Day 9: Pre-Class Self-Check Quiz

Memory: RAM, ROM & Block RAM

Q1: What is the key difference between async ROM read and sync ROM read? Which infers block RAM?

Answer

Asynchronous read: assign o_data = r_mem[i_addr]; (combinational, no latency). Synchronous read: always @(posedge i_clk) o_data <= r_mem[i_addr]; (clocked, 1-cycle latency). Only synchronous read infers block RAM (EBR).

Q2: How much block RAM does the iCE40 HX1K have?

Answer

16 Embedded Block RAM (EBR) blocks × 4 Kbit each = 64 Kbit total (8 KB). Each block configurable as 256×16, 512×8, 1024×4, or 2048×2.

Q3: What system task loads a hex file into a memory array? Where does it work?

Answer

$readmemh("filename.hex", r_mem) loads hexadecimal data. $readmemb loads binary. Both work in simulation (Icarus Verilog) and synthesis (Yosys uses the data for initialization).

Q4: Write the always block for a single-port synchronous RAM with read-before-write behavior.

Answer

always @(posedge i_clk) begin
    if (i_write_en)
        r_mem[i_addr] <= i_write_data;
    o_read_data <= r_mem[i_addr];  // reads old value during write
end