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Based on kernel version 2.6.38. Page generated on 2011-03-22 22:18 EST.

1	README on the Compact Flash for Card Engines
2	============================================
3	
4	There are three challenges in supporting the CF interface of the Card
5	Engines.  First, every IO operation must be followed with IO to
6	another memory region.  Second, the slot is wired for one-to-one
7	address mapping *and* it is wired for 16 bit access only.  Second, the
8	interrupt request line from the CF device isn't wired.
9	
10	The IOBARRIER issue is covered in README.IOBARRIER.  This isn't an
11	onerous problem.  Enough said here.
12	
13	The addressing issue is solved in the
14	arch/arm/mach-lh7a40x/ide-lpd7a40x.c file with some awkward
15	work-arounds.  We implement a special SELECT_DRIVE routine that is
16	called before the IDE driver performs its own SELECT_DRIVE.  Our code
17	recognizes that the SELECT register cannot be modified without also
18	writing a command.  It send an IDLE_IMMEDIATE command on selecting a
19	drive.  The function also prevents drive select to the slave drive
20	since there can be only one.  The awkward part is that the IDE driver,
21	even though we have a select procedure, also attempts to change the
22	drive by writing directly the SELECT register.  This attempt is
23	explicitly blocked by the OUTB function--not pretty, but effective.
24	
25	The lack of interrupts is a more serious problem.  Even though the CF
26	card is fast when compared to a normal IDE device, we don't know that
27	the CF is really flash.  A user could use one of the very small hard
28	drives being shipped with a CF interface.  The IDE code includes a
29	check for interfaces that lack an IRQ.  In these cases, submitting a
30	command to the IDE controller is followed by a call to poll for
31	completion.  If the device isn't immediately ready, it schedules a
32	timer to poll again later.
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