summaryrefslogtreecommitdiff
path: root/gdb/m68k-stub.c
blob: 4ef4069bc3dfab4ad7b740826c0be597fd064da3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
/****************************************************************************

		THIS SOFTWARE IS NOT COPYRIGHTED  
   
   HP offers the following for use in the public domain.  HP makes no
   warranty with regard to the software or it's performance and the 
   user accepts the software "AS IS" with all faults.

   HP DISCLAIMS ANY WARRANTIES, EXPRESS OR IMPLIED, WITH REGARD
   TO THIS SOFTWARE INCLUDING BUT NOT LIMITED TO THE WARRANTIES
   OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

****************************************************************************/

/****************************************************************************
 *  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
 * 
 ****************************************************************************/

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

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

extern void putDebugChar();	/* write a single character      */
extern int getDebugChar();	/* read and return a single char */

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

/************************/
/* FORWARD DECLARATIONS */
/************************/
static void
initializeRemcomErrorFrame ();

/************************************************************************/
/* 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;

#ifdef 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

#ifdef 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 *************************/
/* 									   */

#ifdef __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 return_to_user();

asm("
.text
.globl _return_to_super
_return_to_super:
        movel   _registers+60,sp /* get new stack pointer */        
        movel   _lastFrame,a0   /* get last frame info  */              
        bra     return_to_any

.globl _return_to_user
_return_to_user:
        movel   _registers+60,a0 /* get usp */                          
        movel   a0,usp           /* set usp */				
        movel   _superStack,sp  /* get original stack pointer */        

return_to_any:
        movel   _lastFrame,a0   /* get last frame info  */              
        movel   a0@+,_lastFrame /* link in previous frame     */        
        addql   #8,a0           /* skip over pc, vector#*/              
        movew   a0@+,d0         /* get # of words in cpu frame */       
        addw    d0,a0           /* point to end of data        */       
        addw    d0,a0           /* point to end of data        */       
        movel   a0,a1                                                   
#                                                                       
# copy the stack frame                                                  
        subql   #1,d0                                                   
copyUserLoop:                                                               
        movew   a1@-,sp@-                                               
        dbf     d0,copyUserLoop                                             
");                                                                     
        RESTORE_FP_REGS()                                              
   asm("   moveml  _registers,d0-d7/a0-a6");			        
   asm("   rte");  /* pop and go! */                                    

#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("
.text
.globl __debug_level7
__debug_level7:
	movew   d0,sp@-");
#if defined (mc68020) || defined (mc68332)
asm("	movew   sp@(2),d0");
#else
asm("	movew   sp@(6),d0");
#endif
asm("	andiw   #0x700,d0
	cmpiw   #0x700,d0
	beq     _already7
        movew   sp@+,d0	
        bra     __catchException
_already7:
	movew   sp@+,d0");
#if !defined (mc68020) && !defined (mc68332)
asm("	lea     sp@(4),sp");     /* pull off 68000 return address */
#endif
asm("	rte");

extern void _catchException ();

#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(" 
.text
.globl __catchException
__catchException:");
DISABLE_INTERRUPTS();
asm("
        moveml  d0-d7/a0-a6,_registers /* save registers        */
	movel	_lastFrame,a0	/* last frame pointer */
");
SAVE_FP_REGS();        
asm("
	lea     _registers,a5   /* get address of registers     */
        movew   sp@,d1          /* get status register          */
        movew   d1,a5@(66)      /* save sr		 	*/	
	movel   sp@(2),a4       /* save pc in a4 for later use  */
        movel   a4,a5@(68)      /* save pc in _regisers[]      	*/

