unsigned int bufSize = 1;
volatile unsigned int mailbuffer[256] __attribute__ ((aligned (16)));

unsigned int deviceId = 0x00000000; // SD Card
unsigned int state = 3; // 11b (On, Wait)

mailbuffer[bufSize++] = 0;          // 1. Request indicator
mailbuffer[bufSize++] = 0x00020001; // 2. TAG - Set Power
mailbuffer[bufSize++] = 8;          // 3. Value buffer size (in bytes)
mailbuffer[bufSize++] = deviceId;   // 4. Value - Device id
mailbuffer[bufSize++] = state;      // 5. Value - State
mailbuffer[bufSize++] = 0;          // 6. Response - Device Id
mailbuffer[bufSize++] = 0;          // 7. Response - State
mailbuffer[bufSize++] = 0;          // 8. End of message tag
mailbuffer[0] = bufSize * 4;       // Size of this buffer (in bytes)

====== Response ========
[0] = 36
[1] = 0x80000000
[2] = 0x00020001
[3] = 8
[4] = -2147483640
[5] = 3
[6] = 1
[7] = 0
[8] = 0