m68k-stub.c

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

/* send the packet in buffer.  The host get's one chance to read it.  
   This routine does not wait for a positive acknowledge.  */


void putpacket(buffer)
char * buffer;
{
  unsigned char checksum;
  int  count;
  char ch;
  
  /*  $<packet info>#<checksum>. */
  do {
  putDebugChar('$');
  checksum = 0;
  count    = 0;
  
  while ((ch=buffer[count])) {
    if (! putDebugChar(ch)) return;
    checksum += ch;
    count += 1;
  }
  
  putDebugChar('#');
  putDebugChar(hexchars[checksum >> 4]);
  putDebugChar(hexchars[checksum % 16]);

  } while (1 == 0);  /* (getDebugChar() != '+'); */
  
}

char  remcomInBuffer[BUFMAX];
char  remcomOutBuffer[BUFMAX];
static short error;


void debug_error(format, parm)
char * format;
char * parm;
{
  return;
}

/* convert the memory pointed to by mem into hex, placing result in buf */
/* return a pointer to the last char put in buf (null) */
char* mem2hex(mem, buf, count)
char* mem;
char* buf;
int   count;
{
      int i;
      unsigned char ch;
      for (i=0;i<count;i++) {
          ch = *mem++;
          *buf++ = hexchars[ch >> 4];
          *buf++ = hexchars[ch % 16];
      }
      *buf = 0; 
      return(buf);
}

/* convert the hex array pointed to by buf into binary to be placed in mem */
/* return a pointer to the character AFTER the last byte written */
char* hex2mem(buf, mem, count)
char* buf;
char* mem;
int   count;
{
      int i;
      unsigned char ch;
      for (i=0;i<count;i++) {
          ch = hex(*buf++) << 4;
          ch = ch + hex(*buf++);
          *mem++ = ch;
      }
      return(mem);
}

/* this function takes the 68000 exception number and attempts to 
   translate this number into a unix compatible signal value */
int computeSignal( exceptionVector )
int exceptionVector;
{
  int sigval;
  switch (exceptionVector) {
    case 2 : sigval = 10; break; /* bus error           */
    case 3 : sigval = 10; break; /* address error       */
    case 4 : sigval = 4;  break; /* illegal instruction */
    case 5 : sigval = 8;  break; /* zero divide         */
    case 6 : sigval = 8; break; /* chk instruction     */
    case 7 : sigval = 8; break; /* trapv instruction   */
    case 8 : sigval = 11; break; /* privilege violation */
    case 9 : sigval = 5;  break; /* trace trap          */
    case 10: sigval = 4;  break; /* line 1010 emulator  */
    case 11: sigval = 4;  break; /* line 1111 emulator  */

      /* Coprocessor protocol violation.  Using a standard MMU or FPU
	 this cannot be triggered by software.  Call it a SIGBUS.  */
    case 13: sigval = 10;  break;

    case 31: sigval = 2;  break; /* interrupt           */
    case 33: sigval = 5;  break; /* breakpoint          */

      /* This is a trap #8 instruction.  Apparently it is someone's software
	 convention for some sort of SIGFPE condition.  Whose?  How many
	 people are being screwed by having this code the way it is?
	 Is there a clean solution?  */
    case 40: sigval = 8;  break; /* floating point err  */

    case 48: sigval = 8;  break; /* floating point err  */
    case 49: sigval = 8;  break; /* floating point err  */
    case 50: sigval = 8;  break; /* zero divide         */
    case 51: sigval = 8;  break; /* underflow           */
    case 52: sigval = 8;  break; /* operand error       */
    case 53: sigval = 8;  break; /* overflow            */
    case 54: sigval = 8;  break; /* NAN                 */
    default: 
      sigval = 7;         /* "software generated"*/
  }
  return (sigval);
}

/**********************************************/
/* WHILE WE FIND NICE HEX CHARS, BUILD AN INT */
/* RETURN NUMBER OF CHARS PROCESSED           */
/**********************************************/
int hexToInt(char **ptr, int *intValue)
{
    int numChars = 0;
    int hexValue;
    
