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author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/arm/Sharp-LH/CompactFlash | |
download | lwn-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz lwn-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.zip |
Linux-2.6.12-rc2v2.6.12-rc2
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!
Diffstat (limited to 'Documentation/arm/Sharp-LH/CompactFlash')
-rw-r--r-- | Documentation/arm/Sharp-LH/CompactFlash | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/Documentation/arm/Sharp-LH/CompactFlash b/Documentation/arm/Sharp-LH/CompactFlash new file mode 100644 index 000000000000..8616d877df9e --- /dev/null +++ b/Documentation/arm/Sharp-LH/CompactFlash @@ -0,0 +1,32 @@ +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. |