5 Aug
2005
5 Aug
'05
8:24 a.m.
On 8/5/05, Jim Brain <brain at jbrain.com> wrote:
The IDE command registers are all 8-bits wide, but the
Data register is
16 bits wide. You have to support a 16 bit transfer in order to get the
data from the sector buffer (256 16 bit transfers nets you 512 bytes of
data, the IDE std sector). IN the newer 48 bit addressing mode, the LBA
registers grow from 8 bits to 16 bits as well.
All the IDE code I've looked at does it this way. I believe I have the
ATA r4 spec here that states that as well.
But, if you've noted a way to switch IDE into 8-bit mode, let me know.
This is not an ATA feature I'm talking about, it's a CF feature...
you can switch the Compact Flash card to use only 8-bit transfers, in
case you need to connect the Compact Flash card to an 8-bit bus.
Accessing a drive takes the following steps:
1. The address is asserted on lines A0-A2 and /CS0 + /CS1. In True
IDE mode, only three of the address lines of the Compact Flash card
are used, in combination with the /CS0 and /CS1 lines which select the
"register set". Only either of the /CS0 and /CS1 lines is active (not
both at the same time).
2. After a delay of 70 ns (or more), either the /IORD or /IOWR is
activated, depending on whether you want to initiate a read or write
instruction. The /IORD or /IOWR are the strobes.
3. Another delay, of 165 ns, is needed before inactivating the
/IORD or /IOWR lines. At the same time of inactivating the strobe, or
immediately before or after inactivating the strobe, you can read or
write the data to the D0-D15 lines.
4. Although this is optional, it is recommended that both /CS0 and
/CS1 are inactivated at the end of the read or write cycle. You may
need another delay here, because a full cycle has also a minimal
duration. Instead of a simple idle loop, you may however choose to
perform other operations in that time --such as interpreting the data
after a read operation, or fetching new data after a write operation.
So... again, the problems I'm having are with certain cards and not
others. My records of success are 4MB HP - fail, 16MB Kodak - strange
behavior/fail, 512MB Simple Technology - fail, SanDisk 1GB - works.
I'm just trying to solicit input from anyone who might know a tidbit
like "don't try that with cards under 32MB" or some other such nugget
of wisdom. I brought up the 8-bit mode thing because it's an unusual
use of the CF card and might be relevant.
Thanks,
-ethan