FAT FS on an SX?
Phil Pemberton
Posts: 16
Hi,
Has anyone managed to implement the FAT16 filing system (or a subset of it) on an SX?
I'm looking into the prospects of using a MultiMediaCard for data storage on a future project and although it would be OK to save on an MMC with a custom filing system, it would be even cooler if I could implement FAT.
The only problem I can forsee at the moment is the 16 bytes per page limit on file-register RAM on the SX. That would make filename comparisons truly painful (a FAT filename is 8.3 format, i.e. 8-char filename + 3-char extension, so 11 characters).
That said, bankswitching shouldn't slow it down too much (a bankswitch is a single-byte instruction IIRC), it's just that I'd rather like to avoid it if at all possible (speed, speed, speed!). Or have I misunderstood the SX programming model again?
Has anyone managed to implement the FAT16 filing system (or a subset of it) on an SX?
I'm looking into the prospects of using a MultiMediaCard for data storage on a future project and although it would be OK to save on an MMC with a custom filing system, it would be even cooler if I could implement FAT.
The only problem I can forsee at the moment is the 16 bytes per page limit on file-register RAM on the SX. That would make filename comparisons truly painful (a FAT filename is 8.3 format, i.e. 8-char filename + 3-char extension, so 11 characters).
That said, bankswitching shouldn't slow it down too much (a bankswitch is a single-byte instruction IIRC), it's just that I'd rather like to avoid it if at all possible (speed, speed, speed!). Or have I misunderstood the SX programming model again?
Comments
Yes it can be done. I implemented FAT16 in my SD Data logger.
I used an SX48 and an external 32K SRAM chip.
However it is limited to 16 files and·32MB·per media.
They should be available soon if you would like one.
Bean.
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Cheap 4-digit LED display with driver IC·www.hc4led.com
Low power SD Data Logger www.sddatalogger.com
"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh
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I've just been pricing two variants of the circuitry, and it looks like the CPLD version I designed in ISE would work out about $5 cheaper to build, just from replacing the 74HC stuff with an XC95144XL CPLD, and I'd have some spare space in the CPLD for other stuff too.
Only problem is, the thing wolfs down close to 50mA of current, even when it's only running at 16MHz. I shudder to think of what it's going to pull at 50MHz. That said, given another 50mA for the SX and LCD, a 650mAh lithium ion pack should last around six hours. A 2500MAh AA pack should be able to power the thing for just over a day.
I think the biggest problem is going to be finding enough ROM space for the LCD character generator LUT [noparse]:([/noparse]