'HALLO' #byte string which will be send    
       
    modem.Modulate(data) #Call Modulate function, which  modulates data and prints it to the terminal


class FreeDV():
    
    def __init__(self):
        
        self.mode = 12 # define mode

        libname = pathlib.Path().absolute() / "libcodec2.so"
        self.c_lib = ctypes.CDLL(libname) # Load FreeDV shared libary
        
        self.freedv = self.c_lib.freedv_open(self.mode) #Set FreeDV waveform ( 10,11,12 --> DATAC1-3 )

        self.bytes_per_frame = int(self.c_lib.freedv_get_bits_per_modem_frame(self.freedv)/8)  #get bytes per frame from selected waveform
        self.payload_per_frame = self.bytes_per_frame -2 #get frame payload because of 2byte CRC16 checksum
        self.n_tx_modem_samples = self.c_lib.freedv_get_n_tx_modem_samples(self.freedv)*2 #get n_tx_modem_samples which defines the size of the modulation object

    # MODULATION-OUT OBJECT   
    def ModulationOut(self):
        return (c_short * self.n_tx_modem_samples)  ##

    # Pointer for changing buffer data type 
    def FrameBytes(self):
        return (c_ubyte * self.bytes_per_frame)   

    # Modulate function which returns modulated data
    def Modulate(self,data_out):
    
        mod_out = self.ModulationOut()() # new modulation object and get pointer to it
    
        data_list = [data_out[i:i+self.payload_per_frame] for i in range(0, len(data_out), self.payload_per_frame)] # split incomming bytes to size of 30bytes, create a list and loop through it  
        data_list_length = len(data_list)
        for i in range(data_list_length): # LOOP THROUGH DATA LIST
            
            if self.mode < 10: # don't generate CRC16 for modes 0 - 9
            
                buffer = bytearray(self.bytes_per_frame) # use this if no CRC16 checksum is required
                buffer[:len(data_list[i])] = data_list[i] # set buffersize to length of data which will be send
                
            if self.mode >= 10: #generate CRC16 for modes 10-12..
                
                buffer = bytearray(self.payload_per_frame) # use this if CRC16 checksum is required ( DATA1-3)
                buffer[:len(data_list[i])] = data_list[i] # set buffersize to length of data which will be send

                crc = c_ushort(self.c_lib.freedv_gen_crc16(bytes(buffer), self.payload_per_frame))     # generate CRC16
                crc = crc.value.to_bytes(2, byteorder='big') # convert crc to 2 byte hex string
                buffer += crc        # append crc16 to buffer
            
            
            data = self.FrameBytes().from_buffer_copy(buffer) #change data format from bytearray to ctypes.u_byte and copy from buffer to data
     
            self.c_lib.freedv_rawdatatx(self.freedv,mod_out,data) # modulate DATA and safe it into mod_out pointer     

            sys.stdout.buffer.write(mod_out)    # print data to terminal for piping the output to other programs
            sys.stdout.flush() # flushing stdout


main()