![Linus Torvalds](/assets/img/avatar_default.png)
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!
33 lines
1.7 KiB
Text
33 lines
1.7 KiB
Text
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.
|