WIP ppu fg sprite fetch logic

1 files changed, 20 insertions, 3 deletions

diff --git a/basys3/basys3.srcs/ppu_consts.vhd b/basys3/basys3.srcs/ppu_consts.vhd
index 722954d..75b6168 100644
--- a/basys3/basys3.srcs/ppu_consts.vhd
+++ b/basys3/basys3.srcs/ppu_consts.vhd
@@ -1,12 +1,18 @@
+library ieee;
+use ieee.math_real.all;
+
 -- https://docs.google.com/spreadsheets/d/1MU6K4c4PtMR_JXIpc3I0ZJdLZNnoFO7G2P3olCz6LSc
 package ppu_consts is
+	-- utility functions
+	function ceil_log2(n : natural) return natural;
+
 	constant PPU_RAM_BUS_ADDR_WIDTH : natural := 16; -- RAM bus address width
 	constant PPU_RAM_BUS_DATA_WIDTH : natural := 16; -- RAM bus data width
 	constant PPU_FG_SPRITE_COUNT : natural := 128; -- foreground sprites
 	constant PPU_COLOR_OUTPUT_DEPTH : natural := 4; -- VGA output channel depth
 	constant PPU_PALETTE_COLOR_WIDTH : natural := 3; -- palette index width (within sprite)
 	constant PPU_PALETTE_INDEX_WIDTH : natural := 3; -- palette index width (palette table)
-	constant PPU_PALETTE_CIDX_WIDTH : natural := PPU_PALETTE_COLOR_WIDTH + PPU_PALETTE_INDEX_WIDTH; -- global palette index width
+	constant PPU_PALETTE_CIDX_WIDTH : natural := (PPU_PALETTE_COLOR_WIDTH + PPU_PALETTE_INDEX_WIDTH); -- global palette index width
 	constant PPU_TMM_ADDR_WIDTH : natural := 16; -- tilemap memory ram bus address width
 	constant PPU_TMM_DATA_WIDTH : natural := 15; -- tilemap memory ram bus data width
 	constant PPU_BAM_ADDR_WIDTH : natural := 11; -- background attribute memory ram bus address width
@@ -32,7 +38,18 @@ package ppu_consts is
 	constant PPU_BG_CANVAS_TILE_V_WIDTH : natural := 5; -- bits needed to describe vertical bg tile index (grid coordinates)
 	constant PPU_TILE_INDEX_WIDTH : natural := 10; -- bits needed to index a tile from TMM memory
 	constant PPU_PIXELS_PER_TILE_WORD : natural := 5; -- pixels defined in one word in TMM memory
-	constant PPU_SPRITE_PIXELS_PER_WORD : natural := 52; -- words needed for a single sprite
+	constant PPU_SPRITE_WORD_COUNT : natural := 52; -- words needed for a single sprite
 	constant PPU_PIXEL_BIT_WIDTH : natural := 3; -- bits needed to identify pixel in TMM word
+	constant PPU_TILE_BIT_WIDTH : natural := (PPU_SPRITE_WIDTH * PPU_SPRITE_HEIGHT * PPU_PALETTE_COLOR_WIDTH); -- bits in single tile
+	constant PPU_TMM_CACHE_FETCH_C_COUNT : natural := PPU_SPRITE_WORD_COUNT + 1;
+	constant PPU_TMM_CACHE_FETCH_A_COUNT : natural := PPU_TMM_CACHE_FETCH_C_COUNT * PPU_FG_SPRITE_COUNT; -- amount of clocks to fetch new TMM cache
+	constant PPU_TMM_CACHE_FETCH_A_WIDTH : natural := ceil_log2(PPU_TMM_CACHE_FETCH_A_COUNT);
 end package ppu_consts;
-
+package body ppu_consts is
+	-- https://stackoverflow.com/questions/21783280/number-of-bits-to-represent-an-integer-in-vhdl
+	-- Returns number of bits required to represent val in binary vector
+	function ceil_log2(n : natural) return natural is
+	begin
+		return natural(integer(ceil(log2(real(n - 1)))));
+	end function;
+end package body ppu_consts;