A two-level test data compression technique is presented to reduce both the test data and the test time for System on a Chip (SOC). The level one compression is achieved by Huffman coding for the entire SOC. The level two compression is achieved by broadcasting test patterns to multiple cores simultaneously. Experiments on the d695 benchmark SOC show that the test data and test time are reduced by 64% and 35%, respectively. This technique requires no change of cores and hence provides a feasible SOC test compaction solution for the SOC integrators.