How to power down the computer from a freestanding environment?
from http://forum.osdev.org/viewtopic.php?t=16990
The ACPI shutdown is technically a really simple thing all that is needed is a outw(PM1a_CNT, SLP_TYPa | SLP_EN ); and the computer is powered off. The problem lies in the gathering of these values especially since the SLP_TYPa is in the _S5 object which is in the DSDT and therefore AML encoded.
Below is a simple "map" of where to find these fields.
"RSD PTR "
||
RsdtAddress pointer at offset 16
||
\/
"RSDT"
||
pointer at offset 36 + 4 * n (check the target for the sig "FACP" to get the right n)
||
\/
"FACP"
||
||=====\
|| ||
|| PM1a_CNT_BLK; offset: 64 (see section 4.7.3.2)
|| PM1b_CNT_BLK; offset: 68
|| ||
|| \/
|| SLP_TYPx; bit 10-12
|| SLP_EN; bit 13
||
DSDT pointer at offset 40
||
\/
"DSDT" (export the \_S5 object somehow.)
To export the \_S5 object one would normally use an AML interpreter but that's obviously not an option considering we're building a hobby OS. The simple solution is to scan the DSDT manually. The AML language specifies that _... objects are defined only once which makes it very simple to find the \_S5 object since a simple memcmp() is enough.
Once found the SLP_TYPx values are extracted.
bytecode of the \_S5 object
-----------------------------------------
| (optional) | | | |
NameOP | \ | _ | S | 5 | _
08 | 5A | 5F | 53 | 35 | 5F
-----------------------------------------------------------------------------------------------------------
| | | ( SLP_TYPa ) | ( SLP_TYPb ) | ( Reserved ) | (Reserved )
PackageOP | PkgLength | NumElements | byteprefix Num | byteprefix Num | byteprefix Num | byteprefix Num
12 | 0A | 04 | 0A 05 | 0A 05 | 0A 05 | 0A 05
----this-structure-was-also-seen----------------------
PackageOP | PkgLength | NumElements |
12 | 06 | 04 | 00 00 00 00
The gathering of the information is best performed at OS initialization because after that you can reuse the ram and don't need to worry about corrupting it.
Now all that remains is outw(PM1a_CNT, SLP_TYPa | SLP_EN ); and you're gone.
If PM1b_CNT != 0 you need to repeat it with b.
If that was a little too abstract here is some code to look at
//
// here is the slighlty complicated ACPI poweroff code
//
#include <stddef.h>
#include <print.h>
#include <string.h>
#include <io.h>
#include <time.h>
dword *SMI_CMD;
byte ACPI_ENABLE;
byte ACPI_DISABLE;
dword *PM1a_CNT;
dword *PM1b_CNT;
word SLP_TYPa;
word SLP_TYPb;
word SLP_EN;
word SCI_EN;
byte PM1_CNT_LEN;
struct RSDPtr
{
byte Signature[8];
byte CheckSum;
byte OemID[6];
byte Revision;
dword *RsdtAddress;
};
struct FACP
{
byte Signature[4];
dword Length;
byte unneded1[40 - 8];
dword *DSDT;
byte unneded2[48 - 44];
dword *SMI_CMD;
byte ACPI_ENABLE;
byte ACPI_DISABLE;
byte unneded3[64 - 54];
dword *PM1a_CNT_BLK;
dword *PM1b_CNT_BLK;
byte unneded4[89 - 72];
byte PM1_CNT_LEN;
};
// check if the given address has a valid header
unsigned int *acpiCheckRSDPtr(unsigned int *ptr)
{
char *sig = "RSD PTR ";
struct RSDPtr *rsdp = (struct RSDPtr *) ptr;
byte *bptr;
byte check = 0;
int i;
if (memcmp(sig, rsdp, 8) == 0)
{
// check checksum rsdpd
bptr = (byte *) ptr;
for (i=0; i<sizeof(struct RSDPtr); i++)
{
check += *bptr;
bptr++;
}
// found valid rsdpd
if (check == 0) {
/*
if (desc->Revision == 0)
wrstr("acpi 1");
else
wrstr("acpi 2");
*/
return (unsigned int *) rsdp->RsdtAddress;
}
}
return NULL;
}
// finds the acpi header and returns the address of the rsdt
unsigned int *acpiGetRSDPtr(void)
{
unsigned int *addr;
unsigned int *rsdp;
// search below the 1mb mark for RSDP signature
for (addr = (unsigned int *) 0x000E0000; (int) addr<0x00100000; addr += 0x10/sizeof(addr))
{
rsdp = acpiCheckRSDPtr(addr);
if (rsdp != NULL)
return rsdp;
}
// at address 0x40:0x0E is the RM segment of the ebda
int ebda = *((short *) 0x40E); // get pointer
ebda = ebda*0x10 &0x000FFFFF; // transform segment into linear address
// search Extended BIOS Data Area for the Root System Description Pointer signature
for (addr = (unsigned int *) ebda; (int) addr<ebda+1024; addr+= 0x10/sizeof(addr))
{
rsdp = acpiCheckRSDPtr(addr);
if (rsdp != NULL)
return rsdp;
}
return NULL;
}
// checks for a given header and validates checksum
