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         unsigned long time;
  32
  33         time = currticks() + TICKS_PER_SEC;     /* max wait of 1 second */
  34         while ( ( inb ( K_CMD ) & K_IBUF_FUL ) &&
  35                 currticks() < time ) {
  36                 /* Do nothing.  In particular, do *not* read from
  37                  * K_RDWR, because that will drain the keyboard buffer
  38                  * and lose keypresses.
  39                  */
  40         }
  41 }
  42 #endif  /* IBM_L40 */
  43
  44 /*
  45  * Gate A20 for high memory
  46  *
  47  * Note that this function gets called as part of the return path from
  48  * librm's real_call, which is used to make the int15 call if librm is
  49  * being used.  To avoid an infinite recursion, we make gateA20_set
  50  * return immediately if it is already part of the call stack.
  51  */
  52 void gateA20_set ( void ) {
  53         static char reentry_guard = 0;
  54         unsigned int discard_a;
  55         unsigned int flags;
  56
  57         if ( reentry_guard )
  58                 return;
  59         reentry_guard = 1;
  60
  61         __asm__ __volatile__ ( REAL_CODE ( "sti\n\t"
  62                                            "stc\n\t"
  63                                            "int $0x15\n\t"
  64                                            "pushfw\n\t"
  65                                            "popw %w0\n\t"
  66                                            "cli\n\t" )
  67                                : "=r" ( flags ), "=a" ( discard_a )
  68                                : "a" ( Enable_A20 ) );
  69
  70
  71         if ( flags & CF ) {
  72                 /* INT 15 method failed, try alternatives */
  73 #ifdef  IBM_L40
  74                 outb(0x2, 0x92);
  75 #else   /* IBM_L40 */
  76                 empty_8042();
  77                 outb(KC_CMD_WOUT, K_CMD);
  78                 empty_8042();
  79                 outb(KB_SET_A20, K_RDWR);
  80                 empty_8042();
  81 #endif  /* IBM_L40 */
  82         }
  83
  84         reentry_guard = 0;
  85 }
  86
  87 void gateA20_unset ( void ) {
  88         /* Not currently implemented */
  89 }