SD vs SDHC

[alank2]

For those of you who have worked with SD/SDHC, what do you have to do different for a SDHC as far as the interface/communication protocol is concerned?

[exmadscientist]

SDHC is little different from plain SD, as long as you have FAT32 support (which you probably do). The main change is that the initialization sequence is slightly different, accounting for the different representation used for card space.

SDXC is when things start to get more troublesome, as it brings mandatory exFAT support into the picture.

[NiHaoMike]

SDXC is when things start to get more troublesome, as it brings mandatory exFAT support into the picture.

You could reformat the card to FAT32 or some better filesystem like ext4.

[exmadscientist]

SDXC is when things start to get more troublesome, as it brings mandatory exFAT support into the picture.

You could reformat the card to FAT32 or some better filesystem like ext4.

Sure, but if you do that, then you've got an oddball card that doesn't actually comply with the SDXC spec, which mandates exFAT. You probably won't be able to read it in anything but your device (and, probably, a Linux box). That's all good and well for a one-off or personal project, but users will hate it -- and rightfully so.

[Berni]

Just a slight difference in initialization to let you know the card is SDHC because they use sector addressing rather than byte addressing. This tweak lets them address 512 times more memory.

Most modern FAT32 libraries that support SD also automagically support SDHC

[voltsandjolts]

It is disappointing to see the SD Card Association mandate exFat for SDXC which is yet another propriety and patented Microsoft file system.
Why could they not have used an open standard free for all to use, helping all consumers who use SD cards. Instead they choose to be part of the tech extortion cartel which puts toll gates in the path of interoperability.

[Kilrah]

It is disappointing to see the SD Card Association mandate exFat for SDXC which is yet another propriety and patented Microsoft file system.
Why could they not have used an open standard free for all to use

Name an open and widely implemented format that allows for those sizes and doesn't have a 4GB filesize limit? Oh, right...

[voltsandjolts]

Name an open and widely implemented format that allows for those sizes and doesn't have a 4GB filesize limit? Oh, right...

Well, there is f2fs or ext2 which are both open standards and suitable for flash storage.
But my point is, if existing standards did not suit them, the SD Card Association could have developed their own open standard for SDXC and actively helped consumer product interoperability. Instead they chose to use exFat which was designed to be patented and extract royalties, not to be technically novel or move technology forward in any meaningful sense.

[Kilrah]

Well, there is f2fs or ext2 which are both open standards and suitable for flash storage.

Neither of those are properly supported on the Windows computers that 95% of SD card users are going to use to read them.

But my point is, if existing standards did not suit them, the SD Card Association could have developed their own open standard for SDXC and actively helped consumer product interoperability. Instead they chose to use exFat which was designed to be patented and extract royalties

But the SD Card Association's own purpose is precisely to market patents and extract royalties!

These associations are created by the big technology companies precisely as joint ventures to market their respective technologies. Someone did R&D to develop a card format, someone did R&D to develop memory that can fit in there, someone did R&D to develop a file format that's suitable and easy to implement for said companies and the customers etc... put that all together, market it, and share the profits to recoup the investments.

[voltsandjolts]

Neither of those are properly supported on the Windows computers that 95% of SD card users are going to use to read them.

And neither was exFat before it was 'invented' and pushed down our throats via Windows Update. Any new open format could have been delivered in the same way and in fact could have seen much wider adoption (by virtue of being open).

But the SD Card Association's own purpose is precisely to market patents and extract royalties!

And I'm fine with that, as long as it's related to the hardware of the device. That's what I pay for when I buy a physical SDXC card. Maybe if they had been more helpful and used an open file system format they would sell more SD cards.

Someone did R&D to develop a card format

Probably two people - a lawyer and an accountant.

[Kilrah]

And neither was exFat before it was 'invented' and pushed down our throats via Windows Update. Any new open format could have been delivered in the same way and in fact could have seen much wider adoption (by virtue of being open).

exFAT existed 3 years before SDXC cards were announced. Why would you work on / develop support for an open standard when you've got something appropriate that's there, and fits the commercial goals?

