This article gives more details about this issue: http://electrosofts.com/systemverilog/arrays.html, especially section 5.2. A packed array is a mechanism for subdividing a vector into subfields which can be conveniently accessed as array elements. Consequently, a packed array is guaranteed to be represented as a contiguous set of bits. An unpacked array may or may not be … Read more
Description and examples can be found in IEEE Std 1800-2017 § 11.5.1 “Vector bit-select and part-select addressing”. First IEEE appearance is IEEE 1364-2001 (Verilog) § 4.2.1 “Vector bit-select and part-select addressing”. Here is an direct example from the LRM: logic [31: 0] a_vect; logic [0 :31] b_vect; logic [63: 0] dword; integer sel; a_vect[ 0 … Read more
always is the main type of process from Verilog, the other is an initial which is ran once at the start of a simulation. always_ff @(posedge clk) : Represents a flip-flop (ff), the process is triggered (executed) on every positive edge of the clock. This replaces always @(posedge clk). always_ff @(posedge clk) begin a <= … Read more
Verilog thinks in bits, so reg [7:0] a[0:3] will give you a 4×8 bit array (=4×1 byte array). You get the first byte out of this with a[0]. The third bit of the 2nd byte is a[1][2]. For a 2D array of bytes, first check your simulator/compiler. Older versions (pre ’01, I believe) won’t support … Read more
Some data types in Verilog, such as reg, are 4-state. This means that each bit can be one of 4 values: 0,1,x,z. With the “case equality” operator, ===, x’s are compared, and the result is 1. With ==, the result of the comparison is not 0, as you stated; rather, the result is x, according … Read more
The curly braces mean concatenation, from most significant bit (MSB) on the left down to the least significant bit (LSB) on the right. You are creating a 32-bit bus (result) whose 16 most significant bits consist of 16 copies of bit 15 (the MSB) of the a bus, and whose 16 least significant bits consist … Read more
reg and wire specify how the object will be assigned and are therefore only meaningful for outputs. If you plan to assign your output in sequential code,such as within an always block, declare it as a reg (which really is a misnomer for “variable” in Verilog). Otherwise, it should be a wire, which is also … Read more