Embedded Design
Cortex-M3 MCU offers high speed USB
Posted:04 Jun 2009
Atmel Corp. has released its first Cortex-M3ÿMCU that aims to differentiate from the rest by offering high speed USB functionality, firmware protection, differential input ADC and 1.62V core voltage.
When asked what differentiates Atmel from the other Cortex competitors, Product Marketing Manager Jacko Wilbrink offered this assesment: "The majority of other Cortex M3-based devices are targeted to low and mid-level data rate applications. We have built an ARM9-type infrastructure around our M3 core, with lots of DMA options, multi-layer busses and segmented memories that can support high-end communication from high speed USB, SDIO, MMC and SPI."
Atmel used their experience designing high speed USB for their SAM9 product line and have been able to port the design to the lower power, lower speed Cortex-M3. The SAM3U is currently the only Cortex-M3 design to offer high speed USB. Building on their experience with high speed interfaces in general, the SAM3U also contains SDIO/SD/MMC host and SPI interfaces on-chip.
Borrowing from Atmel's experience in smart card market, the SAM3U also features an on chip memory protection unit (MPU) and a 128-bit unique ID (for every device) that both can be used to protect the firmware both on-chip, and in an external memory device. As more resources get poured into firmware developement than hardware, protecting the algorithms that make the system work becomes more important. The added security might be just enough to dissuade a potential counterfeiter.
The device also has a high data-bandwidth architecture with a 5-layer bus matrix, 23 DMA channels and distributed on-chip memory including up to 52KB of SRAM split into three blocks and up to 256KB of flash in two banks. The dual bank flash offers in-application programming (IAP) where one memory bank is written with a new version of the firmware while the processor executes from the other bank. A programmable boot feature enables switching between the two flash banks at the next MCU reboot. Additional features include 12- and 10-bit ADCs, 5 UARTs, dual I2C, I2S, timers, and power and reset management. The SAM3U's supply voltage ranges from 1.62 to 3.6V. The SAM3U is aimed at applications such as high speed gateways in industrial, medical, data processing and telecom.
Further technical details, including code compatibility, pricing and availability, follow.
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| Block diagram of Atmel AT91SAM3U (Click to view full image) |
96 MHz, high bandwidth Cortex-M3 MCU
The SAM3U flash MCU has a maximum clock rate of 96 MHz at 1.8V, 85°C and integrates high data rate peripherals including a 480Mbps high-speed USB device, 384Mbps 1/4/8-bit MMC 4.3 Host, 192Mbps 1/4-bit SDIO/SDCard 2.0, 48Mbps SPI, a 1Msample/s 12-bit ADC and a 500+Mbps external bus interface. A combination of a 5-layer system bus matrix, dual peripheral bus, 4 central DMA channels, one dedicated DMA to the high speed USB device, 17 Peripheral DMA (PDC) channels, and distributed memory of up to 52KB of SRAM split in three blocks and 256KB of flash in two banks ensures uninterrupted internal and external data flows with minimum processor overhead. The central DMA features a built-in FIFO for increased tolerance to bus latency, programmable length burst transfers that optimise the average number of clock cycles per transfer, scatter, gather and linked list operations. It can be programmed for memory-to-memory transfers or memory-to-peripheral like a high speed SPI or SDIO/SD/MMC media card interfaces (MCI). The high speed DMAs have a dedicated layer in the bus matrix for parallel data transfers. The peripheral DMA isÿintegrated in the peripheral programmer's interface and has a reduced linked list support, limited to two memory areas. The SAM3U is able to simultaneously stream several 100Mbps peripherals, process the payload and control the system.
High speed USB
The SAM3U has a high-speed (HS) USB interface which supports up to seven end-points and integrates a 4KB Dual-Port RAM configurable to store full packet payloads with up to three buffers allocated to a single end-point to store micro-frames. End-Point types are configurable as bulk, interrupt, isochronous and control. With the exception of the control end-point all others are connected to a dedicated DMA and a bus layer on the matrix to sustain the high data bandwidth. The bulk mode offers the highest bandwidth with 53.24 MB/s or 425Mbps.
