path: root/Documentation/arm/Sharp-LH/CompactFlash
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/arm/Sharp-LH/CompactFlash
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+README on the Compact Flash for Card Engines
+There are three challenges in supporting the CF interface of the Card
+Engines. First, every IO operation must be followed with IO to
+another memory region. Second, the slot is wired for one-to-one
+address mapping *and* it is wired for 16 bit access only. Second, the
+interrupt request line from the CF device isn't wired.
+The IOBARRIER issue is covered in README.IOBARRIER. This isn't an
+onerous problem. Enough said here.
+The addressing issue is solved in the
+arch/arm/mach-lh7a40x/ide-lpd7a40x.c file with some awkward
+work-arounds. We implement a special SELECT_DRIVE routine that is
+called before the IDE driver performs its own SELECT_DRIVE. Our code
+recognizes that the SELECT register cannot be modified without also
+writing a command. It send an IDLE_IMMEDIATE command on selecting a
+drive. The function also prevents drive select to the slave drive
+since there can be only one. The awkward part is that the IDE driver,
+even though we have a select procedure, also attempts to change the
+drive by writing directly the SELECT register. This attempt is
+explicitly blocked by the OUTB function--not pretty, but effective.
+The lack of interrupts is a more serious problem. Even though the CF
+card is fast when compared to a normal IDE device, we don't know that
+the CF is really flash. A user could use one of the very small hard
+drives being shipped with a CF interface. The IDE code includes a
+check for interfaces that lack an IRQ. In these cases, submitting a
+command to the IDE controller is followed by a call to poll for
+completion. If the device isn't immediately ready, it schedules a
+timer to poll again later.