Author: System on Chips

AXI4 Write Data Transmission Preceding Address Information The AXI4 protocol, a cornerstone of modern ARM-based systems, allows for a unique scenario where write data (W) can be transmitted before the corresponding write address (AW). This feature, while seemingly counterintuitive, is deeply rooted in the protocol’s design to optimize performance and flexibility in complex systems. At…

ARMv8 Cache Management: Clean vs. Invalidate Operations in U-Boot The U-Boot bootloader, particularly in the ARMv8 architecture, implements cache management through assembly files such as cache.s. One of the key points of confusion arises from the conditional logic that determines whether to perform a clean and invalidate operation or just an invalidate operation based on…

ARMv8-A EL2 System Register Access Trapping to EL3: Architectural Limitations and Use Cases In the ARMv8-A architecture, the Exception Levels (ELs) define the privilege and security levels at which software operates. EL3 is the highest privilege level, often referred to as the "secure monitor" level, responsible for managing transitions between the secure and non-secure states….

L2C-310 Cache Line Partial Flush During Clean & Invalidate Operations The ARM Cortex-A9 processor, when paired with the L2C-310 cache controller, can exhibit a non-deterministic issue where the L2 cache clean and invalidate (clean&inval) operation only partially flushes a cache line to the L3 memory. This issue is particularly observed under heavy memory load conditions,…

Cortex-A53 EL2 to EL1 Transition Failure and System Hang The Cortex-A53 processor, part of ARM’s Cortex-A series, is a widely used 64-bit ARMv8-A core that supports multiple exception levels (ELs). These exception levels provide a hierarchical privilege model, with EL3 being the most privileged (secure monitor), followed by EL2 (hypervisor), EL1 (operating system), and EL0…

Cortex-M3 DesignStart Bitstream Incompatibility with Arty A7-100T FPGA The Cortex-M3 DesignStart FPGA-Xilinx edition package provides a pre-built bitstream for the Arty A7-35T FPGA board. However, users attempting to load this bitstream onto the Arty A7-100T FPGA board encounter an error: "Incorrect bitstream assigned to device. Bitfile is incompatible for this device." This issue arises because…

Cortex-A55 Performance Monitoring Unit (PMU) Counter Access Issues The Cortex-A55, a high-efficiency CPU in ARM’s DynamIQ family, incorporates a Performance Monitoring Unit (PMU) that provides critical insights into system performance through hardware counters. These counters track events such as cache misses, branch mispredictions, and instruction execution cycles, enabling developers to identify bottlenecks and optimize software….

Exclusive Access Failures in Multitasking Scenarios with LDREX/STREX The ARM architecture provides a mechanism for atomic operations through the use of Load-Exclusive (LDREX) and Store-Exclusive (STREX) instructions. These instructions are designed to facilitate synchronization in multiprocessing or multitasking environments by allowing a processor to attempt an atomic read-modify-write operation. However, the proper functioning of LDREX…

NSCFG Bit Functionality in S2CRn Register and Its Impact on Translation Table Walks The NSCFG (Non-Secure Configuration) bit in the S2CRn (Stream-to-Context Register n) register of the SMMUv2 (System Memory Management Unit version 2) architecture plays a critical role in determining the security state of translation table walks. When the NSCFG bit is set for…

NRF9160 CMSIS DSP Library Integration and Code Size Explosion When integrating the CMSIS DSP library into an NRF9160 project using the ARM Cortex-M33 core, developers often encounter significant code bloat. This issue arises when enabling multiple CMSIS DSP modules (e.g., FastMath, ComplexMath, Statistics, and Transform) via configuration flags in the Zephyr build system. The resulting…