Architectures and Processors

AXI Outstanding Transactions and Memory Latency Impact on Read/Write Symmetry The core issue revolves around the performance implications of AXI (Advanced eXtensible Interface) outstanding transactions when interfacing with a memory subsystem that exhibits variable latency characteristics. Specifically, the concern is whether read and write transactions will exhibit symmetrical latency behavior when the memory subsystem has…

Cortex-M3 Program Optimization Challenges with Large Test Data Sets When optimizing program variations for a Cortex-M3 microcontroller, one of the primary challenges is the need to process large amounts of input test data to assess performance differences between variations. Running these tests on actual hardware, such as a PCB with a Cortex-M3, can be prohibitively…

APB4 Protocol Signal Assertion Timing Ambiguity for PSTRB and PPROT The Advanced Peripheral Bus (APB) protocol, part of the ARM AMBA family, is widely used for low-bandwidth, low-power peripheral interfacing in SoC designs. The APB4 specification (IHI0024C) introduces two critical signals: PSTRB (Write Strobe) and PPROT (Protection Signal). These signals enhance the functionality of the…

ARM Cortex-M4 Decimal to Hexadecimal Conversion Challenges The process of converting decimal unsigned integers to hexadecimal unsigned integers without relying on standard library functions such as printf or strol presents a unique set of challenges, particularly in embedded systems where resource constraints and performance optimization are critical. This issue is especially relevant in ARM Cortex-M4…

AXI4 Point-to-Point Interface and Its Architectural Implications The AXI4 protocol, as defined by ARM, is fundamentally a point-to-point interface, meaning it is designed to connect a single master to a single slave. This architectural choice has significant implications for the design and implementation of systems-on-chip (SoCs) that utilize the AXI4 protocol. Unlike older protocols such…

Tidemark Functionality in AXI Interconnect and Its Impact on AWREADY The Tidemark functionality in the AXI Interconnect PL301 r2p3 is a critical feature that governs the flow control of write transactions between AXI masters and slaves. Tidemark is essentially a threshold mechanism that determines when the interconnect should stall or allow the release of write…

Cortex-M3 Multicore Debugging with Single JTAG/SW Interface When designing a multicore system with multiple instances of ARM Cortex-M3 processors, one of the critical challenges is providing an efficient and scalable debugging interface. Each Cortex-M3 core typically comes with its own Debug Access Port (DAP), which supports both JTAG and Serial Wire (SW) debugging protocols. However,…

Evolution of AMBA AHB Protocol Generations The AMBA AHB (Advanced High-performance Bus) protocol has undergone significant evolution since its inception, with three major releases that have adapted to the changing requirements of system-on-chip (SoC) designs. Each generation of the AHB protocol has introduced new features, optimizations, and simplifications to address the growing complexity and performance…

AMBA APB Wait States: Impact on Read/Write Transactions and Peripheral Timing The Advanced Peripheral Bus (APB) is a key component of the ARM Advanced Microcontroller Bus Architecture (AMBA) protocol suite, designed for low-power, low-complexity peripheral communication. One of the critical features introduced in AMBA 3 APB is the PREADY signal, which enables the insertion of…

AMBA APB Frequency Limitations and System Complexity The Advanced Microcontroller Bus Architecture (AMBA) Advanced Peripheral Bus (APB) is a low-cost, low-power interface designed for connecting peripherals to a system-on-chip (SoC). Unlike high-performance buses such as AXI or AHB, APB is optimized for simplicity and ease of integration. However, one of the most common questions surrounding…