G8BPQ Debug Output
Document is under construction! -- July 21, 2025
Some material co-opted from John Wiseman, G8BPQ.
In the FAQ page we have a list of technical-packet documents that are useful starting points for the manual pages on debugging:
FAQ: Technical Packet
Decoding the Monitor Window output
The Monitor window verbosely interprets the packets being sent and received by the node.
There are several key pieces of information displayed and there are some subtleties. This is a list of the data displayed and a key to try to understand it.
- Time-stamp in hours:minutes:seconds
- T or R -- Transmit or Receive -- from the perspective of the node where monitoring is taking place
- AX.25 frame details including:
- originator callsign-ssid for the link (matches the node callsign where monitoring is taking place in the case of transmissions
- destination callsign-ssid for the link (matches the node callsign where monitoring is taking place, in the case of receptions
- digipeater callsigns. There can be up to 7 of them. We usually don't see these in a TARPN world but you might if you monitor APRS or packet zoo channels. If you do receive (R) a
transmission with a digipeater field, there will be a * after the callsign whose transmission you heard.
- port=# port number. This is the radio port being monitored for the data being displayed. Matches the P)orts command response for this node
- < Flags >. This shows bits read from the message being monitored. Flags can be:
- CntrlFld=11 UI -- Unnumbered Info frame -- used for nodes broadcasts, CQs, APRS
- CntrlFld=01 S -- Supervisory frame -- output will have
- CntrlFld=X0 I -- Information xfer --
- more more more
- more more more
Source code for G8BPQ monitor display code
int IntDecodeFrame(MESSAGE * msg, char * buffer, int Stamp, UINT Mask, BOOL APRS)
{
UCHAR * ptr;
int n;
MESSAGE * ADJBUFFER;
UINT Work;
UCHAR CTL;
BOOL PF = 0;
char CRCHAR[3] = " ";
char PFCHAR[3] = " ";
int Port;
int MSGFLAG = 0; //CR and V1 flags
char * Output = buffer;
int HH, MM, SS;
char TR = 'R';
char From[10], To[10];
BOOL Info = 0;
BOOL FRMRFLAG = 0;
int MsgLen = msg->LENGTH;
// GET THE CONTROL BYTE, TO SEE IF THIS FRAME IS TO BE DISPLAYED
n = 8; // MAX DIGIS
ptr = &msg->ORIGIN[6]; // End of Address bit
while ((*ptr & 1) == 0)
{
// MORE TO COME
ptr += 7;
n--;
if (n == 0)
{
return 0; // Corrupt - no end of address bit
}
}
// Reached End of digis
Work = (UINT)&msg->ORIGIN[6];
ptr -= Work; // ptr is now length of digis
MsgLen -= (UINT)ptr;
Work = (UINT)msg;
ptr += Work;
ADJBUFFER = (MESSAGE * )ptr; // ADJBUFFER points to CTL, etc. allowing for digis
CTL = ADJBUFFER->CTL;
if (CTL & PFBIT)
PF = TRUE;
CTL &= ~PFBIT;
if (MUIONLY)
if (CTL != 3)
return 0;
if ((CTL & 1) == 0 || CTL == FRMR || CTL == 3)
{
}
else
{
if (MCOM == 0)
return 0; // Dont do control
}
Port = msg->PORT;
if (Port & 0x80)
{
if (MTX == 0)
return 0; // TRANSMITTED FRAME - SEE IF MTX ON
TR = 'T';
}
Port &= 0x7F;
if (((1 << (Port - 1)) & Mask) == 0) // Check MMASK
return 0;
Stamp = Stamp % 86400; // Secs
HH = Stamp / 3600;
Stamp -= HH * 3600;
MM = Stamp / 60;
SS = Stamp - MM * 60;
Output += sprintf(Output, "%02d:%02d:%02d%c ", HH, MM, SS, TR);
From[ConvFromAX25(msg->ORIGIN, From)] = 0;
To[ConvFromAX25(msg->DEST, To)] = 0;
Output += sprintf(Output, "%s>%s", From, To);
// Display any Digi-Peaters
n = 8; // Max number of digi-peaters
ptr = &msg->ORIGIN[6]; // End of Address bit
while ((*ptr & 1) == 0)
{
// MORE TO COME
From[ConvFromAX25(ptr + 1, From)] = 0;
Output += sprintf(Output, ",%s", From);
ptr += 7;
n--;
if (n == 0)
break;
// See if digi actioned - put a * on last actioned
if (*ptr & 0x80)
{
if (*ptr & 1) // if last address, must need *
*(Output++) = '*';
else
if ((ptr[7] & 0x80) == 0) // Repeased by next?
