Author: System on Chips

Virtual Interrupt Handling in GICv3: EOI Split Mode and Hypervisor Behavior The ARM Generic Interrupt Controller (GIC) version 3 introduces advanced virtualization support, enabling efficient handling of virtual interrupts in hypervisor environments. A key feature of GICv3 is the End-of-Interrupt (EOI) split mode, which separates the priority drop and interrupt deactivation operations. This separation is…

ARM Cortex-M23 MPU Configuration Leading to Hard Fault The issue at hand involves a hard fault occurring immediately after enabling the Memory Protection Unit (MPU) on an ARM Cortex-M23 processor, specifically on the SAML11 board. The MPU is a critical component for enforcing memory access rules, and its misconfiguration can lead to severe system instability,…

ARMv8-A Stack Pointer Management: SP_EL1 Access Restrictions at EL1 In the ARMv8-A architecture, managing stack pointers (SP) across different exception levels (ELs) is a critical aspect of system software design. One of the key points of confusion arises when dealing with the stack pointer registers at EL1, specifically the distinction between directly accessing SP_EL1 and…

MPU Region Size Halving and Memory Management Faults in Cortex-M4 The ARM Cortex-M4 Memory Protection Unit (MPU) is a critical component for ensuring memory safety and access control in embedded systems. However, improper configuration of the MPU can lead to unexpected behavior, such as memory management faults or incorrect region sizing. In this case, the…

EL1 Software Access to S2 Translation Table Base (TTB) in SMMU Stream Table Entry The ARM System Memory Management Unit (SMMU) is a critical component in modern ARM-based systems, enabling virtualization and memory isolation for devices. A key feature of the SMMU is its support for two-stage address translation, where Stage 1 (S1) handles virtual-to-physical…

Cortex-A78 Multicore Bare Metal Startup Challenges When working with the Cortex-A78, a high-performance multicore processor, one of the most critical tasks is developing bare metal startup code. This code is responsible for initializing the hardware, setting up the memory system, and transitioning control to the application. The Cortex-A78, being part of the ARMv8.2-A architecture, introduces…

ARM Cortex-A53 SVC Execution at EL1: Correct vs. Incorrect Exception Syndrome In ARMv8 architectures, the SVC (Supervisor Call) instruction is a critical mechanism for invoking privileged operations from lower exception levels. When executed at EL1 (Exception Level 1), the SVC instruction should generate a synchronous exception with a specific exception class (EC) in the ESR_EL1…

ARM Cortex-M7 Prefetch Unit and Instruction Fetch Efficiency The ARM Cortex-M7 processor, known for its high performance and efficiency, incorporates several advanced features to optimize instruction execution. One such feature is the Prefetch Unit (PFU), which plays a critical role in fetching instructions from memory and feeding them into the processor’s pipeline. The PFU is…

ARM Cortex-M4 Recursive Fibonacci Code Fails to Terminate The core issue revolves around a recursive implementation of the Fibonacci sequence on an ARM Cortex-M4 processor, where the code fails to terminate after computing the first four Fibonacci numbers. Instead, it enters an infinite loop, continuously branching back to the recursive subroutine. The goal is to…

Cortex-M0+ MPU Access Violation During SVC Handler Execution The Cortex-M0+ processor, while being a lightweight and efficient ARM core, presents unique challenges when combining the Memory Protection Unit (MPU) with Supervisor Call (SVC) instructions. A common issue arises when transitioning between privileged and unprivileged modes, particularly when the MPU is configured to restrict access to…