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| MMC on SPI https://www.8devices.com/community/viewtopic.php?f=22&t=1013 |
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| Author: | iggarpe [ 27 Mar 2017, 02:02 ] |
| Post subject: | MMC on SPI |
I need some large storage and the 128M internal flash won't cut it, so I've been trying to connect an SD/MMC card in SPI mode. I figured I'd share my progress. This is what is needed: - Level translation: SD cards work with 3.3V, Rambutan GPIO is 2.5V. I'm using a TXB0108. - Tiny patch to mach-rambutan.c. - Install mmc and mmc_spi kernel modules. So far: - The level translator needs to be disabled or board won't boot. I think it's attempting to boot from external SPI flash. I'll figure out what's going on later. - The fastest SPI clock seems to be ~7MHz. - The SPI driver does not use DMA and/or uses a busy wait, which sort of freezes the system during disk I/O. The later is a deal breaker for me. Suggestions welcome. |
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| Author: | anotherfiz [ 28 Mar 2017, 12:41 ] |
| Post subject: | Re: MMC on SPI |
Any chance you can post your schematic with your fix / your process? I'm interested in doing something similar and ran into problems booting as well, after connecting the SD card. I first tried with a 16MB NOR chip and had no issues. |
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| Author: | iggarpe [ 07 Apr 2017, 12:20 ] | ||
| Post subject: | Re: MMC on SPI | ||
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| Author: | iggarpe [ 07 Apr 2017, 12:27 ] |
| Post subject: | Re: MMC on SPI |
Also, just for the record, since I do need large storage in my project, I ended up adding an USB2640 + microSD card to my design. Costly but gives me also an extra USB port. If anyone finds a way to use the mmc_spi driver without those freezes I'll be happy to go back to microSD on SPI bus (although to be hones I'd rather go with one of the new 4Gb NAND serial flash, but kernel drivers aren't available yet). |
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