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Reclock spi sdcard access after initialisation 

Depends upon https://github.com/enjoy-digital/litex/pull/435

After initialising the card, reclock the card, aiming for ~16MHz (divider is rounded up, as slower speed is safer), but a maximum of half of the processor speed.

Tested with the card being clocked to 12.5MHz on de10nano
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rob-ng15 2020-03-21 07:37:21 +00:00 committed by GitHub
parent f03d862c06
commit 2bf31a31da
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11
litex/soc/software/libbase/spisdcard.c
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@ -444,6 +444,17 @@ uint8_t spi_sdcard_readMBR(void)
return FAILURE;
}
// Reclock the card
// Calculate 16MHz as an integer divider from the CONFIG_CLOCK_FREQUENCY
// Add 1 as will be rounded down
// Always ensure divider is at least 2 - half the processor speed
int divider;
divider = (int)(CONFIG_CLOCK_FREQUENCY/(16e6)) + 1;
if( divider<2 )
divider=2;
printf("Reclocking from %dKHz to %dKHz\n\n", CONFIG_CLOCK_FREQUENCY/(int)spisdcard_clk_divider_read()/1000, CONFIG_CLOCK_FREQUENCY/divider/1000);
spisdcard_clk_divider_write(divider);
// Read in FAT16 File Allocation Table, array of 16bit unsinged integers
// Calculate Storage from TOP of MAIN RAM
sdCardFatTable = (uint16_t *)(MAIN_RAM_BASE+MAIN_RAM_SIZE-sdCardFatBootSector.sector_size*sdCardFatBootSector.fat_size_sectors);