Intel 845 3.5.33 TOMTop of Low Memory Register (Device 0)

Register Description

R

Intel® 82845 MCH for SDR Datasheet 73

3.5.33 TOM—Top of Low Memory Register (Device 0)

Address Offset: C4–C5h

Default Value: 0100h

Access: R/W

Size: 16 bits

This register contains the maximum address below 4 GB that should be treated as a memory

access. Note that this register must be set to a value of 0100h (16 MB) or greater. Usually it will

sit below the areas configured for the hub interface, PCI memory, and the graphics aperture.

Bit Description

15:4 Top of Low Memory (TOM). This register contains the address that corresponds to bits 31 to

20 of the maximum system memory address that lies below 4 GB. Conf i gurat i on s oftware

should set this value to either the maximum amount of memory i n t he system or to the

minimum address allocated for PCI memory or the graphics apert ure, whichever is smaller.

Programming Example: 400h = 1 GB. An access to 4000_0000h or above will be considered

above the TOM and therefore not routed to system memory. It may go to AGP, aperture, or

subtractively decode to the hub interface.

3:0 Reserved.

Contents

Main Intel 845 Chipset: 82845 Memory Controller Hub (MCH) for SDR Page Contents Page Page Page Figures Tables Revision History Intel 82845 MCH Features 10 Intel 82845 MCH for SDR Datasheet System Block Diagram 1 Introduction 1.1 Terminology and Notations Page 1.2 Reference Documents 1.3 Intel 845 Chipset System Architecture Intel 82801BA I/O Controller Hub 2 (ICH2) 1.4 Intel 82845 MCH Overview 1.4.1 System Bus Interface 1.4.2 System Bus Error Checking 1.4.3 System Memory Interface 1.4.4 AGP Interface 1.4.5 Hub Interface 1.4.6 Intel MCH Clocking 1.4.7 System Interrupts 1.4.8 Powerdown Flow 2 Signal Description Signal Description 20 Intel 82845 MCH for SDR Datasheet Figure 1. Intel MCH Simplified Block Diagram 2.1 System Bus Signals Page 2.2 SDR SDRAM Interface Signals 2.3 Hub Interface Signals 2.4 AGP Interface Signals 2.4.1 AGP Addressing Signals 2.4.2 AGP Flow Control Signal s 2.4.3 AGP Status Signals Signal Description 26 Intel 82845 MCH for SDR Datasheet 2.4.4 AGP Strobes Signals 2.4.5 AGP/PCI Signals Page 2.5 Clocks, Reset, and Miscellaneous Signals 2.6 Voltage Reference and Power Signals Signal Description 30 Intel 82845 MCH for SDR Datasheet 2.7 Reset States During Reset 3 Register Description 3.1 Register Terminology 3.2 PCI Bus Configuration Space Access 3.2.1 Standard PCI Bus Configuration Mechanism 3.2.2 Routing Configuration Accesses PCI Bus 0 Configuration Mechanism Primary PCI and Downstream Configuration Mechanism AGP Configuration Mechanism 3.3 I/O Mapped Registers 3.3.1 CONF_ADDRConfiguration Address Register Page 3.3.2 CONF_DATAConfiguration Data Register 3.4 Memory-Mapped Register Space 3.4.1 DRAMWIDTHDRAM Width Register 3.4.2 DQCMDSTRStrength Control Register (SDQ and CMD Signal Groups) 3.4.3 CKESTRStrength Control Register (SCKE Signal Group) 3.4.4 CSBSTRStrength Control Register (SCS# Si gnal Group) 3.4.5 CKSTRStrength Control Register (Cl ock Si gnal Group) 3.4.6 RCVENSTRStrength Control Register (RCVENOUT Signal Group) Register Description Intel 82845 MCH for SDR Datasheet 43 3.5 Host-Hub Interface Bridge Device Registers (Device 0) Page 3.5.1 VIDVendor Identificati on Regi ster (Device 0) 3.5.2 DIDDevice Identification Register (Device 0) 3.5.3 PCICMDPCI Command Register (Device 0) 3.5.4 