EMB426 Windows CE Memory Architecture.pptVIP

Mobile Embedded DevCon 2005 EMB426Windows CE Memory Architecture Steve Maillet CEO/Chief Software Architect EmbeddedFusion Part IArchitecture and concepts Virtual Memory Kernel Mode versus User Mode Statically mapped memory Process memory System API Calls Access Permissions Virtual Memory Model Single 32-bit (4 Gigabyte) flat virtual memory address space Permits efficient use of physical memory with protection Virtual addresses translated to physical addresses by MMU A valid virtual address maps to a physical address Static or Dynamically mapped virtual addressing Virtual Memory Kernel Mode Versus User Mode ONLY Difference is access to different regions Kernel mode code has full access to all memory Process protection still applies! User Mode code only has access to User Space Kernel Space (0– 0xFFFFFFFF) Used only by Kernel-mode code with privileged access (“Kmode”) SetKMode() protected API or ROMFLAGS Setting for ALL threads in the system User Space (0– 0x7FFFFFFF) Organized as 64 slots of 32 MB (225 bytes) each Applications, DLLs and Data located here Statically Mapped Memory Statically Mapped Memory x86, ARM OEM provides OEMAddressTable in OAL to define initial mappings MIPS, SHx Mapping is fixed in the MMU architecture Process Memory System API Calls System API Calls Coredll.dll Located at the top of every process slot Fields system API calls from user mode threads Implements some system API calls directly Causes an exception (trap) to pass on system API request Kernel Catches system API request exception traps Dispatches to a system EXE to fulfill request User mode thread migrated to system EXE process space Access rights of user mode thread inherits current process rights System API Calling Mechanism Access Permissions Process Access Permissions Access permissions set on per-thread basis GetProcPermissions() / SetProcPermissions() Threads accessing other process slots require permission Violations cause exceptions reported to the Kern