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Forum Index : Microcontroller and PC projects : CMM2_G2 - SD card support....
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Hi all.  The manual says the CMM2 will work with cards up to 128GB, but makes no mention of lower-capacity cards, other then to suggest you should use 8GB in FAT32. Is there some technical reason why smaller cards generally WON'T work in the CMM2? I have a large collection of old SD card from 16MB(yes, MB!) upwards. The smallest card I can find that works, is a 1GB Kingston. Why? The CMM2 does not exactly NEED a lot of storage space, nor does it really NEED super-speed SD data transfer rates, so I am just curious why the smaller cards flatly refuse to be seen by the CMM2, and one card I tried(128MB) actually crashed the unit totally, requiring a reset press.  Again - why? Is it as simple as the clock speed for the SD card is too fast for these older lower-capacity cards? If I start to ship units next year complete with a copy of the "Welcome tape", these smaller capacity cards would be PERFECT for that, as it is only 11MB or so all up(the welcome tape thing). Having to use 4GB or 8GB cards for 11MB of demo seems a bit nuts. Hopefully, you can all see what I am getting at. Also, low-capacity cards are also fantastic for logging purposes, as again, you don't need a lot of space for that kind of thing. Smoke makes things work. When the smoke gets out, it stops! |
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phil99 Guru  Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
Standard SD is everything up to 2GB, SD-HC is 4GB to 32GB and SD-XC is 64GB and above. If 1GB works then I would expect smaller cards should also. I use a 256MB on PicoMites without problems. Edit Perhaps try formatting with different settings. The 256MB one is FAT, 16kB allocation unit size. Edited 2023-12-15 14:37 by phil99 |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Good idea - I will try formatting one of the 256MB ones to FAT32. It is FAT by default for that size, so you might be onto something there! I'll keep the thread updated. EDIT: No joy. "SD card not found." That was with a 256MB card formatted to FAT32. Edited 2023-12-15 14:54 by Grogster Smoke makes things work. When the smoke gets out, it stops! |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hi Grogster, All, It is most likely the `MODE' that the SD is being read-from/written-to. There are SD mode and SPI mode, I think old SD mode cards are not supported on CMM2 (or mites in general) as they are designed to use SPI mode. (Maybe I have the terminology back to front but I think you get my gist) Regards, Mick (The Big one) . Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4238 |
Speed? The cmm2 may assume the card to be clocked at x Mhz.? Volhout PicomiteVGA PETSCII ROBOTS |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6792 |
The manual recommends a minimum size of 8GB formatted with FAT32 because small cards may be unreliable. Just why, I don't know. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Hmmmmmmm. Curious, though, isn't it? Apart from being slower, the older smaller cards are no less reliable in my experience. And as I mentioned, speed is not really a concern with SD cards on the CMM2. Perhaps if Peter sees this thread, he will offer some technical details. Volhout and I seem to be thinking the same thing.  I personally think that the clock-speed for the SD card is simply too fast for the older small-capacity cards, which are expecting a slower clock. Newer higher-capacity cards will be able to handle a faster clock. MHOO. Smoke makes things work. When the smoke gets out, it stops! |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6792 |
SD cards are too clever by far. :) There's probably more processing power on one of the newer ones (not just memory space) than there was on some 8-bit computers. There could be timing problems. Peter had trouble with the SD card interface on the PicoMite, if you remember, and ended up switching whatever pins it was on into digital IO mode and bitbanging it rather than use a hardware SPI. I don't know how it's done on the CMM2. I wonder if the old cards put even heavier spikes on the supply rails? Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Mmmmmmm - perhaps you're right. Who knows. I can confirm that ALL the CMM2's I've ever built, are perfectly happy with the larger capacity cards. I use a 4GB card for my testing, and the CMM2 never fails to see that, so as you say.... Ah well. It would have just been a nice way to use up those older cards, but it is what it is, so if I do go ahead and include the welcome tape thing for new CMM2 units from next year, I will just have to buy some SD card - but was hoping I would not have to do that, cos I have a heap of the small capacity ones! Smoke makes things work. When the smoke gets out, it stops! |
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