The payload streaming on the HS USB interface can be loaded from or stored in, for example, an SD Memory Card or on- or off-chip memory. After an optional data processing with the Cortex-M3 processor clocked at up to 96 MHz, the data can be repacked for a different protocol and transmitted over alternative high speed interfaces assisted by a total of 23 DMA-channels, like the SDIO interface supporting up to 192Mpbs in 4-bit mode, the MMC up to 384Mbps in 8-bit mode, an ASSP or FPGA connected to the external bus interface supporting more than 500Mbps or the SPI interface with up to 48Mbps.
Code confidentiality on the SAM3U with an external bus interface
The SAM3U offers code protection when storing all the firmware running in privileged mode in the on-chip flash memory. The on-chip memory protection unit (MPU) prevents execution of firmware running in privileged mode from external memory, and a hardware security bit disconnects the debug and test ports from the outside world. Furthermore a 128-bit unique ID on the SAM3U supports authentication of externally stored programs, thereby enabling the protection of externally stored firmware. The on-chip MPU also protects the SAM3U from device malfunction by restricting individual applications from accessing the memory spaces of any other simultaneously running applications.
1 Msample/s 12-bit ADC with single ended and differential input mode
The SAM3U integrates an eight channel one mega samples per second (Msample/s) 12-bit ADC with support for both single ended and differential inputs. The SAM3U is the first Cortex-M3 MCU integrating a 12-bit ADC with differential input mode support. A differential input improves noise immunity and adds support for sensors and analogue circuitry which provide differential signals only, saving an external op-amp. A programmable gain amplifier increases the range of small signals that can benefit from the full scale 12-bit resolution. Small signals can be amplified up to 4 times. A second 10-bit ADC with up to eight single ended inputs offers a ten times lower power consumption which makes it better suited for system surveillance in low power operating modes.
NAND flash for GB mass storage
The SAM3U integrates a high capacity SD/MMC Card interface enabling up to 32GB of storage in a removable NAND Flash card. The external bus interface (EBI) connects directly to raw SLC NAND flash via an on-chip controller integrating a 4kByte SRAM page buffer and single-bit error code correction. Other types of NAND flash with integrated controller like eMMC or LBA NAND, are supported on either the SD/MMC interface or EBI.
On-die termination preserves signal integrity
The SAM3U has integrated series resistances on the outputs with a typical value of 36 Ohms. These resistances replace the usual practice of external series resistance, and therefore reduce the BOM and PCB area used.
Code portability between SAM7 and SAM3 MCUs
The Cortex-M3 core has a completely new instruction set architecture, different from previous ARM cores. Migrating legacy ARM7 code to the CM3 requires a complete re-write of the assembler code. Atmel has taken steps to ensure maximum code portability between its ARM7-, ARM9- and Cortex-M3-based microcontrollers. Atmel's SAM7, SAM9 and Cortex-M3-based SAM3 have identical hardware abstraction layers and a unified programming model, as well as common peripherals that provide near-recompile-and-go code portability between devices.
Support eco-system
Atmel's SAM3U flash MCU is supported by a growing number of development tools, real-time operating systems (RTOS), middleware products and technical support services from third parties that include IAR, Keil, Micrium, and Segger. Atmel provides a software package with register descriptions and device drivers for all peripherals, along with project example. An evaluation board is also available
The AT91SAM3U is available in Flash memory densities of 64k, 128 and 256 kbytes and ships in 100 and 144 pin 0.5mm pitch QFP and 0.8 mm pitch BGA packages. Production volumes will be available in 4Q09, with prices starting at Rs.171.45 (US$3.50) in quantities of 10k units.
-Steve Bitton
Industrial Control DesignLine
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This article was printed from EE Times-Asia located at::
http://www.eetindia.co.in/ART_8800574469_1800001_NP_ba6a982f.HTM
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