If the target device is transmit and receive, the minimum frequency of ssi_clk is 8 times the maximum expected frequency of the bit-rate clock from the controller device (sclk_in). This minimum frequency is to ensure that data on the controller's rxd line is stable before the controller's shift control logic captures the data. The 8:1 ratio ensures that the target has driven data onto the controller's rxd line three ssi_clk cycles before the data is captured, which is indicated by tc (time before capture) in Figure 2-3.
4.03a 版本
另外,在 SSI_ENH_CLK_RATIO = 1 下,
To reduce the synchronization delay, the synchronization scheme uses two flip flops: one works on the
positive edge of ssi_clk; and other works on the negative edge of ssi_clk. These flip flops reduce the
synchronization delay to one ssi_clk cycle and enable DW_apb_ssi to work on lower clock ratios. W