This warning only occurs near the beginning of the decoded trace when the trace buffer (not the FIFO) of the TPA has overflowed. It means that there has not yet been a complete memory access address in the trace data, and therefore the trace decoder cannot calculate the address of a data access. The ETM outputs a complete address on the first data access traced, and repeats this every 1024 cycles after this, if there are data accesses to be traced. To reduce buffer usage, other memory addresses are output relative to the last full memory address. If the buffer overflows, and the complete address is lost, the decoder cannot calculate data addresses that occur before the next full data address is emitted.