Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

FIFO output BigEndian or LittleEndian!

hi,when using FIFO of LPM,output width is made different from input width,if I make input[63:0] and output[7:0],the waveform shows that the output starts from the LSB of the input ,ie,[7:0]、...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

The answer is somewhat more complex: the swapping depends on what your 64 bits at the input represent. For a 64 bit packet representing 8 bytes in little-endian we basically have 4 choices in big-endian format:

8 bit words -> the byte order remains -> b0 b1 b2 b3 b4 b5 b6 b7

16 bit words -> swap/reverse every pair -> b1 b0 b3 b2 b5 b4 b7 b6

32 bit words -> swap/reverse every quad -> b3 b2 b1 b0 b7 b6 b5 b4

64 bit words -> reverse all 8 -> b7 b6 b5 b4 b3 b2 b1 b0