sdcc/device/lib/pic16/startup/crt0.c

   1 /*-------------------------------------------------------------------------
   2    crt0.c - SDCC pic16 port runtime start code
   3
   4    Copyright (C) 2004, Vangelis Rokas <vrokas at otenet.gr>
   5
   6    This library is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by the
   8    Free Software Foundation; either version 2, or (at your option) any
   9    later version.
  10
  11    This library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this library; see the file COPYING. If not, write to the
  18    Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  19    MA 02110-1301, USA.
  20
  21    As a special exception, if you link this library with other files,
  22    some of which are compiled with SDCC, to produce an executable,
  23    this library does not by itself cause the resulting executable to
  24    be covered by the GNU General Public License. This exception does
  25    not however invalidate any other reasons why the executable file
  26    might be covered by the GNU General Public License.
  27 -------------------------------------------------------------------------*/
  28
  29 /*
  30  * based on Microchip MPLAB-C18 startup files
  31  */
  32
  33 extern int stack_end;
  34 extern int TBLPTRU;
  35
  36 /* external reference to the user's main routine */
  37 extern void main (void);
  38
  39 void _entry (void) __naked __interrupt (0);
  40 void _startup (void) __naked;
  41
  42 /* Access bank selector. */
  43 #define a 0
  44
  45
  46 /*
  47  * entry function, placed at interrupt vector 0 (RESET)
  48  */
  49 void
  50 _entry (void) __naked __interrupt (0)
  51 {
  52   __asm
  53     goto    __startup
  54   __endasm;
  55 }
  56
  57 void
  58 _startup (void) __naked
  59 {
  60   __asm
  61     ; Initialize the stack pointer
  62     lfsr    1, _stack_end
  63     lfsr    2, _stack_end
  64
  65     ; 1st silicon does not do this on POR
  66     clrf    _TBLPTRU, a
  67
  68     ; Initialize the flash memory access configuration.
  69     ; This is harmless for non-flash devices, so we do it on all parts.
  70     bsf     0xa6, 7, a      ; EECON1.EEPGD = 1, TBLPTR accesses program memory
  71     bcf     0xa6, 6, a      ; EECON1.CFGS  = 0, TBLPTR accesses program memory
  72   __endasm;
  73
  74   /* Call the main routine. */
  75   main ();
  76
  77   __asm
  78 lockup:
  79     ; Returning from main will lock up.
  80     bra     lockup
  81   __endasm;
  82 }