PCISTSPCI Status Register (Device 0) 3.5.5 RIDRevision Identification Register (Device 0) 3.5.6 SUBCSub-Class Code Register (Device 0) 3.5.7 BCCBase Class Code Register (Device 0) 3.5.8 MLTMaster Latency Timer Register (Device 0) 3.5.9 HDRHeader Type Register (Device 0) 3.5.10 APBASEAperture Base Configuration Register (Device 0) 3.5.11 SVIDSubsystem Vendor Identification (Device 0) 3.5.12 SIDSubsystem Identification (Device 0) 3.5.13 CAPPTRCapabilities Pointer (Device 0) 3.5.14 AGPMAGP Miscellaneous Configurati on Regi ster (Device 0) 3.5.15 DRB[0:7]DRAM Row Boundary Registers (Device 0) 3.5.16 DRADRAM Row Attribute Registers (Device 0) Page 3.5.17 DRTDRAM Timing Register (Device 0) 3.5.18 DRCDRAM Controller Mode Register (Device 0) Page 3.5.19 DERRSYNDRAM Error Syndrome Register (Device 0) 3.5.20 EAPError Address Pointer Register (Device 0) 3.5.21 PAM[0:6]Programmable Attribute Map Registers (Device 0) Page DOS Application Area (00000h9FFFh) Video Buffer Area (A0000hBFFFFh) Expansion Area (C0000hDFFFFh) Extended System BIOS Area (E0000hEFFFFh) System BIOS Area (F0000hFFFFFh) 3.5.22 FDHCFixed DRAM Hole Contr ol Regi ster (Device 0) 3.5.23 SMRAMSystem Management RAM Control Register (Device 0) 3.5.24 ESMRAMCExtended System Mgmt RAM Control Register (Device 0) 3.5.25 ACAPIDAGP Capability Identifier Register (Device 0) 3.5.26 AGPSTATAGP Status Register (Device 0) 3.5.27 AGPCMDAGP Command Register (Device 0) 3.5.28 AGPCTRLAGP Control Register (Device 0) 3.5.29 APSIZEAperture Size (Device 0) 3.5.30 ATTBASEAperture Translation Table Base Register (Device 0) 3.5.31 AMTTAGP Interface Multi-Transaction Timer Register (Device 0) 3.5.32 LPTTAGP Low Priority Transaction Timer Register (Device 0) 3.5.33 TOMTop of Low Memory Register (Device 0) 3.5.34 MCHCFGMCH Configuration Register (Device 0) 3.5.35 ERRSTSError Status Register (Device 0) 3.5.36 ERRCMDError Command Register (Device 0) Page 3.5.37 SMICMDSMI Command Register (Device 0) 3.5.38 SCICMDSCI Command Register (Device 0) 3.5.39 SKPDScratchpad Data Register (Device 0) 3.5.40 CAPIDProduct Specific Capability Identifier Register (Device 0) 3.6 Bridge Registers (Device 1) 3.6.1 VID1Vendor Identificati on Regi ster (Device 1) 3.6.2 DID1Device Identification Register (Device 1) 3.6.3 PCICMD1PCI-PCI Command Register (Device 1) 3.6.4 PCISTS1PCI-PCI Status Register (Device 1) 3.6.5 RID1Revision Identification Register (Device 1) 3.6.6 SUBC1Sub-Class Code Register (Device 1) 3.6.7 BCC1Base Class Code Register (Device 1) 3.6.8 MLT1Master Latency Timer Register (Device 1) 3.6.9 HDR1Header Type Register (Device 1) 3.6.10 PBUSN1Primary Bus Number Register (Device 1) 3.6.11 SBUSN1Secondary Bus Number Register (Device 1) 3.6.12 SUBUSN1Subordi nate Bus Number Register (Device 1) 3.6.13 SMLT1Secondary Master Latency Timer Register (Device 1) 3.6.14 IOBASE1I/O Base Address Register (Device 1) 3.6.15 IOLIMIT1I/O Limit Address Register (Device 1) 3.6.16 SSTS1Secondary PCI-PCI Status Register (Device 1) 3.6.17 MBASE1Memory Base Address Register (Device 1) 3.6.18 MLIM IT1Memory Limit Address Register (Device 1) 3.6.19 PMBASE1Prefetchable Memory Base Address Register (Device 1) 3.6.20 PMLIMIT1Prefetchable Memory Limit Address Register (Device 1) 3.6.21 BCTRL1PCI-PCI Bridge Control Register (Device 1) 3.6.22 ERRCMD1Error Command Register (Device 1) 3.6.23 DWTCDRAM Write Ther mal Management Control Register (Device 1) 3.6.24 DRTCDRAM