#
# figure out how many bytes in the stack frame
	movew   sp@(6),d0	/* get '020 exception format	*/
        movew   d0,d2           /* make a copy of format word   */
        andiw   #0xf000,d0      /* mask off format type         */
        rolw    #5,d0           /* rotate into the low byte *2  */
        lea     _exceptionSize,a1   
        addw    d0,a1           /* index into the table         */
	movew   a1@,d0          /* get number of words in frame */
        movew   d0,d3           /* save it                      */
        subw    d0,a0		/* adjust save pointer          */
        subw    d0,a0		/* adjust save pointer(bytes)   */
	movel   a0,a1           /* copy save pointer            */
	subql   #1,d0           /* predecrement loop counter    */
#
# copy the frame
saveFrameLoop:
	movew  	sp@+,a1@+
	dbf     d0,saveFrameLoop
#
# now that the stack has been clenaed,
# save the a7 in use at time of exception
        movel   sp,_superStack  /* save supervisor sp           */
        andiw   #0x2000,d1      /* were we in supervisor mode ? */
        beq     userMode       
        movel   a7,a5@(60)      /* save a7                  */
        bra     a7saveDone
userMode:  
	movel   usp,a1    	
        movel   a1,a5@(60)      /* save user stack pointer	*/
a7saveDone:

#
# save size of frame
        movew   d3,a0@-

#
# compute exception number
	andl    #0xfff,d2   	/* mask off vector offset	*/
	lsrw    #2,d2   	/* divide by 4 to get vect num	*/
        movel   d2,a0@-         /* save it                      */
#
# save pc causing exception
        movel   a4,a0@-
#
# save old frame link and set the new value
	movel	_lastFrame,a1	/* last frame pointer */
	movel   a1,a0@-		/* save pointer to prev frame	*/
        movel   a0,_lastFrame

        movel   d2,sp@-		/* push exception num           */
	movel   _exceptionHook,a0  /* get address of handler */
        jbsr    a0@             /* and call it */
        clrl    sp@             /* replace exception num parm with frame ptr */
        jbsr     __returnFromException   /* jbsr, but never returns */
");
#else /* mc68000 */
/* This function is called when an exception occurs.  It translates the
 * return address found on the stack into an exception vector # which
 * is then handled by either handle_exception or a system handler.
 * _catchException provides a front end for both.  
 *
 * stack on entry:                       stack on exit:
 *   Program counter MSWord              exception # MSWord 
 *   Program counter LSWord              exception # MSWord
 *   Status Register                     
 *   Return Address  MSWord              
 *   Return Address  LSWord             
 */
asm("
.text
.globl __catchException
__catchException:");
DISABLE_INTERRUPTS();
asm("
        moveml d0-d7/a0-a6,_registers  /* save registers               */
	movel	_lastFrame,a0	/* last frame pointer */
");
SAVE_FP_REGS();        
asm("
        lea     _registers,a5   /* get address of registers     */
        movel   sp@+,d2         /* pop return address           */
	addl 	#1530,d2        /* convert return addr to 	*/
	divs 	#6,d2   	/*  exception number		*/
	extl    d2   

        moveql  #3,d3           /* assume a three word frame     */

        cmpiw   #3,d2           /* bus error or address error ? */
        bgt     normal          /* if >3 then normal error      */
        movel   sp@+,a0@-       /* copy error info to frame buff*/
        movel   sp@+,a0@-       /* these are never used         */
        moveql  #7,d3           /* this is a 7 word frame       */
     
normal:   
	movew   sp@+,d1         /* pop status register          */
        movel   sp@+,a4         /* pop program counter          */
        movew   d1,a5@(66)      /* save sr		 	*/	
        movel   a4,a5@(68)      /* save pc in _regisers[]      	*/
        movel   a4,a0@-         /* copy pc to frame buffer      */
	movew   d1,a0@-         /* copy sr to frame buffer      */

        movel   sp,_superStack  /* save supervisor sp          */

        andiw   #0x2000,d1      /* were we in supervisor mode ? */
        beq     userMode       
        movel   a7,a5@(60)      /* save a7                  */
        bra     saveDone             
userMode:
        movel   usp,a1    	/* save user stack pointer 	*/
        movel   a1,a5@(60)      /* save user stack pointer	*/
saveDone:

        movew   d3,a0@-         /* push frame size in words     */
        movel   d2,a0@-         /* push vector number           */
        movel   a4,a0@-         /* push exception pc            */

