Memory Protection and Properties
6-62
ADSP-BF535 Blackfin Processor Hardware Reference
A single instruction may generate an instruction fetch as well as one or
two data accesses. It is possible that more than one of these memory oper-
ations references data for which there is no valid CPLB descriptor in an
MMR pair. In this case, the exceptions are prioritized and serviced in this
order:
1. Instruction page miss
2. A miss on DAG0
3. A miss on DAG1
MMU Application
Memory management is an optional feature in the Blackfin architecture.
Its use is predicated on the system requirements of a given application.
Upon reset, all CPLBs are disabled, and the MMU is not used.
If all L1 Memory is configured as SRAM, then the data and instruction
MMU functions are optional, depending on the application’s need for
protection of memory spaces either between tasks or between User and
Supervisor modes. To protect memory between tasks, the operating sys-
tem can maintain separate tables of instruction and/or data memory pages
available for each task and make those pages visible only when the relevant
task is running. When a task switch occurs, the operating system can
ensure the invalidation of any CPLB descriptors on chip that should not
be available to the new task. It can also preload descriptors appropriate to
the new task.
For many operating systems, the application program is run in User mode
while the operating system and its services run in Supervisor mode. It is
desirable to protect code and data structures used by the operating system
from inadvertent modification by a running User mode application. This
protection can be achieved by defining CPLB descriptors for protected
memory ranges that allow write access only when in Supervisor mode. If a
write to a protected memory region is attempted while in User mode, an
Summary of Contents for ADSP-BF535 Blackfin
Page 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Page 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Page 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Page 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Page 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Page 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Page 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Page 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Page 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...