ARM Cortex-M Register Spilling Behavior Under -O0 Optimization When compiling C/C++ code for ARM Cortex-M processors using the -O0 optimization flag, developers often observe inconsistent behavior in how the compiler handles register spilling. Register spilling refers to the process of storing register contents into RAM (typically the stack) to free up registers for other operations….
Cortex-M55 LDRx Instruction Set Limitations The Cortex-M55, as part of the ARMv8-M architecture, introduces several enhancements over its predecessors, particularly in the areas of security and performance. However, one notable limitation is the absence of post-indexed and pre-indexed load instructions (LDR{type}{cond} Rt, [Rn], ±Rm {, shift} ; or LDR{type}{cond} Rt, [Rn, ±Rm {, shift}]!). These…
Master 1 Writes to SharedClean Cacheline: CleanUnique Transaction and State Transition In a system utilizing the ARM ACE (AXI Coherency Extensions) protocol, cache coherency is maintained across multiple cache masters connected via a coherent interconnect. Consider a scenario where two cache masters, Master 0 and Master 1, both hold a cacheline in the SharedClean (SC)…
ARM Cortex-M4 STR Instruction Execution Without Memory Update The core issue revolves around the STRGT instruction in an ARM Cortex-M4 assembly implementation of the Bubble Sort algorithm. The STRGT instruction is designed to conditionally store a register’s value into memory if the Greater Than (GT) condition is met. In this case, the instruction executes as…
SPI RXNE Flag Behavior and Stalling During Data Reception The STM32F407 microcontroller, based on the ARM Cortex-M4 architecture, is widely used in embedded systems for its robust peripheral support, including Serial Peripheral Interface (SPI) communication. However, a common issue arises when using the SPI peripheral for data transmission and reception, specifically related to the RXNE…
ARM Security Attribution Unit (IDAU/SAU) and Memory Protection Controller (MPC) Interaction The ARM architecture incorporates several components to manage memory security and access control, including the Implementation Defined Attribution Unit (IDAU), Security Attribution Unit (SAU), and Memory Protection Controller (MPC). These components work together to enforce security policies, but their roles and interactions can be…
ARM Cortex-A53 Cache Coherency Problems During Non-Coherent DMA Transfers The ARM Cortex-A53 processor, a widely used 64-bit ARMv8-A core, is designed with a hierarchical cache architecture, including L1 and L2 caches, to optimize memory access latency and bandwidth. However, when dealing with Direct Memory Access (DMA) transfers from non-coherent hardware masters, such as an FPGA…
Understanding the Transition from Handler Mode to Thread Mode in ARM Cortex-M Processors The ARM Cortex-M series of processors, including the Cortex-M3 and Cortex-M7, are widely used in embedded systems due to their efficiency, low power consumption, and real-time capabilities. One of the key architectural features of these processors is the distinction between Handler Mode…
Cortex-M0 SWDIO Access Lockout Due to Bootloader Misconfiguration The issue at hand involves a Cortex-M0-based microcontroller unit (MCU) from Sonix, specifically the SN32F247BF model, which has become inaccessible due to a misconfiguration in the bootloader code. The bootloader inadvertently disables the Serial Wire Debug Interface (SWDIO) immediately upon startup, rendering the debug interface unusable. This…
SysTick Interrupt Configuration and Debugger Disconnection Issue The core issue revolves around the STM32F767 microcontroller entering a state where the debugger disconnects upon enabling the SysTick interrupt. The SysTick timer is a fundamental peripheral in ARM Cortex-M processors, used for generating periodic interrupts for task scheduling or timekeeping. In this case, the SysTick timer is…