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This page provides detailed information about the OVP Fast Processor Model of the ARM arm926 (ARM926EJ-S) core.
This page is information about the arm926 alias of the ARM926EJ-S variant.
Processor IP owner is ARM Holdings.
OVP Fast Processor Model is written in C.
Provides a C API for use in C based platforms.
Provides a native C++ interface for use in SystemC TLM2 platforms.
The model is written using the OVP VMI API that provides a Virtual Machine Interface that defines the behavior of the processor.
The VMI API makes a clear line between model and simulator allowing very good optimization and world class high speed performance.
The model is provided as a binary shared object and is also available as source (different models have different licensing conditions). This allows the download and use of the model binary or the use of the source to explore and modify the model.
The model has been run through an extensive QA and regression testing process.
Traditionally, processor models and simulators make use of one thread on the host PC. Imperas have developed a technology, called QuantumLeap, that makes use of the many host cores found in modern PC/workstations to achieve industry leading simulation performance. To find out about the Imperas parallel simulation lookup Imperas QuantumLeap. There are videos of QuantumLeap on ARM here, and MIPS here. For press information related to QuantumLeap for ARM click here or for MIPS click here. Many of the OVP Fast Processor Models have been qualified to work with QuantumLeap - this is indicated for this model below.
This model executes instructions of the target architecture and provides an interface for debug access. An interface to GDB is provided and this allows the connection of many industry standard debuggers that use the GDB/RSP interface. For more information watch the OVP video here.
The model also works with the Imperas Multicore Debugger and advanced Verification, Analysis and Profiling tools.
An ISS is a software development tool that takes in instructions for a target processor and executes them. The heart of an ISS is the model of the processor. Imperas has developed a range of ISS products for use in embedded software development that utilize this fast Fast Processor Model. The Imperas ARM arm926 (ARM926EJ-S) ISS runs on Windows/Linux x86 systems and takes a cross compiled elf file of your program and allows very fast execution. The ARM arm926 (ARM926EJ-S) ISS also provides access to standard GDB/RSP debuggers and connects to the Eclipse IDE and Imperas debuggers.
Model downloadable (needs registration and to be logged in) in package arm.model for Windows32 and for Linux32. Note that the Model is also available for 64 bit hosts as part of the commercial products from Imperas.
Model Variant name: arm926 (ARM926EJ-S)
ARM Processor Model
Usage of binary model under license governing simulator usage.
Note that for models of ARM CPUs the license includes the following terms:
Licensee is granted a non-exclusive, worldwide, non-transferable, revocable licence to:
If no source is being provided to the Licensee: use and copy only (no modifications rights are granted) the model for the sole purpose of designing, developing, analyzing, debugging, testing, verifying, validating and optimizing software which: (a) (i) is for ARM based systems; and (ii) does not incorporate the ARM Models or any part thereof; and (b) such ARM Models may not be used to emulate an ARM based system to run application software in a production or live environment.
If source code is being provided to the Licensee: use, copy and modify the model for the sole purpose of designing, developing, analyzing, debugging, testing, verifying, validating and optimizing software which: (a) (i) is for ARM based systems; and (ii) does not incorporate the ARM Models or any part thereof; and (b) such ARM Models may not be used to emulate an ARM based system to run application software in a production or live environment.
In the case of any Licensee who is either or both an academic or educational institution the purposes shall be limited to internal use.
Except to the extent that such activity is permitted by applicable law, Licensee shall not reverse engineer, decompile, or disassemble this model. If this model was provided to Licensee in Europe, Licensee shall not reverse engineer, decompile or disassemble the Model for the purposes of error correction.
The License agreement does not entitle Licensee to manufacture in silicon any product based on this model.
The License agreement does not entitle Licensee to use this model for evaluating the validity of any ARM patent.
Source of model available under separate Imperas Software License Agreement.
Instruction pipelines are not modeled in any way. All instructions are assumed to complete immediately. This means that instruction barrier instructions (e.g. ISB, CP15ISB) are treated as NOPs, with the exception of any undefined instruction behavior, which is modeled. The model does not implement speculative fetch behavior. The branch cache is not modeled.