*(Output++) = '*'; // No, so need *
}
}
Output += sprintf(Output, " Port=%d ", Port);
// Set up CR and PF
CRCHAR[0] = 0;
PFCHAR[0] = 0;
if (msg->DEST[6] & 0x80)
{
if (msg->ORIGIN[6] & 0x80) // Both set, assume V1
MSGFLAG |= VER1;
else
{
MSGFLAG |= CMDBIT;
CRCHAR[0] = ' ';
CRCHAR[1] = 'C';
if (PF) // If FP set
{
PFCHAR[0] = ' ';
PFCHAR[1] = 'P';
}
}
}
else
{
if (msg->ORIGIN[6] & 0x80) // Only Origin Set
{
MSGFLAG |= RESP;
CRCHAR[0] = ' ';
CRCHAR[1] = 'R';
if (PF) // If FP set
{
PFCHAR[0] = ' ';
PFCHAR[1] = 'F';
}
}
else
MSGFLAG |= VER1; // Neither, assume V1
}
if ((CTL & 1) == 0) // I frame
{
int NS = (CTL >> 1) & 7; // ISOLATE RECEIVED N(S)
int NR = (CTL >> 5) & 7;
Info = 1;
Output += sprintf(Output, "", CRCHAR, PFCHAR, NS, NR);
}
else if (CTL == 3)
{
// Un-numbered Information Frame
Output += sprintf(Output, "", CRCHAR);
Info = 1;
}
else if (CTL & 2)
{
// UN Numbered
char SUP[5] = "??";
switch (CTL)
{
case SABM:
strcpy(SUP, "C");
break;
case DISC:
strcpy(SUP, "D");
break;
case DM:
strcpy(SUP, "DM");
break;
case UA:
strcpy(SUP, "UA");
break;
case FRMR:
strcpy(SUP, "FRMR");
FRMRFLAG = 1;
break;
}
Output += sprintf(Output, "<%s%s%s>", SUP, CRCHAR, PFCHAR);
}
else
{
// Super
int NR = (CTL >> 5) & 7;
char SUP[4] = "??";
switch (CTL & 0x0F)
{
case RR:
strcpy(SUP, "RR");
break;
case RNR:
strcpy(SUP, "RNR");
break;
case REJ:
strcpy(SUP, "REJ");
break;
}
Output += sprintf(Output, "<%s%s%s R%d>", SUP, CRCHAR, PFCHAR, NR);
}
if (FRMRFLAG)
Output += sprintf(Output, " %02X %02X %02X", ADJBUFFER->PID, ADJBUFFER->L2DATA[0], ADJBUFFER->L2DATA[1]);
if (Info)
{
// We have an info frame
switch (ADJBUFFER->PID)
{
case 0xF0: // Normal Data
{
char Infofield[257];
char * ptr1 = Infofield;
char * ptr2 = ADJBUFFER->L2DATA;
UCHAR C;
int len;
MsgLen = MsgLen - 23;
if (MsgLen < 0 || MsgLen > 257)
return 0; // Duff
while (MsgLen--)
{
C = *(ptr2++);
if (APRS)
*(ptr1++) = C; // MIC-E needs all chars
else
{
// Convert to printable
C &= 0x7F;
if (C == 13 || C == 10 || C > 31)
*(ptr1++) = C;
}
}
len = ptr1 - Infofield;
Output[0] = ':';
Output[1] = 13;
memcpy(&Output[2], Infofield, len);
Output += (len + 2);
break;
}
case NETROM_PID:
Output = DISPLAY_NETROM(ADJBUFFER, Output, MsgLen);
break;
case IP_PID:
Output += sprintf(Output, " \r");
Output = DISPLAYIPDATAGRAM((IPMSG *)&ADJBUFFER->L2DATA[0], Output, MsgLen);
break;
case ARP_PID:
Output = DISPLAYARPDATAGRAM(&ADJBUFFER->L2DATA[0], Output);
break;
case 8: // Fragmented IP
Output += sprintf(Output, "");
break;
}
}
if (Output[-1] != 13)
Output += sprintf(Output, "\r");
return Output - buffer;
}
// Display NET/ROM data
char * DISPLAY_NETROM(MESSAGE * ADJBUFFER, UCHAR * Output, int MsgLen)
{
char Alias[7]= "";
char Dest[10];
char Node[10];
UCHAR TTL, Index, ID, TXNO, RXNO, OpCode, Flags, Window;
UCHAR * ptr = &ADJBUFFER->L2DATA[0];
if (ADJBUFFER->L2DATA[0] == NODES_SIG)
{
// Display NODES
