Intel 815 manual Initialization and Usage of Stolen Memory

Models: 815

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Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

R

Bit

Description

 

 

1

SMM Space Locked (D_LCK). When D_LCK is set to 1 then D_LCK, GMS, USMM, and the most

 

significant bit of LSMM become read only. D_LCK can be set to 1 via a normal configuration space

 

write but can only be cleared by a reset. The combination of D_LCK and LSMM provide convenience

 

with security. The BIOS can use LSMM=01 to initialize SMM space and then use D_LCK to “lock

 

down” SMM space in the future so that no application software (or BIOS itself) can violate the

 

integrity of SMM space, even if the program has knowledge of the LSMM function. This bit also

 

Locks the DRP and DRP2 registers.

 

 

0

E_SMRAM_ERR (E_SMERR). This bit is set when processor accesses the defined memory ranges

 

in Extended SMRAM (HSEG or TSEG) while not in SMM mode. It is software’s responsibility to clear

 

this bit. The software must write a 1 to this bit to clear it This bit is Not set for the case of an Explicit

 

Write Back operation.

 

 

Initialization and Usage of “Stolen” Memory

SMRAM Register Bits 7:4 control the theft of memory from Main Memory space for use as Graphics Local Memory and SMM TSEG memory. The blocks of memory selected by these fields are NOT accessible as general system RAM. When Bit 5 of the SMRAM register is a “1” the TSEG segment of memory can ONLY be accessed by the processor in SMM mode (No other agent can access this memory). Therefore, BIOS should initialize this block of memory BEFORE setting either Bit 5 or Bit 7 of the SMRAM register. The memory for TSEG is “Stolen” first and then the Graphics Local Memory is “Stolen”. An example of this theft mechanism is:

TOM equal 64 MB,

TSEG selected as 512 KB in size,

Graphics Local Memory selected as 1 MB in size

General System RAM available in system = 62.5 MB

 General System RAM Range

00000000h to 03E7FFFFh

TSEG Address Range

03F80000h to 03FFFFFFh

TSEG “Stolen” from

03F80000h to 03FFFFFFh

 Graphics Local Memory “Stolen” from

03E80000h to 03F7FFFFh

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Page 71
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Intel 815 manual Initialization and Usage of Stolen Memory