8 Dec
2006
8 Dec
'06
4:46 a.m.
Jules Richardson wrote:
Maybe; but it's not vital to operation as the
intention would be for the
primary storage to be something like a CF card or a USB stick. Although
that is interesting; the primary store is a USB stick then it's
presumably easy to code the firmware so that the device can be plugged
in via a cable to a system running suitable host software as an
alternative (providing the device holds sufficient local memory to
buffer a track and USB data transfer to the host is
fast enough to not upset whatever the floppy emulator's plugged in to).
Unfortunately that's not true :-(. USB is a horrible standard, and it's
not orthogonal - hosts are hosts, and targets (my word, I can't remember
what the official word is) are targets.
So, if your device wants to be able to use USB memory sticks, it needs to
implement the USB host interface. That means it won't be able to talk to
a computer (also a host interface.)
If you want to do both, you'll need two interfaces (and strictly speaking
two sockets - the flat socket (Type A IIRC) should only be implemented on
a host, a target should only have the square Type B socket. It ought to
be impossible to get a flat-4 male to flat-4 male USB cable, apart from
anything else.) (By 'Flat 4' I mean the 'normal' USB socket people see on
their computers. By 'Square', I mean the square one with two bevelled
corners that you don't see as often (an awful lot of USB devices having
captive cables.)
You can probably find a driver chip that will implement both host and
target though, or you may need two driver chips. The Philips PDIUSBD12
(again, IIRC that's the correct name) which is the only one I've ever used
will only do target mode, IIRC.
Firewire is a much nicer standard for this sort of thing, but of course
defeats the object because noone makes Firewire memory sticks :-).
Anyway, I'd definitely stick to CompactFlash, but make sure you implement
a Type-II (IIRC, again!) interface, the physical size of which is slightly
chunkier; that allows you to use the Microdrive harddisks as well as
Flash cards. (To sort of answer one of your other questions, I regularly
use 4GB CompactFlash hard disks in my digital camera - the only downside
of them is they are sloooooooow, at least the cheapo ones I use. It used
to be the cheapest way to get a 4GB compact flash hard disk was buy an
iPod Mini, crack the thing open and steal the hard disk out of it - they
use a CFlash disk internally!)
Cheers,
Tim
--
Tim Walls at home in Leeds
EMail & MSN: tim.walls at snowgoons.com