Today’s embedded systems require high external memory bandwidth to achieve fast boot time and application loading time with minimal cost. Historically, applications such as automotive graphics, industrial systems, digital still cameras, printers, and consumer electronics have used parallel interface memories to reach that goal. Today, low-pin-count serial interfaces like the Serial Peripheral Interface (SPI) are making inroads into applications as a standard memory interface. Major systems-on-chip (SoCs) support SPI as a default configuration not only for small density memories to store configuration parameters, but also for large density memories to store application code.
However, SPI has recently increased in complexity to achieve higher bandwidth. The bus has become wider—x1/x2/x4/x8—and the data rate has expanded from single data rate (SDR) to double data rate (DDR) with frequencies above 100 MHz. The new HyperBus interface, which can also be considered as an 8-bit I/O bus DDR serial interface, has already been integrated into SoCs.