Question about reading and writing data with sd card

[SWAT]

1. SCIF in SH4 doesn't support hardware SPI mode, this support only SCI (second serial), but this port of SH4 is muted on the motherboard and is not output outside as SCIF. So on SCIF it's works as bit-bang SPI (software emulated). Using CRC is not necessary. In DS core it is used, in iso loader it's disabled to save memory and speed up.

2. Depends on the data used, if it is already in the cache, then this makes no sense and will take extra time. It is not necessary to use.

3. Depends on the SD card class I think, this is a delay for bit-bang, because it is emulation of SPI not a hardware. But usually this delay is generated by the bit-bang itself and it's enough for most cases.

4. Because DS is shutting down if you execute another binary. And you rewrite some memory with DS core. So it's not possible to return. You need write a command or module for DS if you want save DS core and execute own programs.


And yes, not all SD cards support SPI mode. Also small cards are very slow, maybe need more delays for SPI emulation.