added USLP example

README.md

@@ -54,27 +54,25 @@ from spacepackets.util import get_printable_data_string, PrintFormats
 
 
 def main():
-  ping_cmd = PusTelecommand(
-    service=17,
-    subservice=1,
-    apid=0x01
-  )
-  cmd_as_bytes = ping_cmd.pack()
-  print_string = get_printable_data_string(print_format=PrintFormats.HEX, data=cmd_as_bytes)
-  print(f'Ping telecommand [17,1]: {print_string}')
-
-  ping_reply = PusTelemetry(
-    service=17,
-    subservice=2,
-    apid=0x01
-  )
-  tm_as_bytes = ping_reply.pack()
-  print_string = get_printable_data_string(print_format=PrintFormats.HEX, data=tm_as_bytes)
-  print(f'Ping reply [17,2]: {print_string}')
+    print("-- PUS packet examples --")
+    ping_cmd = PusTelecommand(service=17, subservice=1, apid=0x01)
+    cmd_as_bytes = ping_cmd.pack()
+    print_string = get_printable_data_string(
+        print_format=PrintFormats.HEX, data=cmd_as_bytes
+    )
+    print(f"Ping telecommand [17,1]: {print_string}")
+
+    ping_reply = PusTelemetry(service=17, subservice=2, apid=0x01)
+    tm_as_bytes = ping_reply.pack()
+    print_string = get_printable_data_string(
+        print_format=PrintFormats.HEX, data=tm_as_bytes
+    )
+    print(f"Ping reply [17,2]: {print_string}")
 
 
 if __name__ == "__main__":
-  main()
+    main()
+
 ```
 
 ## CCSDS Space Packet
@@ -87,19 +85,84 @@ from spacepackets.util import get_printable_data_string, PrintFormats
 
 
 def main():
+    print("-- Space Packet examples --")
     spacepacket_header = SpacePacketHeader(
+        packet_type=PacketTypes.TC, apid=0x01, source_sequence_count=0, data_length=0
+    )
+    header_as_bytes = spacepacket_header.pack()
+    print_string = get_printable_data_string(
+        print_format=PrintFormats.HEX, data=header_as_bytes
+    )
+    print(f"Space packet header: {print_string}")
+
+
+if __name__ == "__main__":
+    main()
+
+```
+
+## USLP Frames
+
+This example shows how to generate a simple variable length USLP frame containing a simple
+space packet
+
+```py
+from spacepackets.uslp.header import (
+    PrimaryHeader,
+    SourceOrDestField,
+    ProtocolCommandFlag,
+    BypassSequenceControlFlag,
+)
+from spacepackets.uslp.frame import (
+    TransferFrame,
+    TransferFrameDataField,
+    TfdzConstructionRules,
+    UslpProtocolIdentifier,
+)
+from spacepackets.ccsds.spacepacket import SpacePacketHeader, PacketTypes, SequenceFlags
+
+SPACECRAFT_ID = 0x73
+
+
+def main():
+    print("-- USLP frame example --")
+    frame_header = PrimaryHeader(
+        scid=SPACECRAFT_ID,
+        map_id=0,
+        vcid=1,
+        src_dest=SourceOrDestField.SOURCE,
+        frame_len=0,
+        vcf_count_len=0,
+        op_ctrl_flag=False,
+        prot_ctrl_cmd_flag=ProtocolCommandFlag.USER_DATA,
+        bypass_seq_ctrl_flag=BypassSequenceControlFlag.SEQ_CTRLD_QOS,
+    )
+    data = bytearray([1, 2, 3, 4])
+    # Wrap the data into a space packet
+    space_packet_wrapper = SpacePacketHeader(
         packet_type=PacketTypes.TC,
-        apid=0x01,
+        sequence_flags=SequenceFlags.UNSEGMENTED,
+        apid=SPACECRAFT_ID,
+        data_length=len(data) - 1,
         source_sequence_count=0,
-        data_length=0
     )
-    header_as_bytes = spacepacket_header.pack()
-    print_string = get_printable_data_string(print_format=PrintFormats.HEX, data=header_as_bytes)
-    print(f'Space packet header: {print_string}')
+    tfdz = space_packet_wrapper.pack() + data
+    tfdf = TransferFrameDataField(
+        tfdz_cnstr_rules=TfdzConstructionRules.VpNoSegmentation,
+        uslp_ident=UslpProtocolIdentifier.SPACE_PACKETS_ENCAPSULATION_PACKETS,
+        tfdz=tfdz,
+    )
+    var_frame = TransferFrame(header=frame_header, tfdf=tfdf)
+    var_frame_packed = var_frame.pack()
+    print(
+        f"USLP variable length frame without FECF, and Operation Control Field containing a "
+        f"simple space packet: {var_frame_packed.hex(sep=',')}"
+    )
 
 
 if __name__ == "__main__":
     main()
+
 ```
 