Read Thermal Management Control Register (Device 1) Page 4 System Address Map 4.1 Memory Address Ranges System Address Map 98 Intel 82845 MCH for SDR Datasheet Figure 4. DOS Compatible Area Address Map 4.1.1 VGA and MDA Memory Space 4.1.2 PAM Memory Spaces 4.1.3 ISA Hole Memory Space 4.1.4 TSEG SMM Memory Space 4.1.5 IOAPIC Memory Space 4.1.6 System Bus Interrupt APIC Memory Space 4.1.7 High SMM Memory Space 4.1.8 AGP Aperture Space (Device 0 BAR) 4.2 AGP Memory Address Ranges 4.2.1 AGP DRAM Graphics Aperture 4.3 System Management Mode (SMM) Memory Range 4.3.1 SMM Space Definition 4.3.2 SMM Space Restrictions 4.4 I/O Address Space 4.5 Intel MCH Decode Rules and Cross-Bridge Address Mapping 4.5.1 Hub Interface Decode Rules 4.5.2 AGP Interface Decode Rules Cycles Initiated Using AGP FRAME# Protocol Cycles Initiated Using AGP PIPE# or SB Protocol AGP Accesses to MCH that Cross Device Boundaries 5 Functional Description 5.1 System Bus 5.1.1 Dynamic Bus Inversion 5.1.2 System Bus Interrupt Delivery 5.1.3 Upstream Interrupt Messages 5.2 System Memory Interface 5.2.1 Single Data Rate (SDR) SDRAM Interface Overview 5.2.2 Memory Organization and Configur ation 5.2.2.1 Configuration Mechanism For DIMMs Memory Detection and Initialization SMBus Configuration and Access of the Serial Presence Detect Ports Memory Register Programming 5.2.3 Memory Address Translation and Decoding 5.2.4 DRAM Performance Description 5.2.4.1 Data Integrity (ECC) 5.3 AGP Interface Overview 5.3.1 AGP Target Operations Page 5.3.2 AGP Transaction Ordering 5.3.3 AGP Signal Levels 5.3.4 4x AGP Protocol 5.3.5 Fast Writes 5.3.6 AGP FRAME# Transactions on AGP MCH Initiator and Target Operations Page MCH Retry/Disconnect Conditions Delayed Transaction 5.4 Power and Thermal Management 5.4.1 Processor Power State Control 5.4.2 Sleep State Control 5.5 Intel MCH Clocking 5.6 Intel MCH System Reset and Power Sequencing 6 Electrical Characteristics 6.1 Absolute Maximum Ratings 6.2 Power Characteristics 6.3 Signal Groups Page Electrical Characteristics 122 Intel 82845 MCH for SDR Datasheet 6.4 DC Characteristics Table 21. DC Characteristics Electrical Characteristics Intel 82845 MCH for SDR Datasheet 123 Page 7 Ballout and Package Information Ballout and Package Information 126 Intel 82845 MCH for SDR Datasheet Figure 6. Intel 82845 MCH Ballout Diagram (Top ViewLeft Side) Ballout and Package Information Intel 82845 MCH for SDR Datasheet 127 Figure 7. Intel 82845 MCH Ballout Diagram (Top ViewRight Side) Ballout and Package Information 128 Intel 82845 MCH for SDR Datasheet Table 22. Intel 82845 MCH Ballout Listed Alphabetically by Signal Name Page Page Page Page Page 7.1 Package Mechanical Information Ballout and Package Information Intel 82845 MCH for SDR Datasheet 135 Figure 9. Intel MCH FC-BGA Package Dimensions (Bottom View) Page 8 Testability 8.1 XOR Test Mode Initialization 8.2 XOR Chains Page Testability 140 Intel 82845 MCH for SDR Datasheet Table 24. XOR Chain 1 Testability Intel 82845 MCH for SDR Datasheet 141 Table 25. XOR Chain 2 Testability 142 Intel 82845 MCH for SDR Datasheet Table 26. XOR Chain 3 Testability Intel 82845 MCH for SDR Datasheet 143 Table 27. XOR Chain 4 Testability 144 Intel 82845 MCH for SDR Datasheet Table 28. XOR Chain 5 Page Testability 146 Intel 82845 MCH for SDR Datasheet Table 29. XOR Chain 6 Testability Intel 82845 MCH for SDR Datasheet 147 Table 30. XOR Chain 7