Architectures and Processors

ARM Cortex-M4 DISDEFWBUF Setting Impact on MPU Functionality The ARM Cortex-M4 processor is a widely used embedded processor known for its balance of performance and power efficiency. One of its key features is the Memory Protection Unit (MPU), which provides memory region protection and access control. However, when combined with specific settings in the Auxiliary…

ARM Cortex-M7 External RAM Cache Policy Discrepancy The ARM Cortex-M7 processor, as used in the STM32F746 microcontroller, provides a Memory Protection Unit (MPU) that allows developers to configure memory regions with specific attributes, including cache policies. The default cache policy for the External RAM memory region (0x60000000 – 0x7FFFFFFF) is Write-Back Write-Allocate (WBWA), as documented…

Floating-Point Performance Degradation in ARM Cortex-M4 with FPU The ARM Cortex-M4 microcontroller, equipped with a Floating-Point Unit (FPU), is widely used in embedded systems for applications requiring efficient mathematical computations. However, developers often encounter unexpected performance degradation when performing floating-point operations, particularly when dealing with mixed data types or improper initialization of floating-point constants. This…

ARM Cortex-A9 Cacheability Control via Page Table Entries In ARMv7 architectures, such as the ARM Cortex-A9, memory cacheability is controlled through specific bits in the Page Table Entries (PTEs). The Cortex-A9 employs a two-level translation table system, consisting of the Page Global Directory (PGD) and the Page Table Entry (PTE). The PTE contains critical bits…

ARM Cortex-M7 Boot Process and Vector Table Initialization in ITCM RAM The ARM Cortex-M7 processor, as used in the STM32F769 microcontroller, has a sophisticated boot process that involves multiple memory regions, including Flash, ITCM RAM, and DTCM RAM. The boot process is critical for ensuring that the processor starts executing code correctly, and it involves…

ARM Cortex-A57 Debug State and EDITR Write Error Overview The issue at hand involves the ARM Cortex-A57 processor entering debug state and encountering an error after a write operation to the EDITR (External Debug Instruction Transfer Register). Specifically, the EDSCR (External Debug Status and Control Register) ERR bit is set following the write operation, indicating…

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…