4 Dec
2010
4 Dec
'10
7:33 p.m.
SD cards are attractive in many ways. For one thing,
they can be
accessed via an SPI interface which saves some I/O pins on that end.
Since I really know nothing about SCSI, I don't know if that is a good
approach for a SCSI/SD adapter or not. I wonder if there are any real
time requirements in a SCSI interface that would be impacted by talking
to the SD card in a bit serial fashion.
As far as I know, there is nothing in the SCSI spec that specifies a
minimum data rate or a maximum seek time. Soyou could even read 1 byte
out of an SD card and then send it over the SCSI interfce, and then do
the net byte, and so on. It would probably be better to buffer a 'sector'
in RAM on the microcontroller, and then transfer the buffer to the SCSI
interface.
However, it's entirely possible that some OSes will moan if the device is
too slow because they will assuem there's a hardware failure. However, I
would think the time taken to read/write a 'sector' from an SD card would
nopt be any longer than the seek time of some hard drives. So there
should be no problem.
-tony