Reading A Byte of SMBus EEPROM Data
The following steps have to be followed for the System BIOS to read a byte of the Serial Presence Detect (SPD) data from the DIMM.
1.Program the SMBus Base Address Register, D31:F3:20h.
2.Set the I/O Space enable bit, D31:F3:04h[0].
3.Set the HST_EN bit, D31:F3:40h[0].
4.Clear the status bits by programming SMBBASE 00h to 1Eh.
5.Program the SMBus Transmit Slave Address Register with the DIMM SMBus address, SMBBASE 04h. For example: If the DIMM address is A2h and a byte is to be read from the DIMM, program SMBBASE 04h to A3h (A2h OR’ed with 1 (Read/Write bit)).
6.Program the SMBus Host Command Register with the DIMM’s SPD data offset to be read, SMBBASE 03h. For example: If reading from offset 04h in the DIMM’s SPD, this register will have a value of 04h (Offset of SPD data to be read).
7.Program the SMBus Host Control Register, SMBBASE 02h[7:0] to 48h.
8.Wait on the Host Busy (HOST_BUSY) bit to be clear in the Host Status Register, SMBBASE 00h[0]. The System BIOS should use the INTR bit, SMBBASE 00h[1] and the other error indicator bits in the SMBus Host Status Register to indicate the end of the operation before reading the SMBus data register.
9.After the HOST_BUSY bit is clear, check the DEV_ERR bit in the Host Status Register, SMBBASE 00h[2] = 0, if the HOST_BUSY bit is clear and the DEV_ERR bit is clear the BIOS can read the byte value from the SMBus Data 0 Register, SMBBASE 05h.
Step #1 to Step #3 will be programmed only once. The BIOS can follow Step #4 through Step#9 multiple times to get all the necessary EEPROM data from the SMBus devices.
源码（WIN-TC编译通过）：
#include
#include
unsigned SearchBAR(unsigned long address_s)
{
unsigned long int val;
asm mov dx,0xcf8
asm db 0x66
asm mov ax,address_s
asm db 0x66
asm out dx,ax
asm mov dx,0xcfc
asm db 0x66
asm in ax,dx
asm db 0x66
asm mov val,ax
return val;
}
void WriteFlags(unsigned long pci_addr,unsigned data)
{
asm mov dx,0xcf8
asm db 0x66
asm mov ax,pci_addr
asm db 0x66
asm out dx,ax
asm mov dx,0xcfc
asm mov al,data
asm out dx,al
}
unsigned ReadByte(unsigned SMBase_addr,unsigned i)
{
unsigned val;
outportb(SMBase_addr,0x1e);
outportb(SMBase_addr 0x04,0xa7);
outportb(SMBase_addr 0x03,i);
outportb(SMBase_addr 0x02,0x48);
while((inportb(SMBase_addr))&0x01){
delay(10);
}
val=inportb(SMBase_addr 0x05);
return val;
}
void main()
{
unsigned long pci_addr,SMBase_addr,bus,dev,func,offset;
unsigned i,data;
bus=0x00;
dev=0x1f;
func=0x03;
pci_addr=0x80000000 (bus<<16) (dev<<11) (func<<8);
WriteFlags(pci_addr 0x04,0x03);
WriteFlags(pci_addr 0x40,0x11);
SMBase_addr=SearchBAR(pci_addr 0x20)&0xffe0;
printf("PCI Address:%x",pci_addr>>16);
printf("%x ",pci_addr);
printf("use IO :%x ",SMBase_addr);
printf("Read Byte: ");
for(i=0;i<</SPAN>64;i ){
data=ReadByte(SMBase_addr,i);
printf("%4x",data);
if(i%16==15)
printf(" ");
}
getchar();
}
转载：http://blog.sina.com.cn/s/blog_870045320102v60u.html