Architectures and Processors

ARM T32 IT Instruction: Purpose and Common Misunderstandings The ARM T32 (Thumb-2) instruction set includes the IT (If-Then) instruction, which is a powerful yet often misunderstood feature. The IT instruction is used to conditionally execute up to four subsequent instructions based on the state of the ARM condition flags. This capability is particularly useful in…

ARM Cortex-M4 Load/Store Instruction Offset Timing Anomalies The ARM Cortex-M4 processor, a widely used microcontroller core, exhibits a peculiar behavior when executing load and store instructions with specific offset values. This behavior manifests as unexpected variations in clock cycle consumption for offsets starting from 30 (decimal) and beyond. The anomaly is particularly noticeable when the…

ARM Cortex-M Boot and Remap Signal Functionality in System Design Kit The relationship between BOOT and REMAP signals in ARM Cortex-M System Design Kits (CMSDK) is a critical aspect of system initialization and memory mapping. These signals are often misunderstood due to their nuanced behavior and the lack of explicit documentation in some design kits….

LPC1768 USB Host Capability and FAT32 Limitations The LPC1768 microcontroller, based on the ARM Cortex-M3 core, is a popular choice for embedded systems due to its robust peripheral set, including USB host capabilities. However, interfacing the LPC1768 with a 1TB external USB hard disk presents several challenges, particularly when dealing with the FAT32 file system….

GICv2 Virtualization and SPI Interrupt Handling Across vCPUs In a hypervisor environment where the Generic Interrupt Controller version 2 (GICv2) is virtualized, handling Shared Peripheral Interrupts (SPIs) across virtual CPUs (vCPUs) can introduce complex scenarios. Specifically, when an SPI targets multiple physical CPUs (e.g., CPU0 and CPU1), and the hypervisor is responsible for managing the…

ARMv8 Exception Levels and TrustZone Integration in KVM Virtual Machines The ARMv8 architecture introduces a sophisticated security model through its TrustZone technology, which partitions the system into Secure and Non-Secure worlds. This partitioning is crucial for isolating sensitive operations, such as cryptographic functions, from the rest of the system. However, when virtualization is introduced via…

ARM TrustZone and UEFI Integration Challenges in Secure Boot Flow The integration of ARM TrustZone with UEFI presents a unique set of challenges, particularly when attempting to maintain the secure boot flow while ensuring that the Secure Monitor and Secure OS operate seamlessly within the UEFI environment. The primary issue revolves around the compatibility and…

ARM Cortex-A53 Instruction Prefetching Challenges in Large Code Blocks The ARM Cortex-A53 processor, a widely used core in embedded systems and mobile devices, employs a sophisticated caching mechanism to optimize instruction and data access. However, when dealing with large blocks of code that lack function calls, ensuring efficient instruction prefetching into the L1 instruction cache…

Firmware Separation in Cortex-M3: Understanding I-RAM and D-RAM Allocation The Cortex-M3 microcontroller, based on the ARMv7-M architecture, is widely used in embedded systems due to its balance of performance, power efficiency, and cost-effectiveness. One of its key features is the separation of the I-CODE and D-CODE buses, which allows for simultaneous instruction fetches and data…

ARM Cortex-A Cache Coherency Problems During DMA Transfers In ARMv7-A based multiprocessor systems, ensuring cache coherency during Direct Memory Access (DMA) operations is critical for reliable data transfers. The issue described involves a scenario where a DMA engine (SDMA) occasionally copies stale data from memory, despite the use of cache cleaning and Data Synchronization Barriers…