ARM
ARM (Advanced RISC Machines) is a family of RISC instruction set architectures (ISAs) for computer processors.
ARM assembly branching example:
ARM Versions
ARMv7
ARMv7 is von Neumman architecture.
ARMv7 has three stages: fetch, decode, and execute.
ARMv8
Raspberry Pi 4.
ARMv9
ARMv9 uses Harvard architecture.
ARM Cortex-A
Application processor cores for a performance-intensive systems.
- iMX.8 - Cortex-A (mainly) for automotive applications
- BCM2711 - Broadcom chip used in Raspberry Pi 4 model B. Quad-core Cortex-A72 (ARM v8) 64-bit SoC @ 1.5 GHz.
ARM Cortex-M
Microcontroller cores for a wide range of embedded applications. Usually, they don’t have MMU (memory management unit).
ARM Cortex-R
High-performance cores for real-time applications.
ARM Execution Levels
The processor can be executing in different modes of operation, therefore different registers are available.
ARM Execution Levels:
- EL0 - User applications
- EL1 - OS kernel (supervisor)
- EL2 - Hypervisor
- EL3 - Secure monitor
ARM Exceptions
Four types of exceptions:
- Software
- Hardware
- Fast
- Exceptions