Local Vector Table (LVT)

Relevant source files

src/lvt.rs

src/regs/lvt/mod.rs

Purpose and Scope

This document covers the Local Vector Table (LVT) subsystem within the x86_vlapic crate, which manages interrupt vector configuration for various local interrupt sources in the virtual Local APIC implementation. The LVT provides a standardized interface for configuring how different types of interrupts (timer, thermal, performance monitoring, external pins, errors) are delivered to the processor.

For detailed information about individual LVT register implementations, see Timer LVT Register, External Interrupt Pin Registers, System Monitoring LVT Registers, and Error Handling LVT Registers. For broader APIC register system context, see Register System.

LVT Architecture Overview

The Local Vector Table consists of seven specialized registers that control different interrupt sources within the Local APIC. Each register follows a common structural pattern while providing source-specific functionality.

LVT Register Layout

flowchart TD
subgraph subGraph4["LocalVectorTable Struct"]
    LVT["LocalVectorTable"]
    subgraph subGraph3["Error Handling"]
        ERROR["lvt_errLvtErrorRegisterLocal0x370"]
    end
    subgraph subGraph2["External Pin Sources"]
        LINT0["lvt_lint0LvtLint0RegisterLocalFEE0_0350H"]
        LINT1["lvt_lint1LvtLint1RegisterLocalFEE0_0360H"]
    end
    subgraph subGraph1["Timer Source"]
        TIMER["lvt_timerLvtTimerRegisterLocalFEE0_0320H"]
    end
    subgraph subGraph0["System Monitoring Sources"]
        CMCI["lvt_cmciLvtCmciRegisterLocalFEE0_02F0H"]
        THERMAL["lvt_thermalLvtThermalMonitorRegisterLocalFEE0_0330H"]
        PERFCNT["lvt_perf_countLvtPerformanceCounterRegisterLocalFEE0_0340H"]
    end
end

LVT --> CMCI
LVT --> ERROR
LVT --> LINT0
LVT --> LINT1
LVT --> PERFCNT
LVT --> THERMAL
LVT --> TIMER

Sources: src/lvt.rs(L9 - L24)

Register Address Mapping

The LVT registers are mapped to specific offsets within the APIC register space:

Register	Type	Address Offset	Purpose
lvt_cmci	LvtCmciRegisterLocal	FEE0_02F0H	Corrected Machine Check Interrupts
lvt_timer	LvtTimerRegisterLocal	FEE0_0320H	Local APIC Timer
lvt_thermal	LvtThermalMonitorRegisterLocal	FEE0_0330H	Thermal Monitoring
lvt_perf_count	LvtPerformanceCounterRegisterLocal	FEE0_0340H	Performance Counter Overflow
lvt_lint0	LvtLint0RegisterLocal	FEE0_0350H	External Interrupt Pin 0
lvt_lint1	LvtLint1RegisterLocal	FEE0_0360H	External Interrupt Pin 1
lvt_err	LvtErrorRegisterLocal	0x370	APIC Error Conditions

Sources: src/lvt.rs(L10 - L23)

Common LVT Structure and Functionality

All LVT registers share a common architectural pattern using the *RegisterLocal type structure, which provides local cached copies of register values. This design enables efficient access while maintaining consistency with the underlying APIC register model.

Initialization Pattern

flowchart TD
DEFAULT["Default::default()"]
RESET_VALUE["RESET_LVT_REG"]
CMCI_INIT["LvtCmciRegisterLocal::new()"]
TIMER_INIT["LvtTimerRegisterLocal::new()"]
THERMAL_INIT["LvtThermalMonitorRegisterLocal::new()"]
PERF_INIT["LvtPerformanceCounterRegisterLocal::new()"]
LINT0_INIT["LvtLint0RegisterLocal::new()"]
LINT1_INIT["LvtLint1RegisterLocal::new()"]
ERROR_INIT["LvtErrorRegisterLocal::new()"]

DEFAULT --> RESET_VALUE
RESET_VALUE --> CMCI_INIT
RESET_VALUE --> ERROR_INIT
RESET_VALUE --> LINT0_INIT
RESET_VALUE --> LINT1_INIT
RESET_VALUE --> PERF_INIT
RESET_VALUE --> THERMAL_INIT
RESET_VALUE --> TIMER_INIT

Sources: src/lvt.rs(L26 - L38)

All LVT registers are initialized with the same reset value RESET_LVT_REG, providing a consistent starting state across all interrupt sources. This ensures predictable behavior during system initialization and reset conditions.

Register Organization

The LVT implementation follows a modular architecture where each register type is implemented in its own module, promoting code organization and maintainability.

Module Structure

flowchart TD
subgraph src/regs/lvt/["src/regs/lvt/"]
    MOD["mod.rsPublic Interface"]
    subgraph subGraph0["Individual Register Modules"]
        CMCI_MOD["cmci.rsLvtCmciRegisterLocal"]
        ERROR_MOD["error.rsLvtErrorRegisterLocal"]
        LINT0_MOD["lint0.rsLvtLint0RegisterLocal"]
        LINT1_MOD["lint1.rsLvtLint1RegisterLocal"]
        PERFMON_MOD["perfmon.rsLvtPerformanceCounterRegisterLocal"]
        THERMAL_MOD["thermal.rsLvtThermalMonitorRegisterLocal"]
        TIMER_MOD["timer.rsLvtTimerRegisterLocal"]
    end
end

MOD --> CMCI_MOD
MOD --> ERROR_MOD
MOD --> LINT0_MOD
MOD --> LINT1_MOD
MOD --> PERFMON_MOD
MOD --> THERMAL_MOD
MOD --> TIMER_MOD

Sources: src/regs/lvt/mod.rs(L1 - L16)

Each module implements a specific LVT register type with its unique functionality while maintaining the common interface pattern. The mod.rs file serves as the public interface, re-exporting all register types for use by the LocalVectorTable struct.

Integration with Virtual APIC System

The LocalVectorTable is integrated into the broader virtual APIC register system through the VirtualApicRegs structure, where it manages all interrupt vector table functionality as a cohesive unit. This design separates interrupt configuration concerns from other APIC functionality while maintaining the standard APIC register interface.

Sources: src/lvt.rs(L1 - L39) src/regs/lvt/mod.rs(L1 - L16)

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