On Sun, Jun 05, 2005 at 09:56:14PM -0400, Timothy Miller wrote:
>
> Yes, of course. We'll have fifos that cross clock domains. In fact,
> that's pretty much the primary way to get data across clock domains.
That puts the purpose into context. When you say "cross clock
domains", are you talking about completely independent clock domains, or
about different clocks that ultimately derive from the same master
oscillator? In other words, do we have to plan for a handshake that can
cope with metastability as in a hard disk interface, or can we design things
so that the receiving register's setup time will always be met?
And with that, I'll hold off taking up any more time in this
discussion until I get further along studying, and have a reasonable chance
of doing some useful work on the project.
On another subject, I did a little preliminary follow-up on the
interest you expressed in having a plug-in option for the memory that holds
the FPGA load image.
Out of half a dozen common flash memory cartridges made for digital
cameras, the only one with a reasonably simple protocol seems to be Memory
Stick. The others emulate ATA interfaces, or floppy disks, or worse. It
has a serial protocol, but not one as simple as the usual serial flash chips
used in embedded systems. It requires a command stream to make it read data
out. A lot is left out of the protocol document I found on line, and there
are hints that an NDA might be required to get the details of the command
syntax.
The other thing to be determined is whether PC-compatible cartridge
reader/writers are readily available, and not just cartridge readers.
Depending on the FPGA card to write the cartridge could very easily create
chicken-and-egg paradoxes, and might well require more hardware.
The sort of implementation I envision is to always install the
regular FPGA image memory EEPROM with hardwired write protection, to
guarantee recovery from an operator goof-up. It would include logic to read
the cartridge, and would automatically load the optional image from there if
the cartridge responded to probing.
Think this is worth further research?
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