Re: CompactFlash and HD unhappy together on the same IDE channel

[Malcolm Gillies <linux-ide@ouabain.org>]

Mark Lord wrote:
> Malcolm Gillies wrote:
>> By swapping around components, I've established that the problem is 
>> unlikely due to the cable (which is 50cm long 80-wire), hard disk or 
>> controller. When I swap to another, slower CF card (one that only 
>> supports PIO rather than MWDMA), the error goes away and the hard disk 
>> operates happily at UDMA/33.
> ..
>> ata1.00: CFA: SanDisk SDCFH-1024, HDX 4.07, max MWDMA2
>> ata1.00: 2001888 sectors, multi 0: LBA
>> ata1.01: ATA-7: SAMSUNG HD400LD, WQ100-14, max UDMA/100
>> ata1.01: 781422768 sectors, multi 0: LBA48
>> ata1.01: limited to UDMA/33 due to 40-wire cable
>> ata1.00: configured for MWDMA2
>> ata1.01: configured for UDMA/33
> ..
> The fastest DMA speed reported for the CF is MWDMA2, which is considerably
> slower than UDMA/33.  When two devices share a cable, normally both must be
> limited to the speed of the slower device, which is MWDMA2 in this case.
> 
> Both devices report being capable of 120ns cycle times for DMA,
> but UDMA double-clocks those cycles, something that is incompatible
> with non-UDMA devices.
> 
> I don't think we can safely assume that UDMA can co-operate with non-UDMA
> on the same cable.  In this case, it might be causing the CF device to 
> falsely detect control cycles.

The mystery for me is that

1) there are no errors reported for the CF device, only for the UDMA HD
2) the HD runs error-free at UDMA/33 when I use a different, PIO-only CF 
card but otherwise the same cabling, adaptor etc.

In response to Alan's suggestion, the second point suggests it's not a 
cabling problem.

Any suggestions on how to debug this further appreciated.

cheers,

Malcolm