CCS/EK-TM4C129EXL: SPI Data-sending format

Typically when we talk of little endian vs big endian, we are talking about byte order, but I believe your question is about bit order. If I understand your request correctly, you receive data on the SSI in one format (i.e. for data 0x7f - 0111 1111) and need to send it out in the reverse order (i.e. 0xfe - 1111 1110) . There is no hardware function to change the bit order in the SSI. This needs to be done in software. A fast way to flip the bit order of a byte is to use a lookup table of 256 bytes stored in the flash.

Here is an example of a table and function to reverse the bit order of a byte:

const unsigned char reverseBitTable[256] =
{
        0x00,   0x80,   0x40,   0xc0,   0x20,   0xa0,   0x60,   0xe0,
        0x10,   0x90,   0x50,   0xd0,   0x30,   0xb0,   0x70,   0xf0,
        0x08,   0x88,   0x48,   0xc8,   0x28,   0xa8,   0x68,   0xe8,
        0x18,   0x98,   0x58,   0xd8,   0x38,   0xb8,   0x78,   0xf8,
        0x04,   0x84,   0x44,   0xc4,   0x24,   0xa4,   0x64,   0xe4,
        0x14,   0x94,   0x54,   0xd4,   0x34,   0xb4,   0x74,   0xf4,
        0x0c,   0x8c,   0x4c,   0xcc,   0x2c,   0xac,   0x6c,   0xec,
        0x1c,   0x9c,   0x5c,   0xdc,   0x3c,   0xbc,   0x7c,   0xfc,
        0x02,   0x82,   0x42,   0xc2,   0x22,   0xa2,   0x62,   0xe2,
        0x12,   0x92,   0x52,   0xd2,   0x32,   0xb2,   0x72,   0xf2,
        0x0a,   0x8a,   0x4a,   0xca,   0x2a,   0xaa,   0x6a,   0xea,
        0x1a,   0x9a,   0x5a,   0xda,   0x3a,   0xba,   0x7a,   0xfa,
        0x06,   0x86,   0x46,   0xc6,   0x26,   0xa6,   0x66,   0xe6,
        0x16,   0x96,   0x56,   0xd6,   0x36,   0xb6,   0x76,   0xf6,
        0x0e,   0x8e,   0x4e,   0xce,   0x2e,   0xae,   0x6e,   0xee,
        0x1e,   0x9e,   0x5e,   0xde,   0x3e,   0xbe,   0x7e,   0xfe,
        0x01,   0x81,   0x41,   0xc1,   0x21,   0xa1,   0x61,   0xe1,
        0x11,   0x91,   0x51,   0xd1,   0x31,   0xb1,   0x71,   0xf1,
        0x09,   0x89,   0x49,   0xc9,   0x29,   0xa9,   0x69,   0xe9,
        0x19,   0x99,   0x59,   0xd9,   0x39,   0xb9,   0x79,   0xf9,
        0x05,   0x85,   0x45,   0xc5,   0x25,   0xa5,   0x65,   0xe5,
        0x15,   0x95,   0x55,   0xd5,   0x35,   0xb5,   0x75,   0xf5,
        0x0d,   0x8d,   0x4d,   0xcd,   0x2d,   0xad,   0x6d,   0xed,
        0x1d,   0x9d,   0x5d,   0xdd,   0x3d,   0xbd,   0x7d,   0xfd,
        0x03,   0x83,   0x43,   0xc3,   0x23,   0xa3,   0x63,   0xe3,
        0x13,   0x93,   0x53,   0xd3,   0x33,   0xb3,   0x73,   0xf3,
        0x0b,   0x8b,   0x4b,   0xcb,   0x2b,   0xab,   0x6b,   0xeb,
        0x1b,   0x9b,   0x5b,   0xdb,   0x3b,   0xbb,   0x7b,   0xfb,
        0x07,   0x87,   0x47,   0xc7,   0x27,   0xa7,   0x67,   0xe7,
        0x17,   0x97,   0x57,   0xd7,   0x37,   0xb7,   0x77,   0xf7,
        0x0f,   0x8f,   0x4f,   0xcf,   0x2f,   0xaf,   0x6f,   0xef,
        0x1f,   0x9f,   0x5f,   0xdf,   0x3f,   0xbf,   0x7f,   0xff
};

unsigned char reverseBitOrder(unsigned char in)
{
	return reverseBitTable[in];
}

int
main(void)
{
	return reverseBitOrder(0x0f);
}