#
# save old frame link and set the new value
	movel	_lastFrame,a1	/* last frame pointer */
	movel   a1,a0@-		/* save pointer to prev frame	*/
        movel   a0,_lastFrame

        movel   d2,sp@-		/* push exception num           */
	movel   _exceptionHook,a0  /* get address of handler */
        jbsr    a0@             /* and call it */
        clrl    sp@             /* replace exception num parm with frame ptr */
        jbsr     __returnFromException   /* jbsr, but never returns */
");
#endif


/*
 * remcomHandler is a front end for handle_exception.  It moves the
 * stack pointer into an area reserved for debugger use in case the
 * breakpoint happened in supervisor mode.
 */
asm("_remcomHandler:");
asm("           addl    #4,sp");        /* pop off return address     */
asm("           movel   sp@+,d0");      /* get the exception number   */
asm("		movel   _stackPtr,sp"); /* move to remcom stack area  */
asm("		movel   d0,sp@-");	/* push exception onto stack  */
asm("		jbsr    _handle_exception");    /* this never returns */
asm("           rts");                  /* return */

void
_returnFromException (Frame * frame)
{
  /* if no passed in frame, use the last one */
  if (!frame)
    {
      frame = lastFrame;
      frame->frameSize = 4;
      frame->format = 0;
      frame->fsaveHeader = -1;	/* restore regs, but we dont have fsave info */
    }

#if !defined (mc68020) && !defined (mc68332)
  /* a 68000 cannot use the internal info pushed onto a bus error
   * or address error frame when doing an RTE so don't put this info
   * onto the stack or the stack will creep every time this happens.
   */
  frame->frameSize = 3;
#endif

  /* throw away any frames in the list after this frame */
  lastFrame = frame;

  frame->sr = registers[(int) PS];
  frame->pc = registers[(int) PC];

  if (registers[(int) PS] & 0x2000)
    {
      /* return to supervisor mode... */
      return_to_super ();
    }
  else
    {				/* return to user mode */
      return_to_user ();
    }
}

int
hex (ch)
     char ch;
{
  if ((ch >= 'a') && (ch <= 'f'))
    return (ch - 'a' + 10);
  if ((ch >= '0') && (ch <= '9'))
    return (ch - '0');
  if ((ch >= 'A') && (ch <= 'F'))
    return (ch - 'A' + 10);
  return (-1);
}

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

/* scan for the sequence $<data>#<checksum>     */

unsigned char *
getpacket (void)
{
  unsigned char *buffer = &remcomInBuffer[0];
  unsigned char checksum;
  unsigned char xmitcsum;
  int count;
  char ch;

  while (1)
    {
      /* wait around for the start character, ignore all other characters */
      while ((ch = getDebugChar ()) != '$')
	;

    retry:
      checksum = 0;
      xmitcsum = -1;
      count = 0;

      /* now, read until a # or end of buffer is found */
      while (count < BUFMAX - 1)
	{
	  ch = getDebugChar ();
	  if (ch == '$')
	    goto retry;
	  if (ch == '#')
	    break;
	  checksum = checksum + ch;
	  buffer[count] = ch;
	  count = count + 1;
	}
      buffer[count] = 0;

      if (ch == '#')
	{
	  ch = getDebugChar ();
	  xmitcsum = hex (ch) << 4;
	  ch = getDebugChar ();
	  xmitcsum += hex (ch);

	  if (checksum != xmitcsum)
	    {
	      if (remote_debug)
		{
		  fprintf (stderr,
			   "bad checksum.  My count = 0x%x, sent=0x%x. buf=%s\n",
			   checksum, xmitcsum, buffer);
		}
	      putDebugChar ('-');	/* failed checksum */
	    }
	  else
	    {
	      putDebugChar ('+');	/* successful transfer */

	      /* if a sequence char is present, reply the sequence ID */
	      if (buffer[2] == ':')
		{
		  putDebugChar (buffer[0]);
		  putDebugChar (buffer[1]);

		  return &buffer[3];
		}

	      return &buffer[0];
	    }
	}
    }
}

/* send the packet in buffer. */

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])
	{
	  putDebugChar (ch);
	  checksum += ch;
	  count += 1;
	}

      putDebugChar ('#');
      putDebugChar (hexchars[checksum >> 4]);
      putDebugChar (hexchars[checksum % 16]);

