Author: System on Chips

ARM AArch64 Instruction Encodings: UNDEFINED vs. Unallocated Behavior The ARM AArch64 architecture defines specific behaviors for instruction encodings that are either UNDEFINED or unallocated. These terms are critical for understanding how the processor handles invalid or reserved instruction patterns, and they have significant implications for software compatibility and forward compatibility across different versions of the…

ARM Cortex-A72 GICv3 Interrupt Handling Issues During EL3 to EL1 Transition The ARM Cortex-A72 processor, when paired with the Generic Interrupt Controller (GIC) version 3, can exhibit complex interrupt handling issues during transitions between Exception Levels (ELs), particularly when moving from EL3 to EL1. These issues often manifest as interrupts not being correctly handled after…

Cortex-A9 Atomic Variable Deadlock in Multi-Core Bare-Metal Systems In multi-core ARM Cortex-A9 systems, particularly in bare-metal environments, implementing atomic operations across cores can lead to deadlocks or infinite loops if the memory management unit (MMU) configuration is not properly set up. This issue often manifests when using atomic variables in shared memory regions, where one…

Cortex-R52 GICv3 Interrupt Handling Sequence and Stack Overflow The Cortex-R52 processor, when paired with a GICv3 interrupt controller, can experience a critical issue during interrupt handling where the processor fails to restore the context after handling an interrupt. This issue manifests when interrupts are triggered frequently, and the IRQ is unmasked before writing to the…

ARM Cortex-A76 and DSU Cache Way Partitioning Misbehavior Cache way partitioning is a critical feature in modern ARM processors, particularly in multi-core systems where shared resources like the Last Level Cache (LLC) must be managed efficiently to ensure predictable performance. The ARM Cortex-A76, coupled with the DynamIQ Shared Unit (DSU), supports cache way partitioning to…

Understanding the UD State and MakeInvalid Transaction Requirements The ARM AMBA Coherent Hub Interface (CHI) specification defines a set of cache states and transactions that ensure coherency across multiple request nodes (RNs) in a system. One such state is the UD (Unique Dirty) state, which indicates that the cache line is held exclusively by the…

L2 Cache ECC Single-Bit Correctable Error Notification Mechanism The ARM Cortex-A72 processor incorporates Error Correction Code (ECC) mechanisms within its L2 cache to detect and correct memory errors. ECC is critical for ensuring data integrity, particularly in safety-critical and high-reliability systems. The Cortex-A72 L2 cache ECC system can handle both single-bit correctable errors and double-bit…

Memory Reconstruction Port: Purpose and Role in Cortex-R Processors The Memory Reconstruction Port (MRP) in ARM Cortex-R series processors is a specialized feature designed to facilitate advanced debugging and system recovery scenarios, particularly in safety-critical and real-time embedded systems. The MRP allows external access to the processor’s internal memory and system state, even when the…

ARM Cortex-M4 Stack Pointer Misalignment During Task Initialization The ARM Cortex-M4 processor, like other ARMv7-M architecture-based processors, enforces strict alignment requirements for stack pointers. The stack pointer (SP) must always be aligned to an 8-byte boundary, as mandated by the ARM Architecture Reference Manual. Misalignment of the stack pointer can lead to unpredictable behavior, including…

Cortex-M7 UsageFault Handler Misrouting Due to Incorrect Link Register Management The core issue revolves around the improper handling of the Link Register (LR) during exception handling in an ARM Cortex-M7 microcontroller. Specifically, the problem manifests when attempting to return from a UsageFault exception triggered by an unaligned memory access. The handler, UsageFault_Handler, is designed to…