duskos

commit 4233cb64177d65225be7103509a11905b43befde
parent 7a600617da64d1cbd324239190519fa1b12017db
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Sun,  6 Nov 2022 12:26:57 -0500

drv/pc/a20: add A20 enabling method through PS/2

This has been tested on real hardware with A20 initially not enabled.

Diffstat:
M
fs/drv/pc/a20.fs
 | 
20
+++++++++++++++++---

1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/fs/drv/pc/a20.fs b/fs/drv/pc/a20.fs
@@ -1,12 +1,26 @@
 \ A20 line unlocking
+?f<< /asm/i386.fs
 
 \ Is A20 line enabled?
 : a20? $7dfe @ $107dfe @ <> ;
 
-\ TODO: add A20 mitigation. In QEMU, the line is already active, so I can't
-\ verify tweaks I would write here.
+code _wait pc al $64 i) in, al 2 i) test, abs>rel jnz, ret,
+code _wait2 pc al $64 i) in, al 1 i) test, abs>rel jz, ret,
+: _cmd ( n -- ) ['] _wait abs>rel call, al i) mov, al $64 i) out, ;
+code _unlockThroughPS2
+  cli, $ad _cmd $d0 _cmd
+  ' _wait2 abs>rel call,
+  al $60 i) in, ax push,
+  $d1 _cmd
+  ' _wait abs>rel call,
+  ax pop, al 2 i) or, al $60 i) out,
+  $ae _cmd
+  ' _wait abs>rel call,
+  sti, ret,
 
 32 $400 $400 * * const MEMTOP \ 32 MB ought to be enough for anybody
 
-: a20$ a20? not if abort" A20 line can't be activated" then
+: a20$
+  a20? not if _unlockThroughPS2 then
+  a20? not if abort" A20 line can't be activated" then
   $100000 to here MEMTOP HEREMAX ! ;