Application Processors Part 2 Flashcards
What are the ARMv7 Cortex-A series features?
- Thumb and Jazelle
- Vector floating point architecture
- Single instruction multiple data
- big.Little System
- Dynamic voltage and frequency scaling
- TrustZone
What are the two instruction sets?
- ARM : standard 32-bit instruction set
- Thumb : 16-bit compressed form
What are the important features of THUMB mode?
- Only low registers r0 to r7 are fully accessible
- Only branch instruction can be conditionally executed
- Barrel shift operations are separate instructions
What is the interworking of Thumb?
- To call a thumb routine from an ARM routine the core has to change state : T bit in CPSR
- BX and BLX instruction can be used for the switch.
What is Jazelle?
Since Java byte code is executed in hardware, the Java byte code is the result of the compilation of a Java program. Recognized Java byte codes are converted into a string of one or more native ARM instructions
What is Vector Floating Point (VFP)
?It is a coprocessor
- CPD() cp, opcode1, Cd, Cn, Cm
– Cp represents coprocessor number between p0 to p15
– Opcode field describes coprocessor operation
– Cd, Cn, Cm coprocessor registers
Coprocessor register transfer and memory transfer instructions are distinct from the main ARM processor
What is VFP registers?
32 bit wide VFP register file organized as four register banks, each including 8 registers.
- The first bank is used to hold scalar operands whereas the remaining three banks vector operands
What is VFP operation
- A vector operand may refer to 2 to 8 registers from the same bank
- The vector length is given in a specific field of a control register
- The register numbers given in the instruction specify the first registers that contain the first operands and specify the first destination register
- Each successive element of the vector is taken by incrementing appropriately the register numbers
What is SIMD?
Single instruction multiple data.
Single instruction operates on multiple data elements
What is parallelism in SIMD processing?
- Signal instruction operates on multiple data elements
- Multiple processing elements
- Time-space duality
What is the time space duality?
Array processor: Instruction operates on multiple data elements at the same time
Vector processor: Instruction operates on multiple data elements in consecutive time steps
What is big.Little processing?
- Aims primary at power reduction
- Workload of smartphones and tablets is dynamically changing
- High intensity tasks: Games, Video
- Low intensity tasks: Audio, email, news paper
Advantage of big.Little processing?
- Uses the right processor for the right job
- Up to 70% energy savings on common workloads
- Flexible and transparent to apps
What are the three clusters of big.Little?
- 2.5GHz eXtreme performance
- 2.0GHz bestperf/power balance
- 1.4GHz Best Power Efficiency
What is DVFS?
Dynamic Voltage and Frequency Scaling
- Since energy is proportional to f^2, DVFS can potentially provide significant energy savings through frequency and voltage scaling
