ARM Cortex-M4 AHB Bus Matrix Arbitration and DMA Timing Errors The ARM Cortex-M4 microcontroller, like many ARM-based systems, utilizes the Advanced High-performance Bus (AHB) for communication between masters (such as the CPU and DMA controller) and slaves (such as ROM, SRAM, and SDRAM). The AHB Bus Matrix is a critical component that manages access to…
ARM Cortex-A53 Stage-2 MMU Misconfiguration Leading to Memory Corruption The core issue revolves around memory corruption observed after switching from Exception Level 2 (EL2) to Exception Level 1 (EL1) on an ARM Cortex-A53 processor. The system is configured with a Stage-2 Memory Management Unit (MMU) using a 64KB granule and 512MB block mappings. The Intermediate…
Core 1 MMU Configuration by Core 0 in a Dual A53 Cluster The ARM Cortex-A53 processor is a widely used 64-bit core in embedded systems, known for its power efficiency and performance. In a dual-core A53 cluster, each core operates independently, but they share resources such as the L2 cache and the AXI master interface….
GIC Distributor Register Write Latency and Visibility Guarantees The ARM Generic Interrupt Controller (GIC) is a critical component in ARM-based systems, responsible for managing interrupts across multiple cores and peripherals. One of the key aspects of the GIC architecture is the GIC Distributor, which handles the routing and prioritization of interrupts. When developing systems that…
ARM PMCCNTR_EL0 Access Trapping in KVM Guest Virtual Machines Accessing the ARM Performance Monitors Cycle Count Register (PMCCNTR_EL0) directly from a KVM-based guest virtual machine (VM) can be a challenging task due to the trapping mechanism enforced by the hypervisor at Exception Level 2 (EL2). The PMCCNTR_EL0 register is a critical component for performance monitoring,…
ARM Cortex-A Series and the Absence of Nested Virtualization (FEAT_NV, FEAT_NV2) Nested Virtualization, a feature that allows a hypervisor to run within another hypervisor, has been a topic of significant interest in the ARM ecosystem. The ARM architecture has introduced features like FEAT_NV and FEAT_NV2 to support nested virtualization, but as of the latest CPU…
ARMv9 FEAT_DoPD: Debug Power Domain Reconfiguration and Its Implications The introduction of FEAT_DoPD (Debug Power Domain) in ARMv9 architecture marks a significant shift in how debug resources are managed within DynamIQ-based cores. Historically, DynamIQ cores utilized a separate DebugBlock, which allowed for the isolation of debugging logic into its own power domain. This separation was…
BLAS Library Integration Challenges on Cortex-A9 Baremetal Systems Integrating the Basic Linear Algebra Subprograms (BLAS) library into a baremetal system based on the ARM Cortex-A9 processor presents a unique set of challenges. The Cortex-A9, known for its dual-core configuration and advanced features like out-of-order execution and NEON SIMD capabilities, is a powerful processor for embedded…
Cortex-A55 IMPDEF System Registers and Their Undocumented Behavior The Cortex-A55, a highly efficient mid-range ARM Cortex-A series processor, implements a variety of system registers that are critical for its operation. Among these, some registers fall under the IMPDEF (Implementation Defined) category, meaning their functionality is specific to the Cortex-A55 implementation and not architecturally defined by…
Cortex-A53 Write-Streaming Mode and BUS_ACCESS_LD Anomalies The Cortex-A53 processor, a widely used ARM core in embedded systems, is known for its efficiency and performance in applications ranging from mobile devices to embedded controllers. However, when operating in write-streaming mode, particularly during memory operations such as memset, unexpected behavior in Performance Monitoring Unit (PMU) counters, specifically…