| 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. |