int acpiCheckHeader(unsigned int *ptr, char *sig)
{
if (memcmp(ptr, sig, 4) == 0)
{
char *checkPtr = (char *) ptr;
int len = *(ptr + 1);
char check = 0;
while (0<len--)
{
check += *checkPtr;
checkPtr++;
}
if (check == 0)
return 0;
}
return -1;
}
int acpiEnable(void)
{
// check if acpi is enabled
if ( (inw((unsigned int) PM1a_CNT) &SCI_EN) == 0 )
{
// check if acpi can be enabled
if (SMI_CMD != 0 && ACPI_ENABLE != 0)
{
outb((unsigned int) SMI_CMD, ACPI_ENABLE); // send acpi enable command
// give 3 seconds time to enable acpi
int i;
for (i=0; i<300; i++ )
{
if ( (inw((unsigned int) PM1a_CNT) &SCI_EN) == 1 )
break;
sleep(10);
}
if (PM1b_CNT != 0)
for (; i<300; i++ )
{
if ( (inw((unsigned int) PM1b_CNT) &SCI_EN) == 1 )
break;
sleep(10);
}
if (i<300) {
wrstr("enabled acpi.\n");
return 0;
} else {
wrstr("couldn't enable acpi.\n");
return -1;
}
} else {
wrstr("no known way to enable acpi.\n");
return -1;
}
} else {
//wrstr("acpi was already enabled.\n");
return 0;
}
}
//
// bytecode of the \_S5 object
// -----------------------------------------
// | (optional) | | | |
// NameOP | \ | _ | S | 5 | _
// 08 | 5A | 5F | 53 | 35 | 5F
//
// -----------------------------------------------------------------------------------------------------------
// | | | ( SLP_TYPa ) | ( SLP_TYPb ) | ( Reserved ) | (Reserved )
// PackageOP | PkgLength | NumElements | byteprefix Num | byteprefix Num | byteprefix Num | byteprefix Num
// 12 | 0A | 04 | 0A 05 | 0A 05 | 0A 05 | 0A 05
//
//----this-structure-was-also-seen----------------------
// PackageOP | PkgLength | NumElements |
// 12 | 06 | 04 | 00 00 00 00
//
// (Pkglength bit 6-7 encode additional PkgLength bytes [shouldn't be the case here])
//
int initAcpi(void)
{
unsigned int *ptr = acpiGetRSDPtr();
// check if address is correct ( if acpi is available on this pc )
if (ptr != NULL && acpiCheckHeader(ptr, "RSDT") == 0)
{
// the RSDT contains an unknown number of pointers to acpi tables
int entrys = *(ptr + 1);
entrys = (entrys-36) /4;
ptr += 36/4; // skip header information
while (0<entrys--)
{
// check if the desired table is reached
if (acpiCheckHeader((unsigned int *) *ptr, "FACP") == 0)
{
entrys = -2;
struct FACP *facp = (struct FACP *) *ptr;
if (acpiCheckHeader((unsigned int *) facp->DSDT, "DSDT") == 0)
{
// search the \_S5 package in the DSDT
char *S5Addr = (char *) facp->DSDT +36; // skip header
int dsdtLength = *(facp->DSDT+1) -36;
while (0 < dsdtLength--)
{
if ( memcmp(S5Addr, "_S5_", 4) == 0)
break;
S5Addr++;
}
// check if \_S5 was found
if (dsdtLength > 0)
{
// check for valid AML structure
if ( ( *(S5Addr-1) == 0x08 || ( *(S5Addr-2) == 0x08 && *(S5Addr-1) == '\\') ) && *(S5Addr+4) == 0x12 )
{
S5Addr += 5;
S5Addr += ((*S5Addr &0xC0)>>6) +2; // calculate PkgLength size
if (*S5Addr == 0x0A)
S5Addr++; // skip byteprefix
SLP_TYPa = *(S5Addr)<<10;
S5Addr++;
if (*S5Addr == 0x0A)
S5Addr++; // skip byteprefix
SLP_TYPb = *(S5Addr)<<10;
SMI_CMD = facp->SMI_CMD;
ACPI_ENABLE = facp->ACPI_ENABLE;
ACPI_DISABLE = facp->ACPI_DISABLE;
PM1a_CNT = facp->PM1a_CNT_BLK;
PM1b_CNT = facp->PM1b_CNT_BLK;
PM1_CNT_LEN = facp->PM1_CNT_LEN;
SLP_EN = 1<<13;
SCI_EN = 1;
return 0;
} else {
wrstr("\\_S5 parse error.\n");
}
} else {
wrstr("\\_S5 not present.\n");
}
} else {
wrstr("DSDT invalid.\n");
}
}
ptr++;
}
wrstr("no valid FACP present.\n");
} else {
wrstr("no acpi.\n");
}
return -1;
}
void acpiPowerOff(void)
{
// SCI_EN is set to 1 if acpi shutdown is possible
if (SCI_EN == 0)
return;
acpiEnable();
// send the shutdown command
outw((unsigned int) PM1a_CNT, SLP_TYPa | SLP_EN );
if ( PM1b_CNT != 0 )
outw((unsigned int) PM1b_CNT, SLP_TYPb | SLP_EN );
wrstr("acpi poweroff failed.\n");
}
For further information read the corresponding sections of the ACPI 1.0a specification
9.1.7 Transitioning from the Working to the Soft Off State
7.5.2 \_Sx states
7.4.1 \_S5
4.7.2.3 Sleeping/Wake Control
16.3 AML Byte Streeam Byte Values
16.2.3 Package Length Encoding
This works on all of my machines bochs and qemu. but I noticed that one needn't enable ACPI for the pc to power down. Though i don't know if this is always the case.
If you just want to play a little.
For bochs and qemu it's outw( 0xB004, 0x0 | 0x2000 );