    *intValue = 0;

    while (**ptr)
    {
        hexValue = hex(**ptr);
        if (hexValue >=0)
        {
            *intValue = (*intValue <<4) | hexValue;
            numChars ++;
        }
        else
            break;
        
        (*ptr)++;
    }

    return (numChars);
}

/*
 * This function does all command procesing for interfacing to gdb.
 */
void handle_exception(int exceptionVector)
{
  int    sigval;
  int    addr, length;
  char * ptr;
  int    newPC;
  Frame  *frame;
  
  /* reply to host that an exception has occurred */
  sigval = computeSignal( exceptionVector );
  remcomOutBuffer[0] = 'S';
  remcomOutBuffer[1] =  hexchars[sigval >> 4];
  remcomOutBuffer[2] =  hexchars[sigval % 16];
  remcomOutBuffer[3] = 0;

  putpacket(remcomOutBuffer); 

  while (1==1) { 
    error = 0;
    remcomOutBuffer[0] = 0;
    getpacket(remcomInBuffer);
    switch (remcomInBuffer[0]) {
      case '?' :   remcomOutBuffer[0] = 'S';
                   remcomOutBuffer[1] =  hexchars[sigval >> 4];
                   remcomOutBuffer[2] =  hexchars[sigval % 16];
                   remcomOutBuffer[3] = 0;
                 break; 
      case 'd' : remote_debug = !(remote_debug);  /* toggle debug flag */
                 break; 
      case 'g' : /* return the value of the CPU registers */
                mem2hex((char*) registers, remcomOutBuffer, NUMREGBYTES);
                break;
      case 'G' : /* set the value of the CPU registers - return OK */
                hex2mem(&remcomInBuffer[1], (char*) registers, NUMREGBYTES);
                db_strcpy(remcomOutBuffer,"OK");
                break;
      
      /* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
      case 'm' : 
	/* TRY TO READ %x,%x.  IF SUCCEED, SET PTR = 0 */
	ptr = &remcomInBuffer[1];
	if (hexToInt(&ptr,&addr))
	  if (*(ptr++) == ',')
	    if (hexToInt(&ptr,&length)) 
	      {
		ptr = 0;
		mem2hex((char*) addr, remcomOutBuffer, length);
	      }
	
	if (ptr)
	  {
	    db_strcpy(remcomOutBuffer,"E01");
	    debug_error("malformed read memory command: %s",remcomInBuffer);
	  }     
        break;
      
      /* MAA..AA,LLLL: Write LLLL bytes at address AA.AA return OK */
      case 'M' : 
	/* TRY TO READ '%x,%x:'.  IF SUCCEED, SET PTR = 0 */
	ptr = &remcomInBuffer[1];
	if (hexToInt(&ptr,&addr))
	  if (*(ptr++) == ',')
	    if (hexToInt(&ptr,&length))
	      if (*(ptr++) == ':')
		{
		  hex2mem(ptr, (char*) addr, length);
		  ptr = 0;
		  db_strcpy(remcomOutBuffer,"OK");
		}
	if (ptr)
	  {
	    db_strcpy(remcomOutBuffer,"E02");
	    debug_error("malformed write memory command: %s",remcomInBuffer);
	  }     
	break;
     
     /* cAA..AA    Continue at address AA..AA(optional) */
     /* sAA..AA   Step one instruction from AA..AA(optional) */
     case 'c' : 
     case 's' : 
          /* try to read optional parameter, pc unchanged if no parm */
         ptr = &remcomInBuffer[1];
         if (hexToInt(&ptr,&addr))
             registers[ PC ] = addr;
             
          newPC = registers[ PC];
          
          /* clear the trace bit */
          registers[ PS ] &= 0x7fff;
          
          /* set the trace bit if we're stepping */
          if (remcomInBuffer[0] == 's') registers[ PS ] |= 0x8000;
          
