Cortex-R Series

Cortex-R processors are designed for demanding real-time solutions and are commonly used in ASIC, ASSP and MCU System-on-Chip applications. The family has three members, Cortex-R4, Cortex-R5 and Cortex-R7 and these are the markets for which those products have been specifically designed:

These applications exhibit a common requirement set, illustrated by the following examples:

Mobile handsets are introducing high data rate wireless broadband to deliver feature-rich, audio, video and Internet services to users. Handset processing for the fourth generation and long-term evolution of mobile technology requires complex software protocol stacks to run in real-time, managing mobility, connection, security, data traffic and the air interface modem. Advanced multi-core SoCs use Cortex-R processors for these tasks, complementing Cortex-A series processors for user applications. Low cost and power consumption continue to be key success criteria for mobile handset products.

Hard disk drives continue to be one of the most demanding applications for embedded processors and Cortex-R has been adopted by most major manufacturers. High growth in enterprise networks and Internet data centers is driving an exponential rise in storage capacity. Elsewhere, consumers keep their stock of music and movies on PC disks and Network Attached Storage (NAS) devices. More data requires more bandwidth and the latest drives support data traffic using USB-3 at 4 Mbps and SATA at 6 Mbps. Within the drive, high speed servo control systems manage disk rotation and head position, and read/write channels process signals at very high data rates.

Automotive Electronic Control Units (ECUs) are widely adopted in modern cars and trucks. In addition to engine management and entertainment applications, there is increasing reliance on driver assistance and safety systems for applications such as vehicle stability, steering, anti-lock braking, collision avoidance and air bag deployment. These systems require high performance processing as they read data from a variety of sensors, perform computation that often uses floating point algorithms and deliver the necessary control signals. Above all, such systems must perform to their real-time constraints with high reliability.

Take a look at the Family Features page to read more about what the three Cortex-R processors provide for those markets.

Essential characteristics of Cortex-R real-time processors in these applications are:

• Fast – high processing performance at high clock frequency.
• Deterministic – processing must meet hard real-time constraints on all occasions.
• Safe – systems must be reliable and dependable. Some will be safety-critical.
• Cost-effective – competitive cost and power consumption, both in the processor and its memory system.

High Performance

High efficiency and high frequency for real-time applications

Cortex-R processors all employ a high performance, deeply pipelined micro-architecture for operation at high clock frequencies, approaching 1 GHz on 40 nm G processes. This micro-architecture includes instruction pre-fetching, queuing and branch prediction to maintain the flow of instructions for execution. Hardware dividers and floating point units are included and the processors have superscalar capabilities, whereby instructions which do not require conflicting resources may be executed in parallel. ARM’s AMBA 3 AXI (Advanced eXtensible Interface) busses are used to maximize performance when accessing memory and peripherals. Starting with Cortex-R4, these processors are capable of 1,500 Dhrystone MIPS performance on a 40 nm G process.

Real-Time

Delivering deterministic behavior for high-reliability

Real-time systems are supported by Cortex-R processors with a fast and deterministic response to events and interrupts. A choice of interrupt interfaces and external interrupt controllers allows SoC designers to optimize between response time and features such as the number of interrupts, interrupt masks and prioritization. Any instructions that could delay interrupt response by more than a few cycles can be stopped and restarted. Cortex-R processors also feature a Tightly-Coupled Memory (TCM) interface to local RAM or Flash memory that can be arranged to hold instructions or data that are always immediately available for processing. TCMs may be used to hold interrupt service routines or other code for time-critical events. Fast data can be read into or out of TCM using DMA via a dedicated AXI slave bus interface. These features enable systems to respond rapidly and deterministically to real-time events.

Flexible Cost and Power Efficiency

Configurable for feature-rich and cost-sensitive applications

A key aspect of the Cortex-R series is configurability, allowing designers to select features of the processor for a precise match with application requirements.  These options enable Cortex-R processors to address a wide range of embedded applications and designers can trade off features and performance against power consumption, area and cost of the final ASIC or ASSP device. For example:

• High availability – systems that are always ready to offer service, e.g. respond to an event.
• Reliability – systems that can be relied upon to respond correctly and on-time, every time.
• Maintainability – systems that can be monitored, repaired and upgraded, often while still operating.
• Fault tolerant – continued operation in the event of a fault occurring, or at least detecting fault conditions.
• Safety critical – suitable for use in applications where failure may cause damage.
• Secure – proof against unintended or unauthorized modification.

Many features of Cortex-R series processors address these requirements making the processors suitable for use in ASICs, ASSPs or MCUs intended for use in applications such as vehicle braking, steering or anti-skid. Applications such as mobile baseband or hard disk drive also rely on some of these characteristics to ensure connections or data are not lost, e.g. deterministic interrupt response time or detection of data errors.

Cortex-R processor features that may be employed and configured for dependable systems include:

• ARM v7 architecture. In common with earlier versions of the ARM architecture, v7 specifies software operating modes for processors that distinguish between user applications and privileged programs such as the operating system, interrupt and exception handlers. Certain instructions are only available in privileged modes and these can be used by operating systems whilst applications are prevented from making unauthorized access to areas of memory or peripheral.
• MPU. The Memory Protection Unit monitors all accesses to memory and memory-mapped peripherals and can be configured to report or prohibit access to regions by selected software tasks. Working in conjunction with the processor’s user and privileged modes, the MPU provides a comprehensive capability to monitor selected regions in the address map and trap unauthorized access caused by misbehaving code due to programming flaws, error conditions or security breaches.
• Parity. Parity checking is built in to Cortex-R processors, providing an automated capability to detect, and in some cases correct, parity errors in level-1 memory (e.g. cache and TCM) together with interfaces for external parity circuits.
• ECC. Error Correction Code handling is also built in to Cortex-R processors enabling single bit errors to be automatically corrected by the processor. Multi-bit errors are detected but cannot always be corrected. Interfaces for external ECC circuits are also present.
• Lock-step. The Cortex-R processors are designed for configuration and synthesis to create a redundant processor in a lock-step configuration whereby an error in either of the processors is detected by checking logic.

These and other features make real-time ARM processors such as Cortex-R4 suitable for use in systems that must operate to a Safety Integrity Level (SIL) as defined by IEC61508 or ISO26262. In automotive applications these systems will run an AUTOSAR-compliant RTOS.

ARM Connected Community members and other organizations offer tools and software for Cortex-R processors such as Compilers, Debuggers and Real-Time Operating Systems. There are also providers of specific hardware and software products such as microcontroller hardware and mobile baseband protocol stack software. Click on these logos to find out more: