Architectures and Processors

Non-Secure HardFault Handler Trapping and EXC_RETURN Value Analysis When dealing with ARM Cortex-M processors that implement the ARMv8-M architecture, one of the critical aspects of debugging and fault handling is understanding the behavior of the EXC_RETURN value, especially in the context of secure and non-secure states. The EXC_RETURN value is a special code that the…

ARM Cortex-M0+ C Variable Access in Assembly Code When working with ARM Cortex-M0+ processors, one common task is accessing C variables from assembly code. This is particularly important in embedded systems where low-level hardware control and performance optimizations are required. The process involves understanding how global variables defined in C can be referenced and manipulated…

ARM Cortex-M4 Startup Failure and Memory Corruption During __libc_init_array Execution The issue described revolves around a memory-related runtime error occurring during the startup sequence of an STM32L476VGT microcontroller, specifically during the execution of the __libc_init_array function. This function is part of the C runtime initialization and is responsible for calling static constructors and initialization functions….

Volatile Variable Stack Allocation and Overwrite During Mixed C-ASM Execution When working with mixed C and assembly code on ARM Cortex-M3 processors, a common issue arises when volatile variables are allocated on the stack and subsequently overwritten during function calls. This problem is particularly pronounced when the assembly function modifies the stack by pushing additional…

ARM Cortex-M4 Audio Mixing Performance with SD Card and I2S DMA The ARM Cortex-M4 processor, particularly in the STM32F429IGT6 microcontroller, is a popular choice for embedded audio applications due to its balance of performance, power efficiency, and peripheral support. However, achieving efficient real-time multi-channel audio mixing with hard latency requirements (less than 50ms) presents several…

ARM SMMU and Linux Page Table Sharing: Non-Deterministic Behavior During FPGA Transfers The integration of the ARM System Memory Management Unit (SMMU) with Linux-generated page tables on an ARM Cortex-A53-based Xilinx Zynq Ultrascale+ board presents a complex challenge. The goal is to enable shared virtual addressing (SVA) between the Cortex-A53 CPUs and an FPGA, leveraging…

ARM Cortex-M7 HardFault Handler Behavior with BKPT Instruction The behavior of the ARM Cortex-M7 processor when encountering a BKPT instruction within a HardFault handler is a critical topic for embedded systems engineers. The BKPT instruction, short for "Breakpoint," is typically used for debugging purposes. However, its behavior changes significantly depending on whether a debugger is…

ARMv8 MMU Level 2 Table Invalid Entry Behavior with 64KB Granule In ARMv8 architectures, the Memory Management Unit (MMU) is responsible for translating virtual addresses (VA) to physical addresses (PA) using a multi-level page table structure. When using a 64KB granule size, the MMU employs a three-level page table hierarchy: Level 1, Level 2, and…

ARM Cortex-M33 TrustZone Context Switching Challenges The ARM Cortex-M33 processor, as used in the NXP LPC5500 series, introduces TrustZone technology for secure and non-secure state separation. When integrating FreeRTOS with TrustZone, a common challenge arises in transitioning between secure and non-secure tasks. The core issue manifests when attempting to switch from a secure FreeRTOS task…

Cortex-A5 Real-Time Task Execution and APB Access Latency Challenges The Cortex-A5 processor, as implemented in the SAMA5D27 microcontroller from Microchip, is a versatile and power-efficient core designed for a wide range of embedded applications. However, when tasked with real-time operations, particularly those requiring deterministic timing, certain architectural and configuration nuances can lead to performance bottlenecks….