What does Cortex m0+ access at 0xFFFF_FFF0-C addresses?

The Cortex-M0+ is a low-power microcontroller designed by ARM Holdings. It is commonly used in embedded systems and Internet of Things (IoT) devices. One of the key features of the Cortex-M0+ is its ability to access memory at specific addresses. In this article, we will explore what the Cortex-M0+ accesses at addresses in the range of 0xFFFF_FFF0 to 0xFFFF_FFFF.

Before we dive into the specific addresses, let's first understand a bit about memory in microcontrollers. Microcontrollers have different types of memory, including Flash memory, RAM, and registers. Flash memory is where the program code is stored, RAM is used for data storage during program execution, and registers are small storage units within the microcontroller.

Now, let's focus on the addresses in the range of 0xFFFF_FFF0 to 0xFFFF_FFFF. These addresses are part of the Cortex-M0+'s memory map. In this range, the Cortex-M0+ accesses a special type of memory called the System Control Space (SCS) or System Control Block (SCB).

The SCB is a crucial component of the Cortex-M0+ and is responsible for various system-level functions. It contains registers that control the behavior and configuration of the microcontroller. Let's take a look at some of the important registers in the SCB that the Cortex-M0+ accesses at these addresses:

1. CPUID (0xE000_ED00)

The CPUID register provides information about the microcontroller's CPU core. It contains fields that indicate the processor architecture, part number, revision, and other details. This register is read-only and cannot be modified by the user.

2. ICSR (0xE000_ED04)

The ICSR (Interrupt Control and State Register) is used to control and monitor the interrupt behavior of the Cortex-M0+. It contains fields that indicate the active interrupt number, the pending interrupt flag, and the interrupt priority levels. This register is both readable and writable.

3. VTOR (0xE000_ED08)

The VTOR (Vector Table Offset Register) is used to set the base address of the vector table. The vector table contains the addresses of interrupt service routines (ISRs) and exception handlers. By modifying the VTOR, the Cortex-M0+ can change the location of the vector table in memory. This register is both readable and writable.

4. AIRCR (0xE000_ED0C)

The AIRCR (Application Interrupt and Reset Control Register) is used to control the behavior of interrupts and resets. It contains fields that control the priority grouping, system reset, and debugging behavior. This register is both readable and writable.

5. SCR (0xE000_ED10)

The SCR (System Control Register) is used to configure various system-level options. It contains fields that control the sleep behavior, the use of the floating-point unit (if available), and the default exception handling. This register is both readable and writable.

6. CCR (0xE000_ED14)

The CCR (Configuration and Control Register) is used to configure various processor options. It contains fields that control the stack alignment, the use of unaligned memory access, and the division behavior. This register is both readable and writable.

These are just a few examples of the registers that the Cortex-M0+ accesses at addresses in the range of 0xFFFF_FFF0 to 0xFFFF_FFFF. Each register serves a specific purpose and allows the user to configure and control different aspects of the microcontroller's behavior.

It's important to note that directly accessing these registers without proper knowledge and understanding can lead to unintended consequences and system instability. It is recommended to consult the microcontroller's datasheet and reference manual for detailed information on each register and its usage.

In conclusion, the Cortex-M0+ accesses important system control registers in the range of 0xFFFF_FFF0 to 0xFFFF_FFFF. These registers allow the user to configure and control various aspects of the microcontroller's behavior. Understanding these registers and their purpose is essential for effectively utilizing the capabilities of the Cortex-M0+ microcontroller.