Next186 - DECA port

DECA Top level for NES by Somhic (1/11/21) adapted from Neptuno port by Distwave (https://github.com/neptuno-fpga/Next186_SoC).

Now compatible with Deca Retro Cape 2 (new location for 3 pins of old SDRAM modules). Otherwise see pinout below to connect everything through GPIOs.

Features:

• HDMI video output (special resolution will not work on all LCD monitors)
• VGA 444 video output is available through GPIO (see pinout below).
• Audio Line out (3.5 jack green connector) and HDMI audio output
• PWM audio is available through GPIO
• MIDI output and MIDI I2S mixing available though an external mt32-pi synthesizer (MIDI2SBC)
• Requires an special SD card with BIOS flashed into it (see notes below)

Additional hardware required:

• SDRAM Mister module.
  • Tested with 32 MB SDRAM board for MiSTer (extra slim) XS_2.2 (see connections) (sdram clk at 125 MHz -2.5ns did not work; at 100 MHz -2ns worked, but other testers reported that only worked the 80 MHz -2ns version)
  • Tested with a dual memory module v1.3 with 3 pins (see connections + 3pins) with a memtest of 140 MHz (sdram clk at 100 MHz -1.5 ns worked but after adding Alastair's change in sdram controller to allow 128 MB modules it stopped loading Manhunter 1 game; changed sdram clk to 80MHz -2ns then worked).
  • Tested with a dual memory module v1.3 with 3 pins (see connections + 3pins) with a memtest of 120 MHz (sdram clk 100 MHz -1.5ns hanged when loading games but with sdram clk of 100 MHz -2ns worked).
  • If you want to use a 128 MB Mister module, edit rtl/sdram.v, uncomment line 157 and compile the project again.
• PS/2 Keyboard connected to GPIO (see pinout below)

Versions:

• See changelog in rtl_deca/Next186_SoC.v
• current version: 0.4
  • added line 157 in sdram.v to allow 128 MB modules but left it commented
  • sdram clock at 80 MHz -2ns phase shift, for better compatibility

Compiling:

• Load project rtl_deca/Next186_SoC.qpf
• sof/svf files already included in rtl_deca/output_files/

Pinout connections:

UART not connected as diagram. See pins at Next186_SoC.qsf.

MIDI_out is connected to UART_TXD as per diagram above.

Joystick not available.

Others:

• Button KEY0 is a reset button

SD card

This core needs it's own SD card inserted with the BIOS flashed in the last 8 kB and first 64 sectors.

Freedos.img includes FreeDOS and the BIOS needed. Flash it into an SD (SDHC type, 4 GB or more).

STATUS

• Working fine

• HDMI video outputs special resolution, so does not work in all monitors.