ARM7 MCU combines ethernet, CAN, USB, encryption with support for real-time apps

Marty Gold

eeProductCenter (08/24/2005 1:35 PM ET)

San Jose, Calif. — Broadening its ARM7-based offerings, Atmel Corp. is launching two flash microcontrollers with embedded 10/100 Ethernet MAC, CAN, full-speed (12 Mbps) USB 2.0 and a high speed AES/3DES encryption engine.

Designed for extensively networked, real-time embedded systems, the AT91SAM7X128 and AT91SAM7X256 also have a 10-bit ADC, two SPIs, SSC, TWI, three UARTs, an 8-level priority interrupt controller, and a full complement of supervisory functions. The two new 50 MIPS MCUs have 32- or 64 Kb of SRAM and 128- or 256 Kb of 25 ns flash memory that supports deterministic processing as required for real-time control systems.

“Increasingly, embedded systems are networked together using Ethernet, CAN, 802.15.4 and other protocols,” said Jacko Wilbrink, Atmel’s ARM marketing manager. “These “embedded networks” are in turn networked to the outside world via Ethernet connections to intranets or the Internet. The SAM7X architecture provides the extensive connectivity, memory and processing resources to support communication protocols securely, while offering real-time features required in real-time systems, but not previously available on 32-bit MCUs.”

Peripheral DMA controller ensures 4+ Mbps

A peripheral DMA controller (PDC) connects each SAM7X peripheral directly to on-chip memory, allowing high throughput data transfers without any processor overhead. Conventional ARM processors, which require the CPU to transfer the data one byte at a time, exhaust 55 percent of their processing resources at just 2 megabits per second (Mbps) and 100% of it at 4 Mbps. Higher data rates are not possible. In contrast, the SAM7X expends just 2% of its cycles at 4 Mbps and only 4% of its cycles at 10 Mbps.

By allowing data streams to be encrypted/decrypted in hardware and assisted by DMA, the SAM7X offers 80 Mbps AES encryption throughput, which is 20x faster than a software implementation. Considering that the data rate for full speed USB 2.0 is 12 Mbps, the CAN data rate is 1 Mbps, Ethernet at 100 Mbps and SAM7 SPI and USART peripherals can run at 25Mbps, it becomes quite clear that DMA and hardware encryption are mandatory for high throughput secure data transfers.

Configurable in full- or half-duplex modes, the SAM7X EMAC has programmable interpacket gap, support for virtual-LAN tagged frames and automatic-pause frame generation and termination. A dual mode interface offers seamless Media Independent Interface (MII) for a large selection of PHYs in Fast Ethernet applications, or a Reduced Media Independent Interface (RMII) which uses less I/O. SAM7X MCUs can be interfaced directly with POS-PHY Level 2/SPI-3-compliant devices, including standard network processors. Lossless flow-control via on-chip system buffers, eliminates the need for external memory or flow-control mechanisms. Jumbo frames of up to 10240 bytes are supported.

SAM7X processors have an embedded AES and Triple DES encryption engine which, in conjunction with the peripheral DMA controller, can encrypt or decrypt data at a rate of 80 Mbps for AES, 32.8 Mbps for DES and 20 Mbps for triple DES.

Although ARM MCUs offer excellent performance characteristics for embedded designs, they are rarely used in control applications because the code shadowing they use to boost performance makes it impossible to accurately predict the exact clock cycle of any event. Atmel, uniquely, has given the ARM7 core deterministic processing by adding 25 ns flash NVM (128- or 256-Kb) that allows the processor to fetch instructions directly from flash, with no performance penalty, thus eliminating the need for code-shadowing, and providing predictable instruction execution.

Real-time applications are interrupt-intensive and require supervisory functions to guarantee reliable performance. The conventional ARM7 architecture has only two interrupts, only one of which can be used for non-emergency interrupts. Nor do they have the supervisory functions typically found on 8- and 16-bit machines. SAM7X processors have a comprehensive suite of real-time peripherals and supervisory functions that include an 8-level priority interrupt controller, brownout detection, power-on-reset, single-supply voltage, watchdog timer, real-time clock, and RC oscillator.

For details of the chip, see the block diagram below.

 See related image

Compilers, linkers and debuggers are available for Atmel’s SAM7X MCUs from IAR, Green Hills, and Keil. An evaluation kit, the AT91SAM7X-EK, is available from Atmel at a resale price of $250 in any quantity. CMX, Micrium and FreeRTOS offer RTOSs for the SAM7X processors. TCP/IP stacks available now include uIP/lwIP (open source), Micrium C/TCP-IP (royalty-free) and CMX MicroNet (royalty-free).

The AT91SAM7X128 is available now in a 100-lead LQFP green package for $7.20 in quantities of 10,000. The AT91SAM7X256 in a 100-lead LQFP green package for $8.65.

For more details on AT91SAM7X, please check out www.atmel.com.

Atmel Corp. (408) 451-2855