Caches and write buffers are not modeled in any way. All loads, fetches and stores complete immediately and in order, and are fully synchronous (as if the memory was of Strongly Ordered or Device-nGnRnE type). Data barrier instructions (e.g. DSB, CP15DSB) are treated as NOPs, with the exception of any undefined instruction behavior, which is modeled. Cache manipulation instructions are implemented as NOPs, with the exception of any undefined instruction behavior, which is modeled.
Real-world timing effects are not modeled: all instructions are assumed to complete in a single cycle.
TLBs are architecturally-accurate but not device accurate. This means that all TLB maintenance and address translation operations are fully implemented but the cache is larger than in the real device.
Models have been extensively tested by Imperas. ARM9 models have been successfully used by customers to simulate Linux and Nucleus on ArmIntegrator virtual platforms.
Thumb instructions are supported.
Trivial Jazelle extension is implemented.
FCSE extension is implemented.
VMSA address translation is implemented.
TLB behavior is controlled by parameter ASIDCacheSize. If this parameter is 0, then an unlimited number of TLB entries will be maintained concurrently. If this parameter is non-zero, then only TLB entries for up to ASIDCacheSize different ASIDs will be maintained concurrently initially; as new ASIDs are used, TLB entries for less-recently used ASIDs are deleted, which improves model performance in some cases (especially when 16-bit ASIDs are in use). If the model detects that the TLB entry cache is too small (entry ejections are very frequent), it will increase the cache size automatically. In this variant, ASIDCacheSize is 8
1 ITCM is implemented.
1 DTCM is implemented.
It is possible to enable model debug features in various categories. This can be done statically using the "override_debugMask" parameter, or dynamically using the "debugflags" command. Enabled debug features are specified using a bitmask value, as follows:
Value 0x004: enable debugging of MMU/MPU mappings.
Value 0x080: enable debugging of all system register accesses.
Value 0x100: enable debugging of all traps of system register accesses.
Value 0x200: enable verbose debugging of other miscellaneous behavior (for example, the reason why a particular instruction is undefined).
Value 0x800: enable dynamic validation of TLB entries against in-memory page table contents (finds some classes of error where page table entries are updated without a subsequent flush of affected TLB entries).
All other bits in the debug bitmask are reserved and must not be set to non-zero values.
AArch32 Unpredictable Behavior:
Many AArch32 instruction behaviors are described in the ARM ARM as CONSTRAINED UNPREDICTABLE. This section describes how such situations are handled by this model.
Equal Target Registers:
Some instructions allow the specification of two target registers (for example, double-width SMULL, or some VMOV variants), and such instructions are CONSTRAINED UNPREDICTABLE if the same target register is specified in both positions. In this model, such instructions are treated as UNDEFINED.
Floating Point Load/Store Multiple Lists:
Instructions that load or store a list of floating point registers (e.g. VSTM, VLDM, VPUSH, VPOP) are CONSTRAINED UNPREDICTABLE if either the uppermost register in the specified range is greater than 32 or (for 64-bit registers) if more than 16 registers are specified. In this model, such instructions are treated as UNDEFINED.
Floating Point VLD[2-4]/VST[2-4] Range Overflow:
Instructions that load or store a fixed number of floating point registers (e.g. VST2, VLD2) are CONSTRAINED UNPREDICTABLE if the upper register bound exceeds the number of implemented floating point registers. In this model, these instructions load and store using modulo 32 indexing (consistent with AArch64 instructions with similar behavior).
If-Then (IT) Block Constraints:
Where the behavior of an instruction in an if-then (IT) block is described as CONSTRAINED UNPREDICTABLE, this model treats that instruction as UNDEFINED.
Use of R13:
In architecture variants before ARMv8, use of R13 was described as CONSTRAINED UNPREDICTABLE in many circumstances. From ARMv8, most of these situations are no longer considered unpredictable. This model allows R13 to be used like any other GPR, consistent with the ARMv8 specification.
