<< Click to Display Table of Contents >> Navigation:  ASA-EMulatR Reference Guide > Introduction > Architecture Overview > Chapter 15 – Memory System Implementation Details > 15.3 GuestMemory Region Support and PA Routing

15.3.1 PA Routing Table

 

GuestMemory maintains a QVector<PARouteEntry> routing table that maps contiguous physical address ranges to subsystems. Each PARouteEntry is an 8-byte-aligned structure containing the start PA, end PA (exclusive), a RouteTarget discriminator, and an offsetBase for PA-to-subsystem-offset translation. The entry provides contains(), containsRange(), overlaps(), and calculateOffset() inline methods.

 

The RouteTarget enumeration has three values: None (unmapped), SafeMemory (RAM), and MMIOManager (memory-mapped I/O devices). During initialization, initDefaultPARoutes() reads the memory map from EmulatorSettings and builds exactly two routes. Overlap validation runs at initialization and logs errors for any overlapping ranges.

 

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15.3.2 Default Route Configuration

 

 

With default settings, Route 1 spans [0x0, 0x880000000) covering 34 GB (ramBase 0x0 + 32 GB + low memory), and Route 2 spans [0x1000000000, 0x2000000000) covering 64 GB of Typhoon PCI I/O space. The setRoutes() method allows custom routing tables for non-standard configurations.

 

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15.3.3 SafeMemory Physical Address Layout

 

Because Route 1 uses identity mapping (offsetBase = 0), the SafeMemory offset equals the physical address for all RAM accesses. The layout within SafeMemory is:

 

PA 0x000000 - 0x1FFFFF SRM firmware (decompressed by SrmRomLoader)

   +-- 0x002000 HWRPB (Hardware Restart Parameter Block)

   +-- 0x008000 PAL entry (PC = 0x8001, PAL mode bit set)

   +-- 0x0xxxxx PAL vectors, SRM console code

PA 0x600000 PAL_BASE (dispatch table)

PA 0x900000 Decompressor staging area (temporary)

PA 0x80000000+ Main RAM (OS kernel, applications)

 

SRM firmware is decompressed into SafeMemory at PA 0x0 by SrmRomLoader during system initialization. There is no separate firmware region — after decompression, firmware is simply bytes in RAM.

 

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15.3.4 Platform Address Maps

 

The PlatformAddressMap structure in memory_core.h defines platform-specific physical address space layouts for different Alpha chipset families. Each map specifies RAM base, maximum and actual RAM size, MMIO base and size, and a vector of named Aperture structures for detailed per-hose MMIO sub-regions.

 

 

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15.3.5 Code Example – PA Routing Path

 

MEM_STATUS GuestMemory::readRouted(quint64 pa, quint8 width,

                                    quint64& outValue,

                                    AccessKind kind) const noexcept

{

    const PARouteEntry* route = findRoute(pa);

    if (!route) return MEM_STATUS::AccessViolation;

 

    const quint64 offset = route->calculateOffset(pa);

    switch (route->target) {

        case RouteTarget::SafeMemory:

            return m_safeMem->load(offset, width, outValue);

        case RouteTarget::MMIOManager:

            return m_mmio->handleRead(pa, width, outValue);

    }

}

 

See Also: memoryLib/memory_core.h (~412 lines) – PlatformAddressMap, Aperture, MEM_STATUS, SystemType_EmulatR; memoryLib/SrmRomLoader.h (~161 lines) – SRM firmware decompression-via-execution; configLib/global_EmulatorSettings.h – Memory map configuration.