diff options
Diffstat (limited to 'i386/pc/i16/i16_raw_test_a20.S')
| -rw-r--r-- | i386/pc/i16/i16_raw_test_a20.S | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/i386/pc/i16/i16_raw_test_a20.S b/i386/pc/i16/i16_raw_test_a20.S new file mode 100644 index 00000000..a934e12f --- /dev/null +++ b/i386/pc/i16/i16_raw_test_a20.S @@ -0,0 +1,35 @@ + +#include <mach/machine/asm.h> + + .text + .code16 + +/* + * Test the A20 address line; return true if it is enabled. + */ +ENTRY(i16_raw_test_a20) + xorw %ax,%ax + movw %ax,%fs + notw %ax + movw %ax,%gs + + /* See if the values in already in the corresponding locations + are the same. */ + movw %fs:0,%ax + cmpw %gs:16,%ax + jnz 1f + + /* Yes; try changing one and see if they're still the same. */ + movw %ax,%dx + notw %ax + movw %ax,%fs:0 + cmpw %gs:16,%ax + movw %dx,%fs:0 + jnz 1f + + xorl %eax,%eax + ret +1: + movl $1,%eax + ret + |