Use of R15:
Use of R15 is described as CONSTRAINED UNPREDICTABLE in many circumstances. This model allows such use to be configured using the parameter "unpredictableR15" as follows:
Value "undefined": any reference to R15 in such a situation is treated as UNDEFINED;
Value "nop": any reference to R15 in such a situation causes the instruction to be treated as a NOP;
Value "raz_wi": any reference to R15 in such a situation causes the instruction to be treated as a RAZ/WI (that is, R15 is read as zero and write-ignored);
Value "execute": any reference to R15 in such a situation is executed using the current value of R15 on read, and writes to R15 are allowed (but are not interworking).
Value "assert": any reference to R15 in such a situation causes the simulation to halt with an assertion message (allowing any such unpredictable uses to be easily identified).
In this variant, the default value of "unpredictableR15" is "execute".
Unpredictable Instructions in Some Modes:
Some instructions are described as CONSTRAINED UNPREDICTABLE in some modes only (for example, MSR accessing SPSR is CONSTRAINED UNPREDICTABLE in User and System modes). This model allows such use to be configured using the parameter "unpredictableModal", which can have values "undefined" or "nop". See the previous section for more information about the meaning of these values.
In this variant, the default value of "unpredictableModal" is "nop".
This model implements a number of non-architectural pseudo-registers and other features to facilitate integration.
Memory Transaction Query:
Two registers are intended for use within memory callback functions to provide additional information about the current memory access. Register transactPL indicates the processor execution level of the current access (0-3). Note that for load/store translate instructions (e.g. LDRT, STRT) the reported execution level will be 0, indicating an EL0 access. Register transactAT indicates the type of memory access: 0 for a normal read or write; and 1 for a physical access resulting from a page table walk.
Page Table Walk Query:
A banked set of registers provides information about the most recently completed page table walk. There are up to six banks of registers: bank 0 is for stage 1 walks, bank 1 is for stage 2 walks, and banks 2-5 are for stage 2 walks initiated by stage 1 level 0-3 entry lookups, respectively. Banks 1-5 are present only for processors with virtualization extensions. The currently active bank can be set using register PTWBankSelect. Register PTWBankValid is a bitmask indicating which banks contain valid data: for example, the value 0xb indicates that banks 0, 1 and 3 contain valid data.
Within each bank, there are registers that record addresses and values read during that page table walk. Register PTWBase records the table base address, register PTWInput contains the input address that starts a walk, register PTWOutput contains the result address and register PTWPgSize contains the page size (PTWOutput and PTWPgSize are valid only if the page table walk completes). Registers PTWAddressL0-PTWAddressL3 record the addresses of level 0 to level 3 entries read, respectively. Register PTWAddressValid is a bitmask indicating which address registers contain valid data: bits 0-3 indicate PTWAddressL0-PTWAddressL3, respectively, bit 4 indicates PTWBase, bit 5 indicates PTWInput, bit 6 indicates both PTWOutput and PTWPgSize. For example, the value 0x73 indicates that PTWBase, PTWInput, PTWOutput, PTWPgSize and PTWAddressL0-L1 are valid but PTWAddressL2-L3 are not. Register PTWAddressNS is a bitmask indicating whether an address is in non-secure memory: bits 0-3 indicate PTWAddressL0-PTWAddressL3, respectively, bit 4 indicates PTWBase, bit 6 indicates PTWOutput (PTWInput is a VA and thus has no secure/non-secure info). Registers PTWValueL0-PTWValueL3 contain page table entry values read at level 0 to level 3. Register PTWValueValid is a bitmask indicating which value registers contain valid data: bits 0-3 indicate PTWValueL0-PTWValueL3, respectively.
Artifact Page Table Walks:
Registers are also available to enable a simulation environment to initiate an artifact page table walk (for example, to determine the ultimate PA corresponding to a given VA). Register PTWI_EL1S initiates a secure EL1 table walk for a fetch. Register PTWD_EL1S initiates a secure EL1 table walk for a load or store (note that current ARM processors have unified TLBs, so these registers are synonymous). Registers PTW[ID]_EL1NS initiate walks for non-secure EL1 accesses. Registers PTW[ID]_EL2 initiate EL2 walks. Registers PTW[ID]_S2 initiate stage 2 walks. Registers PTW[ID]_EL3 initiate AArch64 EL3 walks. Finally, registers PTW[ID]_current initiate current-mode walks (useful in a memory callback context). Each walk fills the query registers described above.