Maybe if they had been more helpful and used an open file system format they would sell more SD cards.

Pretty much everything that has a use for exFAT already supports it and has for quite a while. Someone who needs it for a commercial product can afford the licence with no problem, they already have to pay for one for the use of SD in the first place anyway.
The only ones who might have trouble are hobbyists, and of course they don't care the slightest about those, it's insignificant.

[voltsandjolts]

exFAT existed 3 years before SDXC cards were announced

Hah, of course it did, Microsoft getting ready to sell it's wares!   

Someone who needs it for a commercial product can afford the licence with no problem

And who pays for that, the consumer of course 

And then you pay for the app to get exFat on your phone, then your SDXC doesn't work in your NAS...all a PITA because of a file system that has less merit than many free and open solutions.

It would just be nice to buy an SDXC card that works interoperably across all my devices - that's what SD should be about, not just a memory stick for Windows.

[bson]

The only ones who might have trouble are hobbyists, and of course they don't care the slightest about those, it's insignificant.

I doubt hobbyists have any problems.  If you implement an open-source exFAT and put it up on github for instance there's no problem - you just can't sell products with it.  You can use it to your hearts content for your own purposes, or with friends, or the good people here at eevblog or elsewhere.  As long as you don't try to sell it there's no problem.  And if you do decide to sell it... just go license the rights.  It's no big deal any which way.

My main beef with SDXC is that there's no single patent pool that can be licensed using uniform boilerplate terms, unlike say MPEG LA.  Instead you need to figure out on your own all the random little things you need to license, then negotiate with each of the owners individually.  Miss something and you're now in the position of negotiating a posteriori which weakens your position.

[Kilrah]

I doubt hobbyists have any problems.  If you implement an open-source exFAT and put it up on github for instance there's no problem

Sure, what I meant was that as far as I knew an open source implementation didn't exist, so if you wanted to use exFAT in your microcontroller or FPGA-based gizmo you might have been in for a wild ride reverse-engineering and implementing it.

But a quick search shows that there's already an implementation coming from Samsung (which I assume works, since my Samsung things are perfectly happy with exFAT media ) so it's all a matter of wrapping it properly, no issue.
https://github.com/dorimanx/exfat-nofuse

[voltsandjolts]

I doubt hobbyists have any problems.

Sure, I just wish everybody could use it without problems.
If the cost of driver development was factored into the actual hardware cost of the SDXC card and thus a reference driver implementation made openly available, interoperability for the consumer would be much improved.

[NiHaoMike]

Licensing issues aside, I also remember reading that at least on Raspberry Pi, exFAT is significantly slower than ext4.

Maybe a workaround is to ship the product without the driver, then have the user download it during setup? But I suggest simply refusing to support such garbage if you can get away with it.

BTW, Android 6.0 devices have the option to reformat the SD card with ext4 in order to allow installing apps on it. Something to do with the file permissions, which neither FAT32 nor exFAT support to the required degree.

[David Hess]

It is disappointing to see the SD Card Association mandate exFat for SDXC which is yet another propriety and patented Microsoft file system.
Why could they not have used an open standard free for all to use

Name an open and widely implemented format that allows for those sizes and doesn't have a 4GB filesize limit? Oh, right...

UDF

But as pointed out above, no royalty free standard was going to be approved with Microsoft calling the shots even if they had to invent a new filesystem.  If UDF had been used, Microsoft would have made sure Windows did not support it on removable media.

As far as Windows compatibility, with Microsoft's continuing Windows 10 screw ups that is becoming less important as time goes on.

[voltsandjolts]

Well, stone the crows.
Microsoft is making exFAT available for use in the Linux kernel.
https://www.zdnet.com/article/microsoft-readies-exfat-patents-for-linux-and-open-source/