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Add The Castle mapper (32KB RAM) support

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Introduce mapper_castle signal and CRC detection (CRC16-CCITT 0xEF38) for The Castle (Japan) SG-1000 cartridge. Treat The Castle as a 32KB cart with 32KB RAM at 0x8000-0xFFFF by updating sc_cart_ram_32k/sc_cart_ram_low, nvram addressing, and ROM read gating (prevent ROM reads when Castle RAM is mapped into the upper half). Also exclude the Castle mapper from System E / SC-3000 mapper handling and add explanatory comments.
This commit is contained in:
Fabricio Breve
2026-04-29 11:23:49 -03:00
parent a2c0a09ceb
commit e9130e7b04
1 changed files with 12 additions and 6 deletions
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18
rtl/system.vhd
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@@ -280,6 +280,7 @@ architecture Behavioral of system is
-- Nemesis II+ (other CRCs): plain Zemina banking ($0000-$1FFF = page 0), no special startup page
signal mapper_nemesis_auto : std_logic; -- '1' for Nemesis I (CRC 0xEE05) - needs last-page boot
signal mapper_zemina_crc : std_logic; -- '1' for other Zemina CRC matches - plain Zemina
signal mapper_castle : std_logic := '0'; -- The Castle (Japan): 32KB RAM at 0x8000-0xFFFF
signal reset_n_prev : std_logic := '0'; -- for synchronous rising-edge detection of RESET_n
signal bootloader_n_prev : std_logic := '1'; -- for rising-edge detection of bootloader_n (BIOS->cart handoff)
@@ -643,8 +644,8 @@ port map(
io_sc_legacy_port <= '1' when (A(7 downto 0)=x"DE" or A(7 downto 0)=x"DF") and palettemode='1' and gg='0' and systeme='0' else '0';
io_sc_mc_port <= '1' when A(7 downto 5)="111" and sc_multicart_en='1' and gg='0' and systeme='0' else '0';
sc_cart_ram_32k <= '1' when sc3000_en='1' and sc_cart_ram="11" else '0';
sc_cart_ram_low <= '1' when sc3000_en='1' and sc_cart_ram/="00" and A(15 downto 14)="10" else '0';
sc_cart_ram_32k <= '1' when (sc3000_en='1' and sc_cart_ram="11") or mapper_castle='1' else '0';
sc_cart_ram_low <= '1' when ((sc3000_en='1' and sc_cart_ram/="00") or mapper_castle='1') and A(15 downto 14)="10" else '0';
sc_cart_ram_high <= '1' when sc_cart_ram_32k='1' and A(15 downto 14)="11" else '0';
sc_cart_ram_rd <= sc_cart_ram_low or sc_cart_ram_high;
sc_multicart_upper <= '1' when sc_multicart_en='1' and A(15)='1' else '0';
@@ -662,7 +663,7 @@ port map(
-- 11=32KB total (32KB cart overlaying the internal 2KB window).
nvram_a <= "0000" & A(10 downto 0) when sc3000_en = '1' and sc_cart_ram = "01" else
'0' & A(13 downto 0) when sc3000_en = '1' and sc_cart_ram = "10" else
A(14 downto 0) when sc3000_en = '1' and sc_cart_ram = "11" else
A(14 downto 0) when (sc3000_en = '1' and sc_cart_ram = "11") or mapper_castle = '1' else
(nvram_p and not A(14)) & A(13 downto 0);
nvram_we <= nvram_WR;
nvram_d <= D_in;
@@ -768,7 +769,8 @@ port map(
or (A(15 downto 13)="101" and nvram_cme = '1'))
or sc_cart_ram_low='1'
or sc_cart_ram_high='1') else '0';
rom_RD <= not RD_n when MREQ_n='0' and A(15 downto 14)/="11" and sc_multicart_upper='0' else '0';
rom_RD <= not RD_n when MREQ_n='0' and A(15 downto 14)/="11" and sc_multicart_upper='0'
and not (mapper_castle='1' and A(15)='1') else '0';
color <= vdp2_color when (vdp2_y1='1' and systeme='1' and vdp_enables(1)='0') else vdp_color when vdp_enables(0)='0' else x"000";
process (clk_sys)
@@ -939,8 +941,8 @@ port map(
last_read_addr <= A; -- gyurco anti-ldir patch
end if;
if systeme = '1' or sc3000_en = '1' then
-- no System E or SC-3000 mappers
if systeme = '1' or sc3000_en = '1' or mapper_castle = '1' then
-- no System E, SC-3000, or Castle (32KB RAM) mappers
elsif mapper_4pak = '1' then
-- 4-PAK All Action mapper (per MAME sega8_4pak_device):
-- $3FFE: reg0=D; bank0=D; bank2=(reg0[5:4]+reg2)
@@ -1063,6 +1065,10 @@ port map(
end if;
end process;
-- The Castle (Japan) [SG-1000]: 32KB ROM, 32KB RAM at 0x8000-0xFFFF
-- CRC16-CCITT of last 8KB block: 0xEF38
mapper_castle <= '1' when rom_crc16_run = x"EF38" else '0';
-- Nemesis I (0xEE05): Zemina banking with $0000-$1FFF = last 8KB page at startup
mapper_nemesis_auto <= '1' when rom_crc16_run = x"EE05" else '0';
-- Plain Zemina (nem_bank0=0): Nemesis II (0x9136), F-1 Spirit (0x599E),