ARM Cortex Performance Monitors: Speculative Execution Event Ambiguity The ARM Architecture Reference Manual (ARM ARM) introduces the concept of "Speculatively executed" instructions in the context of Performance Monitors Extension. The manual defines a speculatively executed instruction as one that might be speculative, and this definition is tied to events such as INST_SPEC. However, the term…
Secure and Non-Secure Memory Overlap in ARM A-Profile Systems In ARM A-Profile architectures, particularly those implementing the ARMv8-A and ARMv9-A instruction sets, the concept of secure and non-secure memory spaces is fundamental to the TrustZone security model. TrustZone partitions the system into two worlds: the Secure world and the Non-Secure world. Each world has its…
ARM Activity Monitor (AMU) vs. Performance Monitor Unit (PMU): Key Differences and Use Cases The ARM Activity Monitor (AMU) and Performance Monitor Unit (PMU) are both critical components in ARM architectures, particularly in ARMv8.4-A and later. While they share similarities in their ability to count events, their roles, design, and use cases differ significantly. The…
ARM Cortex-A MMU Configuration and Execution Permission Faults The ARM Cortex-A series of processors, widely used in embedded systems and high-performance applications, relies heavily on the Memory Management Unit (MMU) for virtual memory management, memory protection, and access control. One of the most common issues encountered when configuring the MMU is the execution permission fault,…
Understanding the MIDR Register and PartNum Field The Main ID Register (MIDR) is a critical component in ARM architectures, providing essential information about the processor’s identity. The MIDR register is part of the ARMv8-A architecture and is accessible via the MIDR_EL1 system register. It contains several fields, including the Implementer, Variant, Architecture, PartNum, and Revision….
ARM Cortex-R52 Exception Triggering via UDF Instruction in A32 and T32 The ARM Cortex-R52 processor, designed for real-time and safety-critical applications, supports both the A32 (ARM) and T32 (Thumb) instruction sets. A common requirement in embedded systems is to ensure that any unintended execution of code from unused memory regions triggers an exception. This is…
Understanding AHB5 Burst Transfers: SINGLE vs. INCR with NONSEQ and SEQ The AHB5 protocol, a key component of the Advanced Microcontroller Bus Architecture (AMBA), is widely used in ARM-based systems for high-performance data transfers between masters and slaves. One of the critical aspects of AHB5 is its support for burst transfers, which allow multiple data…
GICv3 Hypervisor Control Register (ICH_HCR_EL2) and List Register Entry Non-Present Interrupt Enable (LRENPIE) The Generic Interrupt Controller version 3 (GICv3) is a critical component in ARM-based systems, managing interrupt handling for both physical and virtualized environments. One of the key features of GICv3 is its support for virtualization, which allows hypervisors to manage interrupts for…
ARM Cortex-A55 Cache Coherency and Snoop Response Protocol The ARM Cortex-A55 processor, part of the ARMv8-A architecture, implements a sophisticated cache coherency mechanism to ensure data consistency across multiple cores and system components. One critical aspect of this mechanism is the snoop response behavior, particularly when dealing with clean cache lines. In a system where…
ARM NEON Memory Copy Performance Discrepancy When implementing memory copy operations using ARM NEON intrinsics, developers often expect significant performance improvements over standard library functions like memcpy. However, in many cases, the observed performance gain is marginal, as seen in the example where a NEON-optimized buffer copy only achieved a 3.5% improvement over memcpy. This…