Networking with SIMH

The aim of this quick tutorial is to show how to setup SIMH's networking.

libpcap

By default SIMH supports networking via libpcap. The restrction of this method is that the host machine is unable to communicate with the emulator. Otherwise it's realitivly straight forward. First you need to make sure your binary has networking built in.

Showing host ethernet adapters

By issuing the command 'show xq eth' you will get either a list of adapters, or an error that this version does not support networking.

On the Windows platform it would look something like this:

With networking:

sim> show xq eth
ETH devices:
  0  \Device\NPF_GenericDialupAdapter                   (Adapter for generic dialup and VPN capture)
  1  \Device\NPF_{9E485825-641F-45C3-BC3B-E9DF4DDE520D} (Local Area Connection 4)
  2  \Device\NPF_{279EDB55-7802-44D3-8FA1-15B14452B309} (Local Area Connection)
sim>

Without networking:

sim> show xq eth
ETH devices:
  network support not available in simulator
sim>

Setting the MAC address

To set the MAC address to something other then the default (Which is important if you ever plan on having more then one SIMH device talking to another, say in HecNET) you need to change the MAC address. Remember this needs to be done before you attach the device. The command is simple as all you have to do is type in something to the effect of:

sim> set xq mac=00:00:01:00:00:01

Remember the first half is the vendor code, and the second half is the unique identifier. Do not use all 0's or all FF's it will create major issues on your network.

Attaching the device

Once the host ethernet adapter to bind to has been identified, the MAC address has been configured, you can now attach the emulator to the host network card. you can either specifiy the whole name as listed from the 'xq show dev' command, or use the corresponding number. Thusly:

att xq eth2

And

att xq \Device\NPF_{279EDB55-7802-44D3-8FA1-15B14452B309}

Are identical. You can now boot your emulator and it will have network accesss.

SLiRP

To be done later

Writing your own

According to my old notes, the following code in the sim_ether.c file, replacing the either NON WORKING, or LIB_PCAP sections will produce an exe that will write packets to a directory, and constantly scan another directory for files to 'input' as packets.

#include <fcntl.h>               /*constants defined*/
#include <sys\types.h>
#include <sys\stat.h>            /*constants defined*/
#include <share.h>               /*constants defined*/ 
#include <io.h>

 
//Packet couters for reading/writing
//int Packet;
int PacketR;	//Internal counter to what we have read last.
char Path[255];
char Readpath[255];

/************Helper functions...***************************/

//sopenreadcounter  Opens the readcounter file
//return 1 with the file handle, 0 if the file doesnt exist
//-1 if there was some other error related to the file
int sopenreadcounter(char *path,int *filehndl)
{
//char *filename;
#ifdef DEBUG
printf("sopenreadcounter opening %s\n",path);
#endif
*filehndl=sopen(path,O_RDWR | O_BINARY, SH_DENYRW, S_IREAD | S_IWRITE);

//Check to see if it barfed
if (*filehndl==-1)
	{
#ifdef DEBUG
	printf("sopenreadcounter sopen returned -1 errno %d\n\n",errno);
#endif
	//file doesnt exist!
	if (errno==ENOENT)
		{
#ifdef DEBUG
			printf("sopenreadercount file doesnt exist(ENOENT)!\n");
#endif
		return 0;
		}
	//file is there, but we missed the lock.
	if (errno==EACCES)
		{
			int j=0;
		while(*filehndl==-1)
			{
			*filehndl=sopen(path,O_RDWR|O_BINARY, SH_DENYRW, S_IREAD | S_IWRITE);
#ifdef DEBUG
			printf("\rEACCES on %s fh %d errno %d\t\t%d",path,*filehndl,errno,j);
			//printf("\rEACCES fh %d errno %d\t\t%d",*filehndl,errno,j);
#endif
			Sleep(5);  //jiffy wait..
			j++;
			}
		return 1; //we got the filehandle
		}
	//Some other error.. we're fucked for now let's panic!
	printf("\ndrop out with error sopenreadcounter\n");
	return -1;
	}
return 1;  //it worked on first shot!
}
/***********************************************************/



t_stat eth_open (ETH_DEV* dev, char* name)
  {
	FILE *packetcount;
	char packetcountpath[255];
	PacketR=0;

   memset(Path,0x0,sizeof(Path));
   sprintf(Path,"%s",name);
   sprintf(Readpath,"%s\\%02X%02X%02X%02X%02X%02X",Path,dev->mac_address[0],dev->mac_address[1],dev->mac_address[2],dev->mac_address[3],dev->mac_address[4],dev->mac_address[5]);
   printf("\nPath:\t%s\nReadpath:\t%s\n",Path,Readpath);
   mkdir(Readpath);

   //Since we are new, we are going to reset the counter to 0.  We
   //wouldnt want the old packets anyways.  yes I knkow this will
   //liter the filesystem... clear those temp dirs!
   sprintf(packetcountpath,"%s\\packetcount",Readpath);
   packetcount=fopen(packetcountpath,"w");
   fprintf(packetcount,"0");
   fclose(packetcount);
   return SCPE_OK;
  }
 
t_stat eth_close (ETH_DEV* dev)
  {
        //rmdir(Readpath);
 return SCPE_NOFNC;
 }
 
 
/*************************************************************/
 
t_stat eth_write (ETH_DEV* dev, ETH_PACK* packet, ETH_PCALLBACK routine)
      {
      int status = 1;   /* default to failure */
      
