m68k-stub.c

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

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/****************************************************************************
 *  Header: remcom.c,v 1.34 91/03/09 12:29:49 glenne Exp $                   
 *
 *  Module name: remcom.c $  
 *  Revision: 1.34 $
 *  Date: 91/03/09 12:29:49 $
 *  Contributor:     Lake Stevens Instrument Division$
 *  
 *  Description:     low level support for gdb debugger. $
 *
 *  Considerations:  only works on target hardware $
 *
 *  Written by:      Glenn Engel $
 *  ModuleState:     Experimental $ 
 *
 *  NOTES:           See Below $
 * 
 *  To enable debugger support, two things need to happen.  One, a
 *  call to set_debug_traps() is necessary in order to allow any breakpoints
 *  or error conditions to be properly intercepted and reported to gdb.
 *  Two, a breakpoint needs to be generated to begin communication.  This
 *  is most easily accomplished by a call to breakpoint().  Breakpoint()
 *  simulates a breakpoint by executing a trap #1.  The breakpoint instruction
 *  is hardwired to trap #1 because not to do so is a compatibility problem--
 *  there either should be a standard breakpoint instruction, or the protocol
 *  should be extended to provide some means to communicate which breakpoint
 *  instruction is in use (or have the stub insert the breakpoint).
 *  
 *  Some explanation is probably necessary to explain how exceptions are
 *  handled.  When an exception is encountered the 68000 pushes the current
 *  program counter and status register onto the supervisor stack and then
 *  transfers execution to a location specified in it's vector table.
 *  The handlers for the exception vectors are hardwired to jmp to an address
 *  given by the relation:  (exception - 256) * 6.  These are decending 
 *  addresses starting from -6, -12, -18, ...  By allowing 6 bytes for
 *  each entry, a jsr, jmp, bsr, ... can be used to enter the exception 
 *  handler.  Using a jsr to handle an exception has an added benefit of
 *  allowing a single handler to service several exceptions and use the
 *  return address as the key differentiation.  The vector number can be
 *  computed from the return address by [ exception = (addr + 1530) / 6 ].
 *  The sole purpose of the routine _catchException is to compute the
 *  exception number and push it on the stack in place of the return address.
 *  The external function exceptionHandler() is
 *  used to attach a specific handler to a specific m68k exception.
 *  For 68020 machines, the ability to have a return address around just
 *  so the vector can be determined is not necessary because the '020 pushes an
 *  extra word onto the stack containing the vector offset
 * 
 *  Because gdb will sometimes write to the stack area to execute function
 *  calls, this program cannot rely on using the supervisor stack so it
 *  uses it's own stack area reserved in the int array remcomStack.  
 * 
 *************
 *
 *    The following gdb commands are supported:
 * 
 * command          function                               Return value
 * 
 *    g             return the value of the CPU registers  hex data or ENN
 *    G             set the value of the CPU registers     OK or ENN
 * 
 *    mAA..AA,LLLL  Read LLLL bytes at address AA..AA      hex data or ENN
 *    MAA..AA,LLLL: Write LLLL bytes at address AA.AA      OK or ENN
 * 
 *    c             Resume at current address              SNN   ( signal NN)
 *    cAA..AA       Continue at address AA..AA             SNN
 * 
 *    s             Step one instruction                   SNN
 *    sAA..AA       Step one instruction from AA..AA       SNN
 * 
 *    k             kill
 *
 *    ?             What was the last sigval ?             SNN   (signal NN)
 * 
 * All commands and responses are sent with a packet which includes a 
 * checksum.  A packet consists of 
 * 
 * $<packet info>#<checksum>.
 * 
 * where
 * <packet info> :: <characters representing the command or response>
 * <checksum>    :: < two hex digits computed as modulo 256 sum of <packetinfo>>
 * 
 * When a packet is received, it is first acknowledged with either '+' or '-'.
 * '+' indicates a successful transfer.  '-' indicates a failed transfer.
 * 
 * Example:
 * 
 * Host:                  Reply:
 * $m0,10#2a               +$00010203040506070809101112131415#42
 * 
 *  $Id: m68k-stub.c,v 1.5 2002/11/01 23:05:26 joel Exp $
 *
 ****************************************************************************/

