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Diffstat (limited to 'vga-core/vga_address_translator.sv')
| -rw-r--r-- | vga-core/vga_address_translator.sv | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/vga-core/vga_address_translator.sv b/vga-core/vga_address_translator.sv new file mode 100644 index 0000000..cc63fac --- /dev/null +++ b/vga-core/vga_address_translator.sv @@ -0,0 +1,39 @@ +// synopsys translate_off +`timescale 1 ps / 1 ps +// synopsys translate_on + +/* This module converts a user specified coordinates into a memory address. + * The output of the module depends on the resolution set by the user. + */ +module vga_address_translator(x, y, mem_address); + + parameter RESOLUTION = "320x240"; + /* Set this parameter to "160x120" or "320x240". It will cause the VGA adapter to draw each dot on + * the screen by using a block of 4x4 pixels ("160x120" resolution) or 2x2 pixels ("320x240" resolution). + * It effectively reduces the screen resolution to an integer fraction of 640x480. It was necessary + * to reduce the resolution for the Video Memory to fit within the on-chip memory limits. + */ + + input [((RESOLUTION == "320x240") ? (8) : (7)):0] x; + input [((RESOLUTION == "320x240") ? (7) : (6)):0] y; + output reg [((RESOLUTION == "320x240") ? (16) : (14)):0] mem_address; + + /* The basic formula is address = y*WIDTH + x; + * For 320x240 resolution we can write 320 as (256 + 64). Memory address becomes + * (y*256) + (y*64) + x; + * This simplifies multiplication a simple shift and add operation. + * A leading 0 bit is added to each operand to ensure that they are treated as unsigned + * inputs. By default the use a '+' operator will generate a signed adder. + * Similarly, for 160x120 resolution we write 160 as 128+32. + */ + wire [16:0] res_320x240 = ({1'b0, y, 8'd0} + {1'b0, y, 6'd0} + {1'b0, x}); + wire [15:0] res_160x120 = ({1'b0, y, 7'd0} + {1'b0, y, 5'd0} + {1'b0, x}); + + always @(*) + begin + if (RESOLUTION == "320x240") + mem_address = res_320x240; + else + mem_address = res_160x120[14:0]; + end +endmodule |