Architectures and Processors

ARMv7M Instruction Encoding Ambiguity Between B.W and DSB In the ARMv7-M architecture, the encoding of certain instructions can lead to ambiguity when interpreting machine code. Specifically, the B<c>.W (Branch with condition, wide) and DSB (Data Synchronization Barrier) instructions share overlapping encoding patterns under specific conditions. This overlap arises due to the way the instruction set…

ARM Cortex-R5 SVC Exception Handling Delay The ARM Cortex-R5 processor is designed for real-time applications, where deterministic behavior and low-latency interrupt handling are critical. However, in some cases, developers may encounter unexpected delays when executing the Supervisor Call (SVC) instruction, specifically SVC #0xFF. This delay manifests as the processor continuing to execute subsequent instructions before…

SPI Data Frame Size Mismatch in ARM Cortex-M0: 16-Bit Output Instead of 8-Bit The issue at hand involves the ARM Cortex-M0 processor, specifically the STM32F030K6T6 microcontroller, where the SPI (Serial Peripheral Interface) peripheral is outputting 16-bit data frames instead of the expected 8-bit frames. This discrepancy occurs despite the SPI configuration registers being set to…

SWD Protocol Initialization and Deprecated Sequence Observation The SWD (Serial Wire Debug) protocol is a two-pin interface used for debugging ARM Cortex-M microcontrollers, including the STM32F103. During the initialization phase of the SWD protocol, the debugger (in this case, JLink EDU) communicates with the target device to establish a connection. This process involves several distinct…

ARM Cortex-A53 NEON Performance Bottlenecks in Loop Unrolling The core issue revolves around optimizing a loop that calculates the magnitude of a complex float vector using ARM Cortex-A53’s NEON SIMD (Single Instruction, Multiple Data) capabilities. The original code processes four complex float elements per iteration, leveraging NEON intrinsics for vectorized operations such as loading, multiplication,…

ARM GPT Caching Mechanisms and Hardware Implementation Variability The ARM architecture, renowned for its flexibility and scalability, provides a robust framework for memory management, including the use of Guest Page Tables (GPT) in virtualization scenarios. A critical aspect of this framework is the caching behavior associated with GPT entries, which can significantly impact system performance…

ARM Cortex-A72 Generic Timer Counter Anomalies During Multi-Core Synchronization The ARM Cortex-A72 processor, part of the ARMv8-A architecture, is widely used in high-performance embedded systems. One of its critical components is the ARM Generic Timer, which provides a system-wide synchronized counter for timing and scheduling purposes. However, a recurring issue has been observed where the…

ARM Cortex-M4 Cache Coherency Problems During DMA Transfers In ARM Cortex processors, the ACE (AXI Coherency Extensions) protocol plays a critical role in maintaining cache coherency across multiple masters. One of the key operations in this protocol is the CleanUnique (CU) transaction, which ensures that a cache line is in a unique state before a…

ARM Cache Invalidate Queue: A Hidden Mechanism in Multi-Core Systems In multi-core ARM systems, cache coherency is a critical aspect of ensuring that all cores have a consistent view of memory. One of the lesser-discussed mechanisms that play a role in maintaining this coherency is the "invalidate queue." The invalidate queue is a hardware structure…

ARM CHI Protocol and WriteEvictFull Opcode Behavior The ARM Coherent Hub Interface (CHI) protocol is a critical component of ARM’s system architecture, designed to manage cache coherency and data transfers between different nodes in a system. One of the key operations in the CHI protocol is the WriteEvictFull opcode, which is used to write back…