IKAOPM

YM2151 Verilog core for FPGA implementation. It was reverse-engineered with only Yamaha's datasheet and the die shot from siliconpr0n. This core does not reference any existing hard/soft core. © 2023 Sehyeon Kim(Raki)

Copyrighted work. Permitted to be used as the header image. Painted by SEONGSU.

Features

• A cycle-accurate, die shot based, BSD2 licensed core.
• FPGA proven. Special thanks go to @kunichiko and @jburks.
• Accurately emulates most signals of the actual chip.
• Emulates uneven mixing behavior of the actual chip's accumulator.
• All LSI test bits are implemented.

Module instantiation

The steps below show how to instantiate the IKAOPM module in Verilog:

1. Download this repository or add it as a submodule to your project.
2. You can use the Verilog snippet below to instantiate the module.

//Verilog module instantiation example
IKAOPM #(
    .FULLY_SYNCHRONOUS          (1                          ),
    .FAST_RESET                 (0                          ),
    .USE_BRAM                   (0                          )
) u_ikaopm_0 (
    .i_EMUCLK                   (                           ),

    .i_phiM_PCEN_n              (                           ),
    //.i_phi1_PCEN_n              (                           ), //compilation option
    //.i_phi1_NCEN_n              (                           ),

    .i_IC_n                     (                           ),

    .o_phi1                     (                           ),

    //.o_EMU_BUSY_FLAG            (                           ), //compilation option
    .i_CS_n                     (                           ),
    .i_RD_n                     (                           ),
    .i_WR_n                     (                           ),
    .i_A0                       (                           ),

    .i_D                        (                           ),
    .o_D                        (                           ),
    .o_D_OE                     (                           ),

    .o_CT1                      (                           ),
    .o_CT2                      (                           ),

    .o_IRQ_n                    (                           ),

    .o_SH1                      (                           ),
    .o_SH2                      (                           ),

    .o_SO                       (                           ),

    .o_EMU_R_SAMPLE             (                           ),
    .o_EMU_R_EX                 (                           ),
    .o_EMU_R                    (                           ),

    .o_EMU_L_SAMPLE             (                           ),
    .o_EMU_L_EX                 (                           ),
    .o_EMU_L                    (                           )
);

3. Attach your signals to the port. The direction and the polarity of the signals are described in the port names. The section below explains what the signals mean.

• FULLY_SYNCHRONOUS 1 makes the entire module synchronized(default, recommended). A 2-stage synchronizer is added to all asynchronous control signal inputs. Hence, i_EMUCLK at 3.58 MHz, all write operations are delayed by 2 clocks. If 0, 10 latches are used. There are two unsafe D-latches to emulate an SR-latch for a write request, and an 8-bit D-latch to temporarily store a data bus write value. When using the latches, you must ensure that the enable signals are given the appropriate clock or global attribute. Quartus displays several warnings and treats these signals as GCLK. Because the latch enable signals are considered clocks, the timing analyzer will complain that additional constraints should be added to the bus control signals. I have verified that these asynchronous circuits work on an actual chip, but timing issues may exist.
• FAST_RESET When set to 0, assertion of the i_IC_n for at least 64 cycles of phiM should be guaranteed during the operation of i_EMUCLK and i_phiM_PCEN_n to ensure reset of all pipelines in the IKAOPM. If it is 1, then if i_IC_n is logic low, it forces phi1_cen, the internal divided clock enable, to be enabled so that the pipelines reset at the same rate as the i_EMUCLK. Therefore, i_phiM_PCEN_n does not need to operate at this time.
• USE_BRAM When set to 1, shift registers are implemented by block RAMs, reducing the usage of general logic cells (LUT + flip-flop). Default is 0 - use the general logic to implement shift registers.
• i_EMUCLK is your system clock.
• i_phiM_PCEN_n is the clock enable(negative logic) for positive edge of the phiM.
• i_IC_n is the synchronous reset. To flush every pipelines in the module, IC_n must be kept at zero for at least 64 phiM cycles. Note that while the i_IC_n is asserted, the i_phiM_PCEN_n must be operating.
• o_D_OE is the output enable for FPGA's tri-state I/O driver.
• o_SO is the YM3012-type serial lossy audio output.
• o_EMU_R_SAMPLE and o_EMU_L_SAMPLE are external latch enable strobes. You can adjust pulse width by altering the parameter SAMPLE_STROBE_LENGTH in IKAOPM_acc.v. Because the YM2151 does not update samples simultaneously, there is the corresponding strobe for each of the two channels. Therefore, if you are configuring a system that requires both channels to be updated together, you can use only one channel's strobe. This is because the other channel's value will not be changed while one is being updated.
• o_EMU_R_EX and o_EMU_L_EX are the 16-bit signed full-range audio outputs. Not recommended.
• o_EMU_R and o_EMU_L are the 16-bit signed lossy audio outputs. Recommended.

CT2 and CT1 port description

Pin number 8 and 9 of the YM2151 are used as GPO ports. They are referred to as CT2 and CT1 respectively, but unfortunately Yamaha doesn't seem to have taken the naming of them seriously. There are datasheets that have CT2 and CT1 reversed in order. Looking at the die shot, bit 7 of the 0x1B register is connected to the pin 8, and bit 6 is connected to the pin 9. I assume that in this core, bit 7 of the 0x1B register = CT2 = pin 8, bit 6 of the same register = CT1 = pin 9. In addition, the pin that the internal data lfo_clk flows out of when test mode is turned on is CT1 = pin 9.

Compilation options

• IKAOPM_DEBUG You can view the values inside like a static storage.
• IKAOPM_BUSY_FLAG_ENABLE A busy flag for an asynchronous FIFO that performs delayed write for a faster CPU bus. This signal is equal to o_D[7].
• IKAOPM_USER_DEFINED_CLOCK_ENABLES For efficiency in clocking, you can provide the clock enables used by IKAOPM from outside of the module. Read the comments in the IKAOPM.v for recommended timings.

FPGA resource usage

• Altera EP4CE6E22C8: 2231 LEs, 1330 registers, BRAM 6608 bits, fmax=73.83MHz(slow 85C)
• Altera 5CSEBA6U23I7(MiSTer): 851 ALMs, 1490 registers, BRAM 2952 bits, 1 DSP block, fmax=143.64MHz(slow 100C)
• Xilinx XC7Z020CLG400(Zynq7020): 1174 LUTs, 116 LUTRAMs, 1579 registers, BRAM 2.5 blocks(8192 bits)
• Lattice ICE40UP5K-SG48: with USE_BRAM=1: 4516 LC (85%), 10 RAM blocks.