初始化SD卡 Reset: mrs r0, CPSR bic r0, r0, #0x1f orr r0, r0, #0xd3 msr CPSR_fc, r0 -init SD card Reset: mrs r0, CPSR bic r0, r0,#0x1f orr r0, r0,#0xd3 msr CPSR_fc, r0