  /* make sure device exists */
  if (!dev) return SCPE_UNATT;
 
  /* make sure packet exists */
  if (!packet) return SCPE_ARG;
 
  /* make sure packet is acceptable length */
  if ((packet->len >= ETH_MIN_PACKET) && (packet->len <= ETH_MAX_PACKET)) {
      char buffer[5000];
      char fname[255];
	  int	err=0;
      int   outz=0;
      int	FHpacketcount=0;	//filehandle for the packet file
      char  packetcountpath[255];
	  int	Packet=0; //the packet #
      
 
      //verify path exists first.. by making it.... 
      memset(packetcountpath,0x0,sizeof(packetcountpath));
      sprintf(packetcountpath,"%s\\%02X%02X%02X%02X%02X%02X",Path,packet->msg[0],packet->msg[1],packet->msg[2],packet->msg[3],packet->msg[4],packet->msg[5]);
      mkdir(packetcountpath);

	  sprintf(packetcountpath,"%s\\%02X%02X%02X%02X%02X%02X\\packetcount",Path,packet->msg[0],packet->msg[1],packet->msg[2],packet->msg[3],packet->msg[4],packet->msg[5]);
	  err=sopenreadcounter(&packetcountpath,&FHpacketcount);
	  
	  if(err==0) //The file didn't exist!  For now we'll just assume this works...
	  {
		FHpacketcount=sopen(packetcountpath,O_RDWR | O_BINARY | O_CREAT, SH_DENYRW, S_IREAD | S_IWRITE);
		Packet=0;
	  }
	  if(err==-1)//something bombed!
	  {
#ifdef DEBUG
		  printf("something bombed openening the packet counter");
#endif
		  exit(-1);
	  }
	  if(err==1)
	  {
		  char buffer[20];
		  memset(buffer,0x0,sizeof(buffer));
		  read(FHpacketcount,buffer,sizeof(buffer));
		  sscanf(buffer,"%d",&Packet);
		  lseek(FHpacketcount,0,0);
	  }
      
   memset(buffer,0x0,sizeof(buffer));
   memset(fname,0x0,sizeof(fname));

   sprintf(fname,"%s\\%02X%02X%02X%02X%02X%02X\\packet_%d.cap",Path,packet->msg[0],packet->msg[1],packet->msg[2],packet->msg[3],packet->msg[4],packet->msg[5],Packet);

   //printf("writing frame %s\n",fname);

   outz=sopen(fname,O_RDWR | O_BINARY | O_CREAT, SH_DENYRW, S_IREAD | S_IWRITE);
   eth_add_crc32(packet->msg);
   write(outz,packet->msg,packet->len);
   close(outz);
   status=0;
   Packet++;
   {
	   char buffer[20];
	   memset(buffer,0x0,sizeof(buffer));
	   sprintf(buffer,"%d",Packet);
#ifdef DEBUG
	   printf("Writing packetcount[%d] %s\n",Packet,packetcountpath);
#endif
	   write(FHpacketcount,buffer,sizeof(buffer));
	   close(FHpacketcount);
   }
    /* detect sending of decnet loopback packet */
    if ((status == 0) && DECNET_SELF_FRAME(dev->decnet_addr, packet->msg)) 
      dev->decnet_self_sent += dev->reflections;
 
  } /* if packet->len */
 
  /* call optional write callback function */
  if (routine)
    (routine)(status);
  return SCPE_OK;
}
 
/*************************************************************/
t_stat eth_read (ETH_DEV* dev, ETH_PACK* packet, ETH_PCALLBACK routine)
  {
  int status;
 
  /* make sure device exists */
  if (!dev) return SCPE_UNATT;
 
  /* make sure packet exists */
  if (!packet) return SCPE_ARG;
 
  /* set read packet */
  dev->read_packet = packet;
  packet->len = 0;
 
  /* set optional callback routine */
  dev->read_callback = routine;
 
  /* dispatch read request to either receive a filtered packet or timeout */
  do 
  {
	  char fname[255];
	  FILE *inz;
      FILE *packetcount;
      int j=0;

	  sprintf(fname,"%s\\packet_%d.cap",Readpath,PacketR); 
#ifdef DEBUG
      //printf("eth_read from %s\n",fname);
#endif

  inz=sopen(fname,O_RDWR | O_BINARY, SH_DENYRW);
 
 if(inz==-1)
 {
  return SCPE_OK;
 }
 else
 {
  unsigned char packetbuffer[2000];
  memset(packetbuffer,0x0,sizeof(packetbuffer));
  j=read(inz,packetbuffer,sizeof(packetbuffer));
  close(inz); 
  unlink(fname);
#ifdef DEBUG
  printf("read frame %s\n",fname);
#endif
  
  dev->read_packet->len=j;
  memcpy(dev->read_packet->msg,packetbuffer,j);
  eth_add_crc32(dev->read_packet);
  if (dev->read_callback)
   (dev->read_callback)(0);
  PacketR++;
 }
  
  return SCPE_OK;
 } while ((status) && (0 == packet->len));
}
 
 
 
t_stat eth_filter (ETH_DEV* dev, int addr_count, ETH_MAC* addresses,
                   ETH_BOOL all_multicast, ETH_BOOL promiscuous)
  {return SCPE_NOFNC;}
int eth_devices (int max, ETH_LIST* dev)
  {return 0;}

#endif
////////////////////////////////////////////////////////////////////////