板载系统存储器
物理存储器GVD241PCB提供同步DRAM（SDRAM）作为板载系统存储器。内存可以作为字节、字或长字访问。GVD241PCB接受一个144针SDRAM SODIMM，最大容量为512 MB。板载DRAM通过PCI到VME桥接器双端口连接到VME总线，可由本地处理器寻址，也可由另一个VMEbus主机寻址VMEbuss从机接口。在本地处理器和VME总线之间共享内存时，必须小心，以防止VME总线主机覆盖本地处理器的操作系统。注：在Windows NT 4.0中使用VMIC的IOWorks Access的配置实用程序配置RAM时，请不要请求超过25%的物理RAM。超过25%的限制可能会导致已知的Windows NT错误，在Windows NT启动过程中会导致不可预测的行为，并且需要使用紧急修复磁盘来恢复计算机。此错误存在于Windows NT 4.0 service pack级别3中。建议将紧急修复磁盘保持为最新且易于访问
内存映射
内存映射-基于Tundra Universe II的PCI到VMEbus桥基于Tunda Universe III的接口GVD241PCB的内存映射如表2-1所示。所有系统都共享相同的内存映射，尽管VMIVME7750的SDRAM不足256 MB，无法填充为板载扩展内存保留的全部空间。表2-1 GVD241PCB，基于Universe II的接口内存地址映射模式内存地址范围大小描述受保护模式$FFFF 0000-$FFFFFF 64 KB ROM BIOS映像$0400 0000-$FFFE FFFF 3.9 GB未使用*$0010 0000-$0FFF FFFF 255 MB保留给**板载扩展内存（未在所有系统上填充）REAL模式$E0000-$FFFFF 128 KB ROM BIOS$D8018-$DFFFF 32 KB保留$D8016-$D8017 2字节板ID寄存器（0x7750）$D8014-$D8015 2字节VMEBERR地址修改器寄存器$D8010-$D8013 2字节MEBERR地址寄存器$D800E-$D800F 2字节系统通信寄存器$D8000-$D800D 14字节保留$C8000-$D7FFF 64 KB LANWorks BIOS$C0000-$C7FFF 32 KB视频ROM$A0000-$BFFFF 128 KB视频RAM$00000-$9FFF 640 KB用户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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