#include <stdio.h>
#include <string.h>
#include <setjmp.h>

#include <bsp.h>
#include <debugport.h>

/************************************************************************
 *
 * external low-level support routines 
 */
typedef void (*ExceptionHook)(int);   /* pointer to function with int parm */
typedef void (*Function)(void);       /* pointer to a function */

/* assign an exception handler */
Function exceptionHandler(int vector,  Function handler);
extern ExceptionHook exceptionHook;  /* hook variable for errors/exceptions */

int putDebugChar(char ch);
char getDebugChar(void);

/************************/
/* FORWARD DECLARATIONS */
/************************/
static int hex(char ch);
static void getpacket(char *buffer);
static void putpacket(char *buffer);
static char* mem2hex(char *mem, char *buf, int count);
static char* hex2mem(char *buf, char *mem, int count);
static void handle_buserror(void);
static int computeSignal(int exceptionVector);
static int hexToInt(char **ptr, int *intValue);
       void handle_exception(int exceptionVector);
static void initializeRemcomErrorFrame(void);

void set_debug_traps(void);
void breakpoint(void);

/************************************************************************/
/* BUFMAX defines the maximum number of characters in inbound/outbound buffers*/
/* at least NUMREGBYTES*2 are needed for register packets */
#define BUFMAX 400

static char initialized;  /* boolean flag. != 0 means we've been initialized */

int remote_debug;
/*  debug >  0 prints ill-formed commands in valid packets & checksum errors */ 

static const char hexchars[]="0123456789abcdef";

/* there are 180 bytes of registers on a 68020 w/68881      */
/* many of the fpa registers are 12 byte (96 bit) registers */
#define NUMREGBYTES 180
enum regnames {D0,D1,D2,D3,D4,D5,D6,D7, 
               A0,A1,A2,A3,A4,A5,A6,A7, 
               PS,PC,
               FP0,FP1,FP2,FP3,FP4,FP5,FP6,FP7,
               FPCONTROL,FPSTATUS,FPIADDR
              };


/* We keep a whole frame cache here.  "Why?", I hear you cry, "doesn't
   GDB handle that sort of thing?"  Well, yes, I believe the only
   reason for this cache is to save and restore floating point state
   (fsave/frestore).  A cleaner way to do this would be to make the
 fsave data part of the registers which GDB deals with like any
   other registers.  This should not be a performance problem if the
   ability to read individual registers is added to the protocol.  */

typedef struct FrameStruct
{
    struct FrameStruct  *previous;
    int       exceptionPC;      /* pc value when this frame created */
    int       exceptionVector;  /* cpu vector causing exception     */
    short     frameSize;        /* size of cpu frame in words       */
    short     sr;               /* for 68000, this not always sr    */
    int       pc;
    short     format;
    int       fsaveHeader;
    int       morejunk[0];        /* exception frame, fp save... */
} Frame;

#define FRAMESIZE 500
int gdbFrameStack[FRAMESIZE];
static Frame *lastFrame;

/*
 * these should not be static cuz they can be used outside this module
 */
int registers[NUMREGBYTES/4];
int superStack;

#define STACKSIZE 10000
int remcomStack[STACKSIZE/sizeof(int)];
static int* stackPtr = &remcomStack[STACKSIZE/sizeof(int) - 1];

/*
 * In many cases, the system will want to continue exception processing
 * when a continue command is given.  
 * oldExceptionHook is a function to invoke in this case.
 */

static ExceptionHook oldExceptionHook;

#if defined(__mc68020__)
/* the size of the exception stack on the 68020 varies with the type of
 * exception.  The following table is the number of WORDS used
 * for each exception format.
 */
const short exceptionSize[] = { 4,4,6,4,4,4,4,4,29,10,16,46,12,4,4,4 };
#endif

#if defined(__mc68332__)
static const short exceptionSize[] = { 4,4,6,4,4,4,4,4,4,4,4,4,16,4,4,4 };
#endif

/************* jump buffer used for setjmp/longjmp **************************/
jmp_buf remcomEnv;

/***************************  ASSEMBLY CODE MACROS *************************/
/* 									   */

#if defined(__HAVE_68881__)

/* do an fsave, then remember the address to begin a restore from */
#define SAVE_FP_REGS() \
       asm(" fsave   %a0@-");	\
       asm(" fmovemx %fp0-%fp7,registers+72");  \
       asm(" fmoveml %fpcr/%fpsr/%fpi,registers+168");