          /*
           * look for newPC in the linked list of exception frames.
           * if it is found, use the old frame it.  otherwise,
           * fake up a dummy frame in returnFromException().
           */
          frame = lastFrame;
          while (frame)
          {
              if (frame->exceptionPC == newPC) break;  /* bingo! a match */
              /*
               * for a breakpoint instruction, the saved pc may
               * be off by two due to re-executing the instruction
               * replaced by the trap instruction.  Check for this.
               */
              if ((frame->exceptionVector == 33) &&
                  (frame->exceptionPC == (newPC+2))) break;
              if (frame == frame->previous)
	      {
	          frame = 0; /* no match found */ 
	          break; 
	      }
	      frame = frame->previous;
          }
          
          /*
           * If we found a match for the PC AND we are not returning
           * as a result of a breakpoint (33),
           * trace exception (9), nmi (31), jmp to
           * the old exception handler as if this code never ran.
           */
          if (frame) 
          {
              if ((frame->exceptionVector != 9)  && 
                  (frame->exceptionVector != 31) && 
                  (frame->exceptionVector != 33))
              { 
                  /*
                   * invoke the previous handler.
                   */
                  if (oldExceptionHook)
                      (*oldExceptionHook) (frame->exceptionVector);
                  newPC = registers[ PC ];    /* pc may have changed  */
                  if (newPC != frame->exceptionPC)
                  {
                      /* re-use the last frame, we're skipping it (longjump?)*/
		      frame = (Frame *) 0;
	              _returnFromException( frame );  /* this is a jump */
                  }
              }
          }         

    	  /* if we couldn't find a frame, create one */
          if (frame == 0)
	  {
    	      frame = lastFrame -1 ;
	      
	      /* by using a bunch of print commands with breakpoints,
    	         it's possible for the frame stack to creep down.  If it creeps
		 too far, give up and reset it to the top.  Normal use should
    	         not see this happen.
    	      */
	      if ((unsigned int) (frame-2) < (unsigned int) &gdbFrameStack)
    	      {
    	         initializeRemcomErrorFrame();
    	         frame = lastFrame; 
	      }
    	      frame->previous = lastFrame;
              lastFrame = frame;
              frame = 0;  /* null so _return... will properly initialize it */ 
	  }    
	  
	  _returnFromException( frame ); /* this is a jump */

          break;
          
      /* kill the program */
      case 'k' :  /* do nothing */
                break;
      } /* switch */ 
    
    /* reply to the request */
    putpacket(remcomOutBuffer); 
    }
}


void
initializeRemcomErrorFrame()
{
    lastFrame = ((Frame *) &gdbFrameStack[FRAMESIZE-1]) - 1;
    lastFrame->previous = lastFrame;
}

/* this function is used to set up exception handlers for tracing and 
   breakpoints */
void set_debug_traps()
{
  extern void _debug_level7();
  extern void remcomHandler();
  int exception;

  initializeRemcomErrorFrame();
  stackPtr  = &remcomStack[STACKSIZE/sizeof(int) - 1];

  for (exception = 2; exception <= 23; exception++)
      set_vector(_catchException,exception,0);   

  /* level 7 interrupt              */
  set_vector(_debug_level7,31,0);    
  
  /* breakpoint exception (trap #1) */
  set_vector(_catchException,33,0);
  
  /* This is a trap #8 instruction.  Apparently it is someone's software
     convention for some sort of SIGFPE condition.  Whose?  How many
     people are being screwed by having this code the way it is?
     Is there a clean solution?  */
  set_vector(_catchException,40,0);
  
  /* 48 to 54 are floating point coprocessor errors */
  for (exception = 48; exception <= 54; exception++)
      set_vector(_catchException,exception,0);   

  if (oldExceptionHook != remcomHandler)
  {
      oldExceptionHook = exceptionHook;
      exceptionHook    = remcomHandler;
  }
  
  initialized = 1;

}

/* This function will generate a breakpoint exception.  It is used at the
   beginning of a program to sync up with a debugger and can be used
   otherwise as a quick means to stop program execution and "break" into
   the debugger. */
   
void breakpoint()
{
  if (initialized) BREAKPOINT();
}