16.8 GB/s LPDDR4-3200@32-bit memory access bandwidth

Abstract

Today's In-Vehicle Infotainment system requires more external memory access bandwidth (MABW) [1] especially for high definition (HD) video/audio. It demands maximum utilization for SDRAM access instead of expansion for SDRAM capacity due to limitation of chip size. An LPDDR4-3200 @32-bit SDRAM supports 12.8GB/s [2], and efficiency is limited to around 95% by SDRAM AC timing. An idea to achieve even more MABW than the limitation is introduced. Placing lossless compression unit [3] at source of requests, and decompression unit (DCU) integrated inside memory controller (MC), the number of SDRAM command has been deducted while increasing bus data bandwidth. However, latency becomes a critical issue for real-time request which may be non-decompression while going through DCU with big number of processing cycles. The adaptive solution is applied in this work so that both bandwidth and latency requirement are satisfied. The non-decompression transaction is separated and processed out-of-order to relax the latency, whereas the decompression transaction goes through DCU for decompression processing. Simulation result on LPDDR4-3200 @ 32-bit shows average 16.8 GB/s MABW for data rate after decompression using video playback data stream, with real-time requirement maintaining.