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.