 # Tests
@@ -116,4 +179,3 @@ provided that `pytest` and `coverage` were installed with
 ```sh
 python3 -m pip install coverage pytest
 ```
-

examples/example_pus.py

@@ -4,6 +4,7 @@
 
 
 def main():
+    print("-- PUS packet examples --")
     ping_cmd = PusTelecommand(service=17, subservice=1, apid=0x01)
     cmd_as_bytes = ping_cmd.pack()
     print_string = get_printable_data_string(

examples/example_spacepacket.py

@@ -3,6 +3,7 @@
 
 
 def main():
+    print("-- Space Packet examples --")
     spacepacket_header = SpacePacketHeader(
         packet_type=PacketTypes.TC, apid=0x01, source_sequence_count=0, data_length=0
     )

examples/example_uslp.py

@@ -0,0 +1,55 @@
+from spacepackets.uslp.header import (
+    PrimaryHeader,
+    SourceOrDestField,
+    ProtocolCommandFlag,
+    BypassSequenceControlFlag,
+)
+from spacepackets.uslp.frame import (
+    TransferFrame,
+    TransferFrameDataField,
+    TfdzConstructionRules,
+    UslpProtocolIdentifier,
+)
+from spacepackets.ccsds.spacepacket import SpacePacketHeader, PacketTypes, SequenceFlags
+
+SPACECRAFT_ID = 0x73
+
+
+def main():
+    print("-- USLP frame example --")
+    frame_header = PrimaryHeader(
+        scid=SPACECRAFT_ID,
+        map_id=0,
+        vcid=1,
+        src_dest=SourceOrDestField.SOURCE,
+        frame_len=0,
+        vcf_count_len=0,
+        op_ctrl_flag=False,
+        prot_ctrl_cmd_flag=ProtocolCommandFlag.USER_DATA,
+        bypass_seq_ctrl_flag=BypassSequenceControlFlag.SEQ_CTRLD_QOS,
+    )
+    data = bytearray([1, 2, 3, 4])
+    # Wrap the data into a space packet
+    space_packet_wrapper = SpacePacketHeader(
+        packet_type=PacketTypes.TC,
+        sequence_flags=SequenceFlags.UNSEGMENTED,
+        apid=SPACECRAFT_ID,
+        data_length=len(data) - 1,
+        source_sequence_count=0,
+    )
+    tfdz = space_packet_wrapper.pack() + data
+    tfdf = TransferFrameDataField(
+        tfdz_cnstr_rules=TfdzConstructionRules.VpNoSegmentation,
+        uslp_ident=UslpProtocolIdentifier.SPACE_PACKETS_ENCAPSULATION_PACKETS,
+        tfdz=tfdz,
+    )
+    var_frame = TransferFrame(header=frame_header, tfdf=tfdf)
+    var_frame_packed = var_frame.pack()
+    print(
+        f"USLP variable length frame without FECF, and Operation Control Field containing a "
+        f"simple space packet: {var_frame_packed.hex(sep=',')}"
+    )
+
+
+if __name__ == "__main__":
+    main()

spacepackets/ccsds/spacepacket.py

@@ -40,7 +40,8 @@ def __init__(
             than 11 bits, deciaml 2074 or hex 0x7ff
         :param source_sequence_count: Sequence counter, should not be larger than 0x3fff or
             decimal 16383
-        :param data_length: Should not be largen than 65535 bytes
+        :param data_length: Contains a length count C that equals one fewer than the length of the
+            packet data field. Should not be larger than 65535 bytes
         :param packet_version:
         :param secondary_header_flag:
         :param sequence_flags:

spacepackets/uslp/frame.py

@@ -328,9 +328,9 @@ def __init__(
         self,
         header: FrameHeaderT,
         tfdf: TransferFrameDataField,
-        insert_zone: Optional[bytes],
-        op_ctrl_field: Optional[bytes],
-        fecf: Optional[bytes],
+        insert_zone: Optional[bytes] = None,
+        op_ctrl_field: Optional[bytes] = None,
+        fecf: Optional[bytes] = None,
     ):
         self.header = header
         self.tfdf = tfdf