MMU and Page Table Walk Events:
Two events are available that allow a simulation environment to be notified on MMU and page table walk actions. Event mmuEnable triggers when any MMU is enabled or disabled. Event pageTableWalk triggers on completion of any page table walk (including artifact walks).
Artifact Address Translations:
A simulation environment can trigger an artifact address translation operation by writing to the architectural address translation registers (e.g. ATS1CPR). The results of such translations are written to an integration support register artifactPAR, instead of the architectural PAR register. This means that such artifact writes will not perturb architectural state.
A simulation environment can cause TLB state for one or more address translation regimes in the processor to be flushed by writing to the artifact register ResetTLBs. The argument is a bitmask value, in which non-zero bits select the TLBs to be flushed, as follows:
Bit 1: EL0/EL1 stage 1 non-secure TLB
Halt Reason Introspection:
An artifact register HaltReason can be read to determine the reason or reasons that a processor is halted. This register is a bitfield, with the following encoding: bit 0 indicates the processor has executed a wait-for-event (WFE) instruction; bit 1 indicates the processor has executed a wait-for-interrupt (WFI) instruction; and bit 2 indicates the processor is held in reset.
System Register Access Monitor:
If parameter "enableSystemMonitorBus" is True, an artifact 32-bit bus "SystemMonitor" is enabled for each PE. Every system register read or write by that PE is then visible as a read or write on this artifact bus, and can therefore be monitored using callbacks installed in the client environment (use opBusReadMonitorAdd/opBusWriteMonitorAdd or icmAddBusReadCallback/icmAddBusWriteCallback, depending on the client API). The format of the address on the bus is as follows:
bits 31:26 - zero
bit 25 - 1 if AArch64 access, 0 if AArch32 access
bit 24 - 1 if non-secure access, 0 if secure access
bits 23:20 - CRm value
bits 19:16 - CRn value
bits 15:12 - op2 value
bits 11:8 - op1 value
bits 7:4 - op0 value (AArch64) or coprocessor number (AArch32)
bits 3:0 - zero
As an example, to view non-secure writes to writes to CNTFRQ_EL0 in AArch64 state, install a write monitor on address range 0x020e0330:0x020e0333.
System Register Implementation:
If parameter "enableSystemBus" is True, an artifact 32-bit bus "System" is enabled for each PE. Slave callbacks installed on this bus can be used to implement modified system register behavior (use opBusSlaveNew or icmMapExternalMemory, depending on the client API). The format of the address on the bus is the same as for the system monitor bus, described above.
OVP simulator downloadable (needs registration and to be logged in) in package OVPsim for Windows32 and for Linux32. Note that the simulator is also available for 64 bit hosts as part of the commercial products from Imperas.
OVP Download page here.
OVP documentation that provides overview information on processor models is available OVP_Guide_To_Using_Processor_Models.pdf.
Full model specific documentation on the variant arm926 (ARM926EJ-S) is available OVP_Model_Specific_Information_arm_ARM926EJ-S.pdf.
Location: The Fast Processor Model source and object file is found in the installation VLNV tree: arm.ovpworld.org/processor/arm/1.0
Processor Endian-ness: This model can be set to either endian-ness (normally by a pin, or the ELF code).
Processor ELF Code: The ELF code for this model is: 0x28
QuantumLeap Support: The processor model is qualified to run in a QuantumLeap enabled simulator.
The arm926 OVP Fast Processor Model also has parameters, model commands, and many registers.
The model may also have hierarchy or be multicore and have other attributes and capabilities.
To see this information, please have a look at the model variant specific documents.
Click here to see the detailed document OVP_Model_Specific_Information_arm_ARM926EJ-S.pdf.
Information on the arm926 OVP Fast Processor Model can also be found on other web sites::
www.ovpworld.org has the library pages http://www.ovpworld.org/library/wikka.php?wakka=CategoryProcessor
www.imperas.com has more information on the model library
http://www.ovpworld.org: VMI Operating System support (VMI OS) API Reference Guide
http://www.ovpworld.org: Control File User Guide
Currently available Fast Processor Model Families.