#define RESTORE_FP_REGS() \
asm("                                                 \n\
    fmoveml  registers+168,%fpcr/%fpsr/%fpi           \n\
    fmovemx  registers+72,%fp0-%fp7                   \n\
    cmpl     #-1,%a0@     |  skip frestore flag set ? \n\
    beq      skip_frestore                            \n\
    frestore %a0@+                                    \n\
skip_frestore:                                        \n\
");

#else

#define SAVE_FP_REGS()
#define RESTORE_FP_REGS()

#endif /* __HAVE_68881__ */

void return_to_super(void);
void return_to_user(void);

asm("\n\
       .text\n\
\n\
       .globl return_to_super\n\
       .align 4\n\
return_to_super:\n\
        movel   registers+60,%sp     /* get new stack pointer */        \n\
        movel   lastFrame,%a0        /* get last frame info  */         \n\
        bra     return_to_any\n\
\n\
        .globl return_to_user\n\
        .align 4\n\
\n\
return_to_user:\n\
        movel   registers+60,%a0     /* get usp */                      \n\
        movel   %a0,%usp             /* set usp */				\n\
        movel   superStack,%sp       /* get original stack pointer */        \n\
\n\
return_to_any:\n\
        movel   lastFrame,%a0        /* get last frame info  */              \n\
        movel   %a0@+,lastFrame      /* link in previous frame     */        \n\
        addql   #8,%a0               /* skip over pc, vector#*/              \n\
        movew   %a0@+,%d0            /* get # of words in cpu frame */       \n\
        addw    %d0,%a0              /* point to end of data        */       \n\
        addw    %d0,%a0              /* point to end of data        */       \n\
        movel   %a0,%a1                                                   \n\
#                                                                       \n\
# copy the stack frame                                                  \n\
        subql   #1,%d0\n\
\n\
copyUserLoop:                                                               \n\
        movew   %a1@-,%sp@-                                               \n\
        dbf     %d0,copyUserLoop                                             \n\
");
        RESTORE_FP_REGS()
asm("\n\
        moveml  registers,%d0-%d7/%a0-%a6\n\
        rte                          /* pop and go! */\n\
");

#define DISABLE_INTERRUPTS() asm("   oriw   #0x0700,%sr");
#define BREAKPOINT()         asm("   trap   #1");

/* this function is called immediately when a level 7 interrupt occurs */
/* if the previous interrupt level was 7 then we're already servicing  */
/* this interrupt and an rte is in order to return to the debugger.    */
/* For the 68000, the offset for sr is 6 due to the jsr return address */
asm("\n\
        .text\n\
        .globl _debug_level7\n\
        .align 4\n\
\n\
_debug_level7:\n\
        movew   %d0,%sp@-\n\
");

#if defined(__mc68020__) || defined(__mc68332__)
asm("\n\
        movew   %sp@(2),%d0\n\
");
#else
asm("\n\
        movew   %sp@(6),%d0\n\
");
#endif
asm("\n\
        andiw   #0x700,%d0\n\
    	  cmpiw   #0x700,%d0\n\
    	  beq     _already7\n\
        movew   %sp@+,%d0	\n\
        bra     _catchException\n\
_already7:\n\
	      movew   %sp@+,%d0\n\
");
#if defined (__mc68000__) && !defined(__mc68020__)
asm("\n\
        lea     %sp@(4),%sp");       /* pull off 68000 return address */
#endif
asm("\n\
        rte\n\
");

extern void _catchException(void);

#if defined(__mc68020__) || defined(__mc68332__)
/* This function is called when a 68020 exception occurs.  It saves
 * all the cpu and fpcp regs in the _registers array, creates a frame on a
 * linked list of frames which has the cpu and fpcp stack frames needed
 * to properly restore the context of these processors, and invokes
 * an exception handler (remcom_handler).
 *
 * stack on entry:                       stack on exit:
 *   N bytes of junk                     exception # MSWord
 *   Exception Format Word               exception # MSWord
 *   Program counter LSWord              
 *   Program counter MSWord             
 *   Status Register                    
 *                                       
 *                                       
 */
asm(" \n\
        .text\n\
\n\
        .globl _catchException\n\