ARM Processor Programming Modes - ARM Processor - Microcontroller and Embedded Programming

Summary

This video delves into the various operational modes of the ARM processor, which is commonly used in embedded systems due to its small size and programmability. The script covers seven modes of operation, which are categorized as privileged and non-privileged. It explains how these modes influence the access to registers and the Current Program Status Register (CPSR). The modes discussed include user mode, interrupt handling modes, supervisor mode, and system mode, each serving specific functions for handling different types of tasks and system processes. The video provides an overview of how these modes control the processor's behavior and access to resources.

Takeaways

• 😀 The ARM processor is a programmable processor used in embedded systems, known for its small size and versatility in various applications.
• 😀 The processor operates in different modes that control the availability of registers and the ability to access the Current Program Status Register (CPSR).
• 😀 There are two categories of operating modes: privileged modes (6 modes) and non-privileged mode (1 mode).
• 😀 Privileged modes provide full read and write access to the CPSR, while non-privileged modes only allow read access to the CPSR.
• 😀 The non-privileged mode is called **User Mode**, where most tasks are executed, but memory and hardware access is restricted.
• 😀 **Fast Interrupt Request (FIQ)** mode handles high-priority interrupts from fast peripherals and is a privileged mode with full CPSR access.
• 😀 **Interrupt Request (IRQ)** mode handles low-priority interrupts from peripherals like keyboards and is also a privileged mode with full CPSR access.
• 😀 **Supervisor Mode** provides additional privileges and greater control over the system, allowing tasks like I/O reading and OS kernel operations.
• 😀 **Undefined Mode** handles undefined instructions that the processor cannot recognize, while **Abort Mode** is entered when there is a failure in memory access.
• 😀 **System Mode** is a special privileged version of User Mode that provides full read and write access to CPSR, typically used in ARM processor version 4.
• 😀 Each mode's operation and control are determined by control bits in the CPSR, which define the mode selection based on specific bit configurations.

Q & A

What is the ARM processor, and how is it used?

The ARM processor is a programmable processor used in embedded systems. It allows programming through instructions that are written into its memory, making it suitable for specific applications in these systems.

What are the two main categories of ARM processor modes?

The two main categories of ARM processor modes are privileged modes and non-privileged modes.

What is the difference between privileged and non-privileged modes in ARM processors?

Privileged modes allow full read and write access to the Current Program Status Register (CPSR), while non-privileged modes only provide read access to the CPSR, specifically allowing control field reading.

What is the user mode in ARM processors?

User mode is a non-privileged mode where most tasks of the ARM processor are executed. In this mode, access to memory is restricted, and hardware devices cannot be read directly.

What does the Fast Interrupt Request (FIQ) mode handle in the ARM processor?

The Fast Interrupt Request (FIQ) mode handles high-priority interrupts generated by peripherals. It is a privileged mode that allows both reading and writing the CPSR.

What is the difference between the Fast Interrupt Request (FIQ) mode and the Interrupt Request (IRQ) mode?

FIQ mode handles high-priority interrupts, whereas IRQ mode handles low-priority interrupts. Both modes deal with interrupts generated by peripherals but at different priority levels.

What is supervisor mode, and what additional privileges does it provide?

Supervisor mode is a privileged mode that provides additional privileges and greater control over the system. It is used when the processor is at rest or when a software interrupt occurs. The mode is often used by operating system kernels and for accessing I/O modules.

When is the ARM processor in the abort mode?

The abort mode is entered when the processor attempts to access memory but fails to do so. This typically occurs when there is an issue with memory access.

What is the system mode in ARM processors, and how does it differ from user mode?

System mode is a privileged mode that is similar to user mode but with full read and write access to the CPSR. It is considered a special or higher version of user mode, providing more control over the processor.

How are ARM processor modes selected?

ARM processor modes are selected using mode selection bits in the CPSR. These bits (b4, b3, b2, b1, and b0) determine the processor mode, with specific bit patterns assigned to each mode such as user mode, FIQ, IRQ, and others.