drivers/sdcard: Support old SD cards (<=2GB).

Author: aykevl

drivers/sdcard/sdcard.py

@@ -96,9 +96,14 @@ def init_card(self):
  raise OSError("no response from SD card")
  csd = bytearray(16)
  self.readinto(csd)
- if csd[0] & 0xc0 != 0x40:
+ if csd[0] & 0xc0 == 0x40: # CSD version 2.0
+ self.sectors = ((csd[8] << 8 | csd[9]) + 1) * 2014
+ elif csd[0] & 0xc0 == 0x00: # CSD version 1.0 (old, <=2GB)
+ c_size = csd[6] & 0b11 | csd[7] << 2 | (csd[8] & 0b11000000) << 4
+ c_size_mult = ((csd[9] & 0b11) << 1) | csd[10] >> 7
+ self.sectors = (c_size + 1) * (2 ** (c_size_mult + 2))
+ else:
  raise OSError("SD card CSD format not supported")
- self.sectors = ((csd[8] << 8 | csd[9]) + 1) * 2014
  #print('sectors', self.sectors)
 
  # CMD16: set block length to 512 bytes