[Coco] ANNOUNCE: Cloud-9 Website Update

[John Kent]

On 26/08/2011 11:58 AM, Mark McDougall wrote:
>
> Only high-end (usually full frame) DSLR cameras use CF.
>
> CF is still faster than SD due to its parallel bus, which is 
> more-or-less an ATA bus. High-end cameras have larger sensors which 
> require more storage, hence the higher throughput requirement in order 
> to support multi-frames-per-second shooting.
>
> I also believe that embedded PCs tend to include CF slots (as opposed 
> to SD) for booting media from SSD, though that may be because it's 
> easier to interface to existing chipsets?!? FWIW our last product - 
> essentially an embedded PC platform - has CF, CFast (see below) but no 
> SD.
>
> The CF form factor now has a serial bus version, called C-Fast, but I 
> think the jury is still out on that with regards to whether it will 
> make a dent in the market place.
>
> Regards,
>

I use CF cards in True IDE mode simply because the interface is 
relatively simple to understand and they are relatively easy to 
interface. IDE mode is just a matter of setting up the sector address 
and head and so on, issuing a read or write sector command, polling the 
status register and reading or writing the data register. It's not 
unlike reading a floppy disk controller.

You can quite easily get CF to IDE adapter cards which use the standard 
40 pin IDC connector with 0.1" pin spacing which is easier to interface 
to. The IDE registers simply map into the CPU memory space.

To operate CF in true IDE mode, the CF card has to be powered up with 
one of the input pins held low. This means that on a CF IDE interface 
board there should really be a FET switch on the supply rail so that the 
CF card is not powered up unless it has been plugged into the socket. 
Many of the cheaper IDE / CF adapter cards do not have that feature so 
do not support hot change over. i.e. you have to power down the adapter, 
inserting the new CF card then power it up again.

The advantage also of using IDE is that you can also interface to an old 
IDE hard disk. IDE hard disks tend to use 5V logic levels and the I/O 
pins of an FPGA normally operate at 3.3V so to interface to 5V logic you 
have to have series current limiting resistors and the FPGA has to have 
diode clamps on the input pins so as not to damage the FPGA.

I'd use SD cards if I knew a bit more about how the internal registers 
worked. The description of the SD card registers from my reading some 
years ago used register names that I was unfamiliar with and seemed 
complicated than the IDE interface. I couldn't find a good description 
of how they worked. SD cards seemed to support a number of different 
serial protocols such as SPI and I2C and also nybble protocols. You'd 
need some sort of SPI or I2C interface chip to interface to the CoCo, or 
else bit back an I/O port. They'd be a bit slower to talk to but I don't 
think that is a big problem for the CoCo.

The Altera DE1 & DE2 FPGA boards do have a socket for a SD card on the 
board. They also have two parallel expansion sockets, which could be 
used to interface to IDE. The Spartan 3 starter board also has expansion 
connectors that can be used to interface to IDE. The difficulty is that 
you need some sort of adapter board to transposing the pins of the FPGA 
board connector to line up with the IDE connector. Some FPGA boards such 
as the XESS XST-4.0 carrier board do have IDE expansion sockets on them 
which makes it much easy to interface to IDE disks.

To use SATA you need to use a fairly high end FPGA that supports the 
high speed serial rocket (?) I/O. SATA runs at 3 to 6 Gbps. Such FPGAs 
have tended to be outside the price range that I can afford. I believe 
Rocket I/O supports a variety of high speed serial interfaces such as 
SATA, PCIe, GigE, SDI and so on. I'm not sure what is required in terms 
of development software to use Rocket I/O. You can get SATA to IDE 
adapters which might be an easier way to interface a SATA drive to a 
FPGA board or CoCo.

John.

-- 
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