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NetBSD 6.1.5 - man page for geodeide (netbsd section 4)

GEODEIDE(4)			   BSD Kernel Interfaces Manual 		      GEODEIDE(4)

     geodeide -- AMD Geode IDE disk controllers driver

     geodeide* at pci? dev ? function ? flags 0x0000

     The geodeide driver supports the AMD Geode CS5530A and SC1100 IDE controllers, and provides
     the interface with the hardware for the ata(4) driver.

     The 0x0002 flag forces the geodeide driver to disable DMA on chipsets for which DMA would
     normally be enabled.  This can be used as a debugging aid, or to work around problems where
     the IDE controller is wired up to the system incorrectly.

     ata(4), atapi(4), intro(4), pci(4), pciide(4), wd(4), wdc(4)

     The SC1100 controller requires 4-byte aligned data transfers and cannot handle transfers of
     exactly 64 kilobytes.

     The CS5530 multifunction chip/core's IDE section claims to be capable of UDMA mode 2
     (33.3MB/s) but in practice using that mode swamps the controller so badly that geodeide lim-
     its the UDMA negotiation to mode 1 (25MB/s) so that the other functions of this chip con-
     tinue to work.

     The IDE DMA engine in the CS5530 can only do transfers on cache-line (16-byte) boundaries.
     Attempts to perform DMA on any other alignment will crash the system.  This problem may also
     exist in the SC1100 since the CS5530 was its direct predecessor, and it is not clear that
     National Semiconductor fixed any bugs in it.

     The geodeide driver will reject attempts to DMA to buffers not aligned to the required
     boundary.	The wd(4) disk driver will back off to PIO mode to accomplish these transfer
     requests, at reduced system performance.

BSD					   July 5, 2005 				      BSD

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