板載系統(tǒng)存儲器
物理存儲器GVD241PCB提供同步DRAM（SDRAM）作為板載系統(tǒng)存儲器。內(nèi)存可以作為字節(jié)、字或長字訪問。GVD241PCB接受一個144針SDRAM SODIMM，最大容量為512 MB。板載DRAM通過PCI到VME橋接器雙端口連接到VME總線，可由本地處理器尋址，也可由另一個VMEbus主機尋址VMEbuss從機接口。在本地處理器和VME總線之間共享內(nèi)存時，必須小心，以防止VME總線主機覆蓋本地處理器的操作系統(tǒng)。注：在Windows NT 4.0中使用VMIC的IOWorks Access的配置實用程序配置RAM時，請不要請求超過25%的物理RAM。超過25%的限制可能會導(dǎo)致已知的Windows NT錯誤，在Windows NT啟動過程中會導(dǎo)致不可預(yù)測的行為，并且需要使用緊急修復(fù)磁盤來恢復(fù)計算機。此錯誤存在于Windows NT 4.0 service pack級別3中。建議將緊急修復(fù)磁盤保持為最新且易于訪問
內(nèi)存映射
內(nèi)存映射-基于Tundra Universe II的PCI到VMEbus橋基于Tunda Universe III的接口GVD241PCB的內(nèi)存映射如表2-1所示。所有系統(tǒng)都共享相同的內(nèi)存映射，盡管VMIVME7750的SDRAM不足256 MB，無法填充為板載擴展內(nèi)存保留的全部空間。表2-1 GVD241PCB，基于Universe II的接口內(nèi)存地址映射模式內(nèi)存地址范圍大小描述受保護模式$FFFF 0000-$FFFFFF 64 KB ROM BIOS映像$0400 0000-$FFFE FFFF 3.9 GB未使用*$0010 0000-$0FFF FFFF 255 MB保留給**板載擴展內(nèi)存（未在所有系統(tǒng)上填充）REAL模式$E0000-$FFFFF 128 KB ROM BIOS$D8018-$DFFFF 32 KB保留$D8016-$D8017 2字節(jié)板ID寄存器（0x7750）$D8014-$D8015 2字節(jié)VMEBERR地址修改器寄存器$D8010-$D8013 2字節(jié)MEBERR地址寄存器$D800E-$D800F 2字節(jié)系統(tǒng)通信寄存器$D8000-$D800D 14字節(jié)保留$C8000-$D7FFF 64 KB LANWorks BIOS$C0000-$C7FFF 32 KB視頻ROM$A0000-$BFFFF 128 KB視頻RAM$00000-$9FFF 640 KB用戶RAM/DOS RAM
Onboard system memory
The physical memory GVD241 PCB provides synchronous DRAM (SDRAM) as on-board system memory. Memory can be accessed as bytes, words, or long words. The GVD241PCB accepts a 144 pin SDRAM SODIMM with a maximum capacity of 512 MB. The onboard DRAM is connected to the VME bus through the dual ports of PCI to VME bridge, and can be addressed by the local processor, or another VMEbus host can address the VMEbus slave interface. When sharing memory between the local processor and VME bus, care must be taken to prevent the VME bus host from overwriting the operating system of the local processor. Note: When using the configuration utility of VMIC IOWorks Access to configure RAM in Windows NT 4.0, do not request more than 25% of physical RAM. Exceeding the 25% limit may result in known Windows NT errors, unpredictable behavior during Windows NT startup, and the use of emergency repair disks to recover your computer. This error exists in Windows NT 4.0 service pack level 3. It is recommended that the Emergency Repair Disk be kept up to date and easily accessible
Memory Mapping
Memory mapping - The memory mapping from Tundra Universe II based PCI to VMEbus bridge based interface GVD241PCB of Tunda Universe III is shown in Table 2-1. All systems share the same memory mapping, although the SDRAM of the VMIVME7750 is less than 256 MB, and it cannot fill all the space reserved for the onboard extended memory. Table 2-1 GVD241PCB, Universal II based interface memory address mapping mode memory address range size description protected mode $FFFF 0000 - $FFFFFF 64 KB ROM BIOS image $0400 0000 - $FFFE FFFF 3.9 GB unused * $0010 0000 - $0FFF FFFF 255 MB reserved for * * on-board extended memory (not populated on all systems) REAL mode $E0000 - $FFFFF 128 KB ROM BIOS $D8018 - $DFFFF 32 KB reserved $D8016 - $D8017 2-byte board ID register (0x7750) $D8014 - $D8015 2-byte VMEBERR address modifier register $D8010 - $D8013 2-byte MEBERR address register $D800E - $D800F 2-byte system communication register $D8000 - $D800D 14 byte reserved $C8000 - $D7FFF 64 KB LANWorks BIOS $C0000 - $C7FFF 32 KB video ROM $A0000 - $BFFFF 128 KB video RAM $00000 - $9FFF 640 KB user RAM/DOS RAM
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