Improved stimuli using generics and functions to define the write and read block accesses. Distinghuis between tests for DDR3 and DDR4, because DDR4 model simulates about 20x slower.

Added g_sim, when TRUE then use internal DDR memory model in tech_ddr component. When FALSE use DDR memory model in test bench.

Only need to reset the state reg, do not reset the other signals to easy timing closure. Use natural for burst_wr_cnt instead of slv.

Define t_mem_ctlr_mosi/miso in common_mem_pkg, to use that instead of the records defined in tech_ddr_pkg. Also remove t_tech_ddr_addr record because it is not needed.

Check UNSIGNED(wr_fifo_usedw) < c_dp_factor, because a mixed width FIFO cannot always be flushed completely empty, which is ok.diff

Use ctlr slv address instead of record address. Separate p_burst_size into wr and rd process and define burstsize as positive. Assign ctlr_mosi.burstsize directly using wr/rd_burst_size, no need for ctlr_mosi_burstsize.

Added io_ddr_cross_domain.vhd to handle dvr_clk and ctlr_clk domains in case they are different clock domains.