I think someone here mentioned the possibility to configure an Xilinx Spartan-3E fpga with an SD-Card (MMC) in SPI mode. However when checking on this by chance today I found that it seems to not work because:
FPGA's can get configured from DATAFLASH mounted in SDCARD plastic (atmel sells those!) and sure mmc-sd can be used in spi or sd mode, but there is extra circuitry required, either mcu or cpld
SD card cannot be master, you need to have a Master to get the data from! FPGA CONFIG RAM cannot be master, you need to have a master to write the data to the FPGA RAM !
For programming FPGA, you need a master getting the data from SD and writing to FPGA RAM.
SD card doesnt need to be master, the issue is that it is not compatible to the FPGA command used in master serial mode, etc.
with MMC card (not SD!) a RECONFIGURATION from MMC card could be possible, if
1 S3E is configured from SPI flash
2 S3E puts SPI flash into DEEP powerdown or any other mode that prevents configuration in case of PROG toggle
3 S3E prepares MMC card to enter STREAMING READ (not available on SD cards) mode and pre shifts instruction and address
4 S3E pulses its own PROG pin
5 S3E would be configured from a file located on the MMC card
so while INITIAL load from card is no way possible a repeated secondary configuration can be possible
S3E should be connected properly SPI flash and MMC card pins in parallel, MMC card should be operating in non SPI mode
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