Architectures and Processors

ARMv7 Exception Handling: Preferred Return Address and Link Register (LR) Calculation When dealing with exception handling in ARMv7-A and ARMv7-R architectures, one of the most critical aspects is determining the correct return address after an exception has been serviced. The return address is the location in memory where the processor should resume execution once the…

ARM Cortex-A53 Data Abort Exception 0x96000035 During Stage-2 Translation The issue at hand involves an ARM Cortex-A53 processor running Linux on a TI platform with two clusters, each containing two cores. The system is configured to run in HYP mode (Hypervisor mode, EL2) with stage-2 translation enabled. When stage-2 translation is active, a data abort…

ARMv8-A AArch32 Short Descriptors vs. Long Descriptors: A Comparative Analysis The ARMv8-A architecture, which supports both AArch32 and AArch64 execution states, provides two distinct translation table formats for memory management in the AArch32 state: short descriptors (32-bit) and long descriptors (64-bit). While the long descriptor format is more versatile and capable of handling a broader…

ARM Cortex-AArch64 Backward Compatibility Expectations vs. ThunderX Reality The ARM architecture has long been celebrated for its backward compatibility, particularly with the introduction of ARMv8-A, which brought the AArch64 execution state alongside the existing AArch32 state. This dual-state architecture was designed to allow seamless execution of 32-bit applications on 64-bit processors, ensuring a smooth transition…

ARM Cortex-M3 Peripheral Register Access Failures During Interrupt Handling When working with ARM Cortex-M3 microcontrollers, developers often encounter issues related to peripheral register access, particularly when using Read-Modify-Write (RMW) operations in interrupt-driven contexts. The problem arises when attempting to modify specific bits in peripheral registers using standard C operations such as |= (bitwise OR) and…

ARM Cortex-A55 MMU Page Table Entry Updates and Cache Coherency Requirements The ARM Cortex-A55 processor, like many modern ARM cores, relies on a Memory Management Unit (MMU) to handle virtual-to-physical address translation. The MMU uses page tables stored in memory to perform these translations. When a page table entry (PTE) is modified, the MMU must…

Cortex-M0 DesignStart Debug Interface Configuration and SWD Connection Failures The Cortex-M0 DesignStart Eval platform is a popular choice for prototyping ARM Cortex-M0-based systems on FPGAs. However, one of the most common challenges engineers face is establishing a successful Serial Wire Debug (SWD) connection between the debug probe (e.g., STLink2) and the Cortex-M0 DesignStart implementation. This…

ARM Cortex-A64 and x86: The Shift Away from Conditional Execution Conditional execution, a feature prominently available in earlier ARM architectures such as ARMv7 and ARMv6, allowed instructions to be executed based on the state of specific condition flags. This feature was particularly useful for reducing the number of branch instructions, thereby improving code density and…

ARM Cortex-M ADC Data Corruption with Unexpected Prefix "a20.00000" When working with ARM Cortex-M microcontrollers, reading data from an Analog-to-Digital Converter (ADC) is a common task. However, unexpected results such as the prefix "a20.00000" appearing in the ADC read data can be perplexing. This issue often manifests when the ADC data is transmitted to a…

ARM Cortex-A35 Low-Power Mode Transition Latency and Cache Coherency The ARM Cortex-A35 is a highly efficient processor designed for low-power applications, often used in embedded systems where energy efficiency is critical. One of the key features of the Cortex-A35 is its ability to transition into low-power modes to conserve energy. However, these transitions are not…