Engineering:CMD640

CMD 640b PCI IDE controller

CMD640, the California Micro Devices Technology Inc product 0640, is an IDE interface chip for the PCI and VLB buses. CMD640 had some sort of hardware acceleration: WDMA and Read-Ahead (prefetch) support.

CMD Technology Inc was acquired by Silicon Image Inc. in 2001.

Chip	Protocol
SiI/CMD 640	MDMA 1
SiI/CMD 643	MDMA 2
SiI/CMD 646	UDMA 2
SiI/CMD 648	UDMA 4
SiI/CMD 649	UDMA 5
SiI0680	UDMA 6

Hardware bug

The original CMD640 has data corruption bugs, some of which remained in CMD646. The data corruption bug is similar to the bug affecting the contemporaneous PC Tech (a subsidiary of Zeos) RZ1000 chipset. Both chipsets were used on a number of motherboards, including those from Intel.

Мodern operating systems have a workaround for this bug by prohibiting aggressive acceleration mode and losing about 10% of the performance.

External links

• File containing technical information, FAQs, and tests regarding the corruption issues
• Linux's description of how it deals with the CMD640 corruption
• IBM: July 10, 1998 - Warp FixPak TIPS (includes section on how to detect and mitigate CMD640 concerns)
• EIDE flaw