src/arch/i386/firmware/pcbios/gateA20.c

   1 #include "realmode.h"
   2 #include "timer.h"
   3 #include "latch.h"
   4 #include "bios.h"
   5
   6 #define K_RDWR          0x60            /* keyboard data & cmds (read/write) */
   7 #define K_STATUS        0x64            /* keyboard status */
   8 #define K_CMD           0x64            /* keybd ctlr command (write-only) */
   9
  10 #define K_OBUF_FUL      0x01            /* output buffer full */
  11 #define K_IBUF_FUL      0x02            /* input buffer full */
  12
  13 #define KC_CMD_WIN      0xd0            /* read  output port */
  14 #define KC_CMD_WOUT     0xd1            /* write output port */
  15 #define KB_SET_A20      0xdf            /* enable A20,
  16                                            enable output buffer full interrupt
  17                                            enable data line
  18                                            disable clock line */
  19 #define KB_UNSET_A20    0xdd            /* enable A20,
  20                                            enable output buffer full interrupt
  21                                            enable data line
  22                                            disable clock line */
  23
  24 enum { Disable_A20 = 0x2400, Enable_A20 = 0x2401, Query_A20_Status = 0x2402,
  25         Query_A20_Support = 0x2403 };
  26
  27 #define CF ( 1 << 0 )
  28
  29 #ifndef IBM_L40
  30 static void empty_8042 ( void )
  31 {
  32         unsigned long time;
  33         char st;
  34
  35         time = currticks() + TICKS_PER_SEC;     /* max wait of 1 second */
  36         while ((((st = inb(K_CMD)) & K_OBUF_FUL) ||
  37                (st & K_IBUF_FUL)) &&
  38                currticks() < time)
  39                 inb(K_RDWR);
  40 }
  41 #endif  /* IBM_L40 */
  42
  43 /*
  44  * Gate A20 for high memory
  45  *
  46  * Note that this function gets called as part of the return path from
  47  * librm's real_call, which is used to make the int15 call if librm is
  48  * being used.  To avoid an infinite recursion, we make gateA20_set
  49  * return immediately if it is already part of the call stack.
  50  */
  51 void gateA20_set ( void ) {
  52         static char reentry_guard = 0;
  53         unsigned int discard_a;
  54         unsigned int flags;
  55
  56         if ( reentry_guard )
  57                 return;
  58         reentry_guard = 1;
  59
  60         __asm__ __volatile__ ( REAL_CODE ( "sti\n\t"
  61                                            "stc\n\t"
  62                                            "int $0x15\n\t"
  63                                            "pushfw\n\t"
  64                                            "popw %w0\n\t"
  65                                            "cli\n\t" )
  66                                : "=r" ( flags ), "=a" ( discard_a )
  67                                : "a" ( Enable_A20 ) );
  68
  69         if ( flags & CF ) {
  70                 /* INT 15 method failed, try alternatives */
  71 #ifdef  IBM_L40
  72                 outb(0x2, 0x92);
  73 #else   /* IBM_L40 */
  74                 empty_8042();
  75                 outb(KC_CMD_WOUT, K_CMD);
  76                 empty_8042();
  77                 outb(KB_SET_A20, K_RDWR);
  78                 empty_8042();
  79 #endif  /* IBM_L40 */
  80         }
  81
  82         reentry_guard = 0;
  83 }
  84
  85 void gateA20_unset ( void ) {
  86         /* Not currently implemented */
  87 }