1.什么是FPGA的专用SPI接口？
此处的SPI FLASH接口即为FPGA的专用SPI接口，上电时，FPGA从该FLASH读出程序并运行。
2.访问SPI PROM需要注意哪些地方？
1）处于MASTER SPI MODE
2）调用USRMCLK原语，使用时序逻辑配置USRMCLKTS,
上电过程中先是高，然后PLL的lock锁定后几个时钟再把这个信号拉低。
3）将CONEIG IOVOLTAGE设置为3.3
3.USRMCLK原语说明
查看数据手册<<ECP5 and ECP5-5G sysCONFIG User Guide>>可知，通过调用原语USRMCLK
将切换SPI接口的MCLK引脚时钟源。
module top(//System interface input rst_n,input sys_clk,//Flash interface input spi_miso,output spi_mosi,output spi_cs_n );wire clk_flash;wire pll_locked;reg pll_locked_ff1;reg pll_locked_ff2;reg spi_clk_en;pll_sys u_pll_sys(.CLKI(sys_clk), //50M.CLKOP(clk_flash), //20M.LOCK(pll_locked) );always @(posedge clk_flash or negedge pll_locked)beginif(!pll_locked)beginpll_locked_ff1 <= 1'd0;pll_locked_ff2 <= 1'd0;endelse beginpll_locked_ff1 <= pll_locked;pll_locked_ff2 <= pll_locked_ff1;endendalways @(posedge clk_flash or negedge pll_locked)beginif(!pll_locked)spi_clk_en <= 1'd1;else if(pll_locked_ff2)spi_clk_en <= 1'd0;else;endUSRMCLK u_USRMCLK(.USRMCLKI(spi_clk),.USRMCLKTS(spi_clk_en) ) /* synthesis syn_noprune=1 */;flash_drive flash_drive_u0(.i_clk (clk_flash ),.i_rst (~rst_n ),.i_operation_type (w_operation_type ),.i_operation_addr (w_operation_addr ),.i_operation_num (w_operation_num ),.i_operation_valid (w_operation_valid ),.o_operation_ready (w_operation_ready ),.i_write_data (w_write_data ),.i_write_sop (w_write_sop ),.i_write_eop (w_write_eop ),.i_write_valid (w_write_valid ),.o_read_data (w_read_data ),.o_read_sop (w_read_sop ),.o_read_eop (w_read_eop ),.o_read_valid (w_read_valid ),.o_spi_clk (spi_clk ),.o_spi_cs (o_spi_cs_n ),.o_spi_mosi (o_spi_mosi ),.i_spi_miso (i_spi_miso )
);endmodule4.CONFIG IOVOLTAGE设置
