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[NES]Cleanup in MMC1

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This commit is contained in:
Sebastien Delestaing
2016-09-23 15:57:37 +02:00
parent 0d6df45d7f
commit 65bfa3136f
1 changed files with 3 additions and 13 deletions
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16
cores/nes/src/mmu.v
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@@ -61,24 +61,14 @@ module MMC1(input clk, input ce, input reset,
reg [4:0] prg_bank;
reg delay_ctrl; // used to prevent fast-write to the control register
wire [3:0] last_prg_index = 4'b1111;
// used to prevent overflow of the chr_sel
wire [4:0] chr_4k_banks_mask = flags[10:8] == 0 ? 5'h01 : // 8Kb CHR RAM or ROM
flags[10:8] == 1 ? 5'h03 : // 16Kb
flags[10:8] == 2 ? 5'h07 : // 32Kb
flags[10:8] == 3 ? 5'h0f : // 64Kb
flags[10:8] == 4 ? 5'h1f : // 128Kb
flags[10:8] == 5 ? 5'h1f : // not supported
flags[10:8] == 6 ? 5'h1f : 5'h1f; // not supported
// Update shift register
always @(posedge clk) if (reset) begin
shift <= 1;
control <= 5'b0_11_00;
chr_bank_0 <= 0;
chr_bank_1 <= 0;
prg_bank <= last_prg_index;
prg_bank <= 4'b1111; // might not be the actual last page index but will be masked anyway
delay_ctrl <= 0;
end else if (ce) begin
if (!prg_write)
@@ -115,7 +105,7 @@ module MMC1(input clk, input ce, input reset,
3'b10_0: prgsel = 4'b0000; // Swap 16Kb at $C000 with access at $8000, so select page 0 (hardcoded)
3'b10_1: prgsel = prg_bank[3:0]; // Swap 16Kb at $C000 with $C000 access, so select page based on prg_bank (register 3)
3'b11_0: prgsel = prg_bank[3:0]; // Swap 16Kb at $8000 with $8000 access, so select page based on prg_bank (register 3)
3'b11_1: prgsel = last_prg_index; // Swap 16Kb at $8000 with $C000 access, so select last page (hardcoded)
3'b11_1: prgsel = 4'b1111; // Swap 16Kb at $8000 with $C000 access, so select last page (hardcoded)
endcase
end
wire [21:0] prg_aout_tmp = {4'b00_00, prgsel, prg_ain[13:0]};