Serial Port Protocol
This section presents the Serial Port Protocol (SPP) of the NGHam [1]. It is a variation intended to be used over serial communications between radio and computer.
Overview
This chapter describes the protocol used to transfer data and commands between the transceiver and the serial port host.
Packet Fields
In the diagram below, the fields of the SPP packets are illustrated.
Fig. Format of a NGHam SPP packet.
The packet fields are better described in the table below.
Name |
Size (Byte) |
Notes |
|---|---|---|
Star tag |
1 |
Fixed as ‘$’. |
CRC Size |
2 |
16-bit CRC-CCITT (start=0xFFFF, polynomial=0x1021 reversed, Xorout=0xFFFF). Notice the use of little endian, as everything on this layer and up use little endian. CRC is calculated of everything except start tag and CRC itself. |
Payload type |
1 |
0x00=RF receive packet, 0x01=RF transmit packet, 0x02=Local packet, 0x03=Command. |
Payload length |
1 |
Length of payload field. |
Payload |
n |
This is the actual payload specified by the payload type. |
Next, there is a description of the fields of each SPP type of packet.
RF RX Packet
Data received from RF link (from radio to host). Length from 4 to 223. The table below describes what is put into the payload of the general packet format.
Name |
Size (Byte) |
Notes |
|---|---|---|
Time of hour in microseconds |
4 |
Local time of hour timestamp of the incoming packet. Wraps from 3599999999 (one step before 3600 seconds) to 0. N/A-value is 0xFFFFFFFF. |
Noise floor |
1 |
Subtract 200 to get dBm. Eg. 0x50 = -120 dBm. N/A is 0xFF. |
RSSI |
1 |
Same as above. |
Symbol errors |
1 |
Number of corrected Reed Solomon symbols. |
Flags |
1 |
Bit 0: NGHam extension enabled. If this bit is set, the data field is a valid NGHam extension packet. |
Data |
n-8 |
BReceived data. |
RF TX Packet
Data to be transmitted on RF link (from host to radio). Length from 1 to 220. The table below describes what is put into the payload of the general packet format.
Name |
Size (Byte) |
Notes |
|---|---|---|
Flags |
1 |
Bit 0: NGHam extension enabled flag. |
Data |
n-1 B |
Data to be transmitted. |
Local Packet
Packet generated by the radio (not received over the air, from radio to host). For example a status report. The table below describes what is put into the payload of the general packet format.
Name |
Size (Byte) |
Notes |
|---|---|---|
Flags |
1 |
Bit 0: NGHam extension enabled flag. |
Data |
n-1 B |
Data to be transmitted. |
Command (CMD) Packet
This type of packet is used to enter commands. On the Owl VHF, this command will do the same as typing into the command-line interpreter, except the commands and replies are not terminated by LF/CR/CRLF. The table below describes what is put into the payload of the general packet format.
Name |
Size (Byte) |
Notes |
|---|---|---|
Command |
n B |
Non-terminated command, as for example “FREQ 144800000”. |