AXI Fixed Burst Mechanism and WSTRB Signal Interpretation The AXI (Advanced eXtensible Interface) protocol is a widely used on-chip communication standard for high-performance embedded systems. One of its key features is the ability to perform burst transfers, which allow multiple data transactions to occur in a single operation. Among the burst types supported by AXI,…
Enabling L2 Cache for MMU Page Tables in Cortex-A9 The ARM Cortex-A9 processor, commonly used in embedded systems, provides a Memory Management Unit (MMU) that supports virtual memory management through page tables. These page tables are typically stored in DDR memory, which is often configured as non-cacheable by default to ensure coherency and avoid stale…
AXI ID Bit Width Mismatch in Multi-Processor Systems with A15 and R7 Cores In multi-processor ARM systems, integrating different cores such as the Cortex-A15 and Cortex-R7 on separate AXI buses can introduce challenges when attempting to establish communication between the two systems. One such challenge is the conflict arising from the AXI ID bit width…
ARM Cortex-M4 Processor Architecture and Command Execution Flow The ARM Cortex-M4 processor is a highly efficient 32-bit RISC processor designed for embedded applications, particularly those requiring digital signal processing (DSP) capabilities. To understand what happens inside the Cortex-M4 when it executes a command, such as changing the color of a smart bulb, we need to…
Cortex-A35 DDR3 Read Access Latency and Bandwidth Discrepancies The Cortex-A35, a power-efficient ARMv8-A processor, is designed for low-power applications but still requires careful tuning to achieve optimal memory performance. In this analysis, we focus on the observed discrepancies between DDR3 read and write bandwidths, specifically in the context of the i.MX 8X SoC with DDR3L-1866…
ARMv8-M MPU Access Control Limitations and NULL Pointer Protection The ARMv8-M architecture introduces a Memory Protection Unit (MPU) that is designed to provide memory access control for embedded systems. Unlike its predecessor, the ARMv7-M MPU, the ARMv8-M MPU simplifies the access permission (AP) field to two bits, which limits the granularity of access control configurations….
ARMv7-M Speculative Data Fetching Mechanism and Behavior Speculative data fetching is a critical performance optimization technique employed in ARMv7-M architectures, particularly in implementations like the Cortex-M7. This mechanism allows the processor to preemptively fetch data from memory before it is explicitly required by the executing instructions. The goal is to reduce memory access latency, which…
Misaligned Physical Address in 2MB Block Mapping Configuration The core issue revolves around the misconfiguration of the ARM Memory Management Unit (MMU) in AArch64 mode, specifically when attempting to map 2MB blocks. The user successfully mapped 4KB blocks but encountered unexpected behavior when transitioning to 2MB block mappings. The primary symptom is that virtual addresses…
ARM Cortex A76 ASIMD Instruction Latency and Pipeline Utilization The ARM Cortex A76 is a high-performance processor core designed for mobile and embedded applications, featuring Advanced SIMD (ASIMD) instructions that accelerate data-parallel operations. A critical aspect of optimizing code for the Cortex A76 is understanding the latency and throughput of ASIMD instructions, particularly those utilizing…
ARM Cortex-M Structure Padding Stability in Persistent Data Storage When developing embedded systems for ARM Cortex-M processors, a common practice is to store persistent data in non-volatile memory such as serial NOR-flash. A developer might choose to directly stream C/C++ structs to flash memory without serialization, relying on the ARM Architecture Procedure Call Standard (AAPCS)…