// If an INP3 RIF (type <> UI) decode as such
if (ADJBUFFER->CTL != 3) // UI
return DisplayINP3RIF(&ADJBUFFER->L2DATA[1], Output, MsgLen - 24);
memcpy(Alias, ++ptr, 6);
ptr += 6;
Output += sprintf(Output, " NODES broadcast from %s\r", Alias);
MsgLen -= 30; //Header, mnemonic and signature length
while(MsgLen > 20) // Entries are 21 bytes
{
Dest[ConvFromAX25(ptr, Dest)] = 0;
ptr +=7;
memcpy(Alias, ptr, 6);
ptr +=6;
strlop(Alias, ' ');
Node[ConvFromAX25(ptr, Node)] = 0;
ptr +=7;
Output += sprintf(Output, " %s:%s via %s qlty=%d\r", Alias, Dest, Node, ptr[0]);
ptr++;
MsgLen -= 21;
}
return Output;
}
// Display normal NET/ROM transmissions
Output += sprintf(Output, " NET/ROM\r ", Alias);
Dest[ConvFromAX25(ptr, Dest)] = 0;
ptr +=7;
Node[ConvFromAX25(ptr, Node)] = 0;
ptr +=7;
TTL = *(ptr++);
Index = *(ptr++);
ID = *(ptr++);
TXNO = *(ptr++);
RXNO = *(ptr++);
OpCode = Flags = *(ptr++);
OpCode &= 15; // Remove Flags
Output += sprintf(Output, "%s to %s ttl %d cct=%02X%02X ", Dest, Node, TTL, Index, ID );
MsgLen -= 20;
switch (OpCode)
{
case L4CREQ:
Window = *(ptr++);
Dest[ConvFromAX25(ptr, Dest)] = 0;
ptr +=7;
Node[ConvFromAX25(ptr, Node)] = 0;
ptr +=7;
Output += sprintf(Output, " w=%d %s at %s", Window, Dest, Node);
if (MsgLen > 38) // BPQ Extended Params
{
short Timeout = (SHORT)*ptr;
Output += sprintf(Output, " t/o %d", Timeout);
}
return Output;
case L4CACK:
if (Flags & L4BUSY) // BUSY RETURNED
return Output + sprintf(Output, " - BUSY");
return Output + sprintf(Output, " w=%d my cct=%02X%02X", ptr[1], TXNO, RXNO);
case L4DREQ:
return Output + sprintf(Output, " ");
case L4DACK:
return Output + sprintf(Output, " ");
case L4INFO:
{
char Infofield[257];
char * ptr1 = Infofield;
UCHAR C;
int len;
Output += sprintf(Output, " ", TXNO, RXNO);
if (Flags & L4BUSY)
*(Output++) = 'B';
if (Flags & L4NAK)
*(Output++) = 'N';
if (Flags & L4MORE)
*(Output++) = 'M';
MsgLen = MsgLen - 23;
if (MsgLen < 0 || MsgLen > 257)
return Output; // Duff
while (MsgLen--)
{
C = *(ptr++);
// Convert to printable
C &= 0x7F;
if (C == 13 || C == 10 || C > 31)
*(ptr1++) = C;
}
len = ptr1 - Infofield;
Output[0] = ':';
Output[1] = 13;
memcpy(&Output[2], Infofield, len);
Output += (len + 2);
}
return Output;
case L4IACK:
Output += sprintf(Output, " ", RXNO);
if (Flags & L4BUSY)
*(Output++) = 'B';
if (Flags & L4NAK)
*(Output++) = 'N';
if (Flags & L4MORE)
*(Output++) = 'M';
return Output;
case 0:
// OPcode zero is used for several things
if (Index == 0x0c && ID == 0x0c) // IP
{
// Output = L3IP(Output);
return Output;
}
if (Index == 0 && ID == 1) // NRR
{
Output += sprintf(Output, " \r");
MsgLen -= 23;
while (MsgLen > 6)
{
Dest[ConvFromAX25(ptr, Dest)] = 0;
if (ptr[7] & 0x80)
Output += sprintf(Output, "%s* ", Dest);
else
Output += sprintf(Output, "%s ", Dest);
ptr +=8;
MsgLen -= 8;
}
return Output;
}
}
Output += sprintf(Output, " ");
return Output;
}
