diff options
| author | H. Peter Anvin <hpa@zytor.com> | 2008-06-27 22:29:13 +0100 |
|---|---|---|
| committer | Michael Brown <mcb30@etherboot.org> | 2008-06-27 22:29:13 +0100 |
| commit | b7882065f5319d8d8f93eb4b879d816bb47bfe3a (patch) | |
| tree | 8ec8ab67ff0baf31c1580b0c7abbca5b78695042 /src/arch | |
| parent | 2b9e7a4767b73cfe10324fbc2fed07646ee4a33c (diff) | |
| download | ipxe-b7882065f5319d8d8f93eb4b879d816bb47bfe3a.tar.gz | |
[a20] Send a null command to the KBC after changing A20
Send a null command, specifically "pulse outputs" with no outputs
selected, to the KBC after changing A20. This was apparently done by DOS,
presumably as a synchronization hack, and the authors of the UHCI spec
thought it was inherent. Therefore, there are systems out there (e.g. HP
DL360 G5) which will stop responsing to "legacy USB" unless they see the
null command, 0xFF, written to port 0x64 at the end of the A20 toggling
sequence.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'src/arch')
| -rw-r--r-- | src/arch/i386/firmware/pcbios/gateA20.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/src/arch/i386/firmware/pcbios/gateA20.c b/src/arch/i386/firmware/pcbios/gateA20.c index 2caac894..a14e3416 100644 --- a/src/arch/i386/firmware/pcbios/gateA20.c +++ b/src/arch/i386/firmware/pcbios/gateA20.c @@ -12,6 +12,7 @@ #define KC_CMD_WIN 0xd0 /* read output port */ #define KC_CMD_WOUT 0xd1 /* write output port */ +#define KC_CMD_NULL 0xff /* null command ("pulse nothing") */ #define KB_SET_A20 0xdf /* enable A20, enable output buffer full interrupt enable data line @@ -130,6 +131,8 @@ void gateA20_set ( void ) { empty_8042(); outb ( KB_SET_A20, K_RDWR ); empty_8042(); + outb ( KC_CMD_NULL, K_CMD ); + empty_8042(); if ( gateA20_is_set ( A20_KBC_RETRIES ) ) { DBG ( "Enabled gate A20 using " "keyboard controller\n" ); |