@cabingh I'm not sure about that but check this line where it's defined as 64 bytes. As an example, the configuration of L1 for TinyCore (If I'm right) it's:
D$ cache size = 256 nSets * 1 nWays * 64 CacheBlockbytes = 16384 Bytes = 16 KiB
I$ cache size = 64 nSets * 1 nWays * 64 CacheBlockbytes = 4096 Bytes = 4 KiB
...using the image below (different cfg) we can say that by default we have block size equals to 512-bit (64*8) instead of 32-bit like image.
is this right @aswaterman ?