Author: System on Chips

ARM Cortex-M4 VTOR Reset Behavior and Persistent Relocation Requirements The ARM Cortex-M4 processor, like other Cortex-M series processors, utilizes a Vector Table Offset Register (VTOR) to define the base address of the interrupt vector table. This vector table contains the initial stack pointer value and the addresses of exception handlers, including the reset handler. By…

ARM Cortex-A53 MMU Translation Table Misconfiguration in Flat-Mapped Memory The ARM Cortex-A53 processor, a widely used 64-bit core in embedded systems, relies heavily on the Memory Management Unit (MMU) for virtual-to-physical address translation and memory protection. A critical aspect of MMU configuration is the setup of the translation table, which defines memory attributes and access…

ARM Cortex-A53 Execution State Control via AA64nAA32 Signal The ARM Cortex-A53 processor, part of the ARMv8-A architecture, supports two execution states: AArch64 and AArch32. The initial execution state after reset is determined by the AA64nAA32 signal, which is a hardware input to the processor. This signal is sampled at reset and dictates whether the processor…

ARM Cortex-A9 PMU Hardware and Sampling Capabilities The Performance Monitoring Unit (PMU) in ARM Cortex-A9 processors is a critical component for profiling and performance analysis. It provides hardware counters to measure events such as cycles, instructions executed, cache misses, and branch predictions. However, the PMU’s functionality is not always straightforward, especially when integrated into System-on-Chip…

ARM Cortex-M Tail-Chaining Mechanism in Nested Vectored Interrupt Controller (NVIC) Tail-chaining is a critical optimization feature in the ARM Cortex-M series processors, specifically implemented within the Nested Vectored Interrupt Controller (NVIC). This mechanism allows the processor to handle back-to-back interrupts efficiently by minimizing the overhead associated with context switching. When multiple interrupts are pending, the…

Cortex-M7 Data Cache Activation Leading to Hardfault When MPU is Disabled The Cortex-M7 processor, known for its high performance and advanced features such as the Memory Protection Unit (MPU) and data cache (D-Cache), can sometimes exhibit unexpected behavior when these features are misconfigured or improperly managed. One such scenario involves the activation of the D-Cache…

ARM Cortex-A9 DDR, PLL, and UART Initialization Sequence The initialization of DDR (Double Data Rate) memory, PLL (Phase-Locked Loop), and UART (Universal Asynchronous Receiver-Transmitter) on an ARM Cortex-A9 processor is a critical step in bringing up a system, especially when loading a primary bootloader via JTAG. The Cortex-A9, being a high-performance processor, relies on precise…

ARM Cortex-A53 MMU Configuration Challenges in Identity Mapping The ARM Cortex-A53 processor, a popular choice for embedded systems, leverages a Memory Management Unit (MMU) to handle virtual-to-physical address translation. However, in certain bare-metal or tightly controlled environments, developers may seek to enable identity mapping—where virtual addresses (VA) directly correspond to physical addresses (PA)—without incurring the…

ARM Cortex-M7 Bit-Banding Absence and Its Impact on High-Performance Applications The ARM Cortex-M7 processor, designed for high-performance embedded applications, notably omits support for bit-banding, a feature present in earlier Cortex-M series processors such as the Cortex-M3 and Cortex-M4. Bit-banding allows individual bits within a memory region or peripheral register to be directly accessed and modified…

ARMv8-A CurrentEL Register and PSTATE Bit Mapping Confusion The ARMv8-A architecture introduces a sophisticated privilege model with four Exception Levels (ELs): EL0, EL1, EL2, and EL3. Each level corresponds to a different privilege and security context, with EL0 being the least privileged (user mode) and EL3 being the most privileged (secure monitor mode). The CurrentEL…