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$3 32-bit ARM7 SoC attacks 8-bit turf – but will it run Linux?

Oct 7, 2004 — by LinuxDevices Staff — from the LinuxDevices Archive — 9 views

[Updated Oct. 8, 2004] — Atmel is sampling the first SoC (system-on-chip) in a new line of ARM7 SoCs that it hopes can take a bite out of the 8-bit MCU (microcontroller unit) market by offering 32-bit performance at 8-bit pricing. Priced as low as $3 apiece in quantities of 10,000, the Flash-based AT91SAM7 chips incorporate small, fixed amounts of RAM and ROM that could put the squeeze on open source OS developers.

The new AT91SAM7 series chips include models with between 32KB and 512KB of ROM, and between 8KB and 64KB of RAM. They will target appliance control, utility metering, security systems, data loggers, USB-based mobile phones, and PC accessories, Atmel says — basically, any Flash-in-processor application that has traditionally been the domain of 8-bit microcontrollers.

Atmel says SoCs from the AT91 series have already been designed into industrial automation systems, MP-3/WMA players, data acquisition products, pagers, point-of-sales terminals, medical equipment, GPS units and networking systems.

The first chip in the AT91SAM7 series to reach production will be the model with 64KB of ROM, dubbed the AT91SAM7S64. Currently available to select partners, the chip will generally sample in November, and reach production in Q1, priced at $4.08 in quantities of 10,000.

The part with 32KB of ROM is expected to reach production later in Q1, priced at $2.90 in 10K quantities. The 128KB and 256KB parts will sample in Q1, while the 512KB part will sample later in 2005, according to Product Manager Tim Morin.

Additionally, Atmel is reading a version of the chip that will integrate a CAN bus and 10/100 Ethernet MAC. The AT91SAM7X128 (note the “X” in the product name) will include 128KB of ROM and 32KB of RAM.

All members of the AT91SAM7 chip family will be packaged in pin-compatible 64-pin LQFP packages, except the model with 32KB of ROM. That chip will use a 48-pin LQFP package that will nevertheless fit into the same landing as the 64-pin models. “In theory you can have a path of migration from 32KB to 512KB in the same footprint,” said Morin, who declined to specify what actual physical footprint the chips would have.

Atmel AT91SAM SoC family memory resources

Part no. Internal RAM Internal Flash
AT91SAM7S32 8 KB 32 KB
AT91SAM7S64 16 KB 64 KB
AT91SAM7S128 32 KB 128 KB
AT91SAM7S256 64 KB 256 KB
AT91SAM7S512 64 KB 512 KB
(adds CAN, 10/100)
32 KB 128 KB

In addition to an ARM7 core, the SoCs integrate a watchdog, interrupt controller, JTAG ICE (in-circuit emulator) interface, USB 2.0 device port, and various communication and control interfaces including an 8-channel 10-bit analog-to-digital converter. Click here for a complete feature chart.

Atmel's $3 SoC even includes a USB 2.0 device port
(Click above image for a more detailed diagram of the AT91SAM7S64)

Atmel also offers a development board (see photo below) that supports the entire AT91SAM7 family, according to Morin. The board is currently available as part of the AT91SAM7S64-IAR evaluation kit (photo), which also includes an AT91SAM7S64 chip, JTAG-ICE interface, project examples, and development tools “identical to those for 8-bit microcontrollers,” Atmel says, to reduce the learning curve.

The development board supports the whole chip family
(Click to enlarge)

Product Manager Jacko Wilbrink comments, “The SAM7S-series fill the gap between 8-bit microcontroller cost and 32-bit real-time performance. They provide ease and speed of application development based on familiar features with enhanced performance and security at an extremely attractive price.”

But will it run Linux?

Atmel's AT91 series of chips spans a broad range of capabilities, and includes several ARM9 based chips that run uClinux. And uClinux runs on other ARM7-based Atmel chips, such as the AT75Cxxx, in conjunction with 2MB of Flash. However, the Flash-based AT91SAMS series chips have fixed, nonexpandable amounts of RAM and Flash built into them, and those amounts are not especially large for likes of Linux.

The most capacious AT91SAMS chip offers a Flash density of 512KB, and has 64KB of RAM. These memory sizes are quite a ways off the minimum of 1MB ROM and 200KB of RAM stipulated by experts from Rt-Control, the founders of uClinux, in an article published by back in 2000. Using execute-in-place (XIP) could reduce RAM requirements, and eliminating unwanted functions would further reduce memory resource requirements, however.

Embedded developer Rob Wehrli, who wrote an article for us in 2002 comparing the size requirements of uClinux and eCos, offers stingier figures. Wehrli suggests minimum requirements of 600KB for uClinux and 60KB for eCos.

Daniel Morris of eCosCentric agrees with Wehrli's assessment. Asked if the AT91SAM7S series would support eCos, Morris replied, “The quick answer is yes. You will be governed by what your application is trying to do, but we've been doing work on the LPC2106 (and friends), tackling very similar issues, as well as having worked on the MCF5282 part. The second Atmel part (AT91SAM7S64) looks to be a reasonable choice [for eCos].”

We asked BusyBox and uClibc guru Erik Andersen for his thoughts on whether uClinux could run on these chips (before we learned of the AT91SAM7S512 with 512KB flash), and he replied, “With 64KB internal RAM, that is definitely large enough to do something useful. As for the internal flash — it might be feasible to run a very very stripped down linux kernel with 256KB flash, but very little else. I've run uClinux systems with only 1MB of RAM and 1MB flash. Much less, and it is terribly hard to do anything useful. The Game Boy Advance is [based on] an ARM7TDMI with only 256KB of flash, and people have run uClinux on it, but they cheat and run the kernel XIP from the Game Pak (AKA cartridge) ROM.”

So, what do you think? Will uClinux run on these chips? . . . eCos?


Do you think uClinux will port successfully to these super-low-cost ARM7 Atmel chips? . . . eCos? Post your thoughts and comments here.

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