    }
  while (getDebugChar () != '+');

}

void
debug_error (format, parm)
     char *format;
     char *parm;
{
  if (remote_debug)
    fprintf (stderr, format, parm);
}

/* 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);
}

/* a bus error has occurred, perform a longjmp
   to return execution and allow handling of the error */

void
handle_buserror ()
{
  longjmp (remcomEnv, 1);
}

/* 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, stepping;
  int addr, length;
  char *ptr;
  int newPC;
  Frame *frame;

  if (remote_debug)
    printf ("vector=%d, sr=0x%x, pc=0x%x\n",
	    exceptionVector, registers[PS], registers[PC]);

  /* 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);

  stepping = 0;

  while (1 == 1)
    {
      remcomOutBuffer[0] = 0;
      ptr = getpacket ();
      switch (*ptr++)
	{
	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 (ptr, (char *) registers, NUMREGBYTES);
	  strcpy (remcomOutBuffer, "OK");
	  break;

	  /* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
	case 'm':
	  if (setjmp (remcomEnv) == 0)
	    {
	      exceptionHandler (2, handle_buserror);

	      /* TRY TO READ %x,%x.  IF SUCCEED, SET PTR = 0 */
	      if (hexToInt (&ptr, &addr))
		if (*(ptr++) == ',')
		  if (hexToInt (&ptr, &length))
		    {
		      ptr = 0;
		      mem2hex ((char *) addr, remcomOutBuffer, length);
		    }

	      if (ptr)
		{
		  strcpy (remcomOutBuffer, "E01");
		}
	    }
	  else
	    {
	      exceptionHandler (2, _catchException);
	      strcpy (remcomOutBuffer, "E03");
	      debug_error ("bus error");
	    }

	  /* restore handler for bus error */
	  exceptionHandler (2, _catchException);
	  break;

	  /* MAA..AA,LLLL: Write LLLL bytes at address AA.AA return OK */
	case 'M':
	  if (setjmp (remcomEnv) == 0)
	    {
	      exceptionHandler (2, handle_buserror);

	      /* TRY TO READ '%x,%x:'.  IF SUCCEED, SET PTR = 0 */
	      if (hexToInt (&ptr, &addr))
		if (*(ptr++) == ',')
		  if (hexToInt (&ptr, &length))
		    if (*(ptr++) == ':')
		      {
			hex2mem (ptr, (char *) addr, length);
			ptr = 0;
			strcpy (remcomOutBuffer, "OK");
		      }
	      if (ptr)
		{
		  strcpy (remcomOutBuffer, "E02");
		}
	    }
	  else
	    {
	      exceptionHandler (2, _catchException);
	      strcpy (remcomOutBuffer, "E03");
	      debug_error ("bus error");
	    }

	  /* restore handler for bus error */
	  exceptionHandler (2, _catchException);
	  break;

	  /* cAA..AA    Continue at address AA..AA(optional) */
	  /* sAA..AA   Step one instruction from AA..AA(optional) */
	case 's':
	  stepping = 1;
	case 'c':
	  /* try to read optional parameter, pc unchanged if no parm */
	  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 (stepping)
	    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().
	   */
	  if (remote_debug)
	    printf ("new pc = 0x%x\n", newPC);
	  frame = lastFrame;
	  while (frame)
	    {
	      if (remote_debug)
		printf ("frame at 0x%x has pc=0x%x, except#=%d\n",
			frame, frame->exceptionPC, frame->exceptionVector);
	      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)
		    {
		      if (remote_debug)
			printf ("frame at 0x%x has pc=0x%x, except#=%d\n",
				frame, frame->exceptionPC,
				frame->exceptionVector);
		      /* 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 (void)
{
  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++)
    exceptionHandler (exception, _catchException);

  /* level 7 interrupt              */
  exceptionHandler (31, _debug_level7);

  /* breakpoint exception (trap #1) */
  exceptionHandler (33, _catchException);

  /* 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?  */
  exceptionHandler (40, _catchException);

  /* 48 to 54 are floating point coprocessor errors */
  for (exception = 48; exception <= 54; exception++)
    exceptionHandler (exception, _catchException);

  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 ();
}