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Quickdev2 Progress

After building the [quickdev16](http://www.assembla.com/spaces/quickdev16/wiki) in the summer of 2010 we decided to work on
a 2nd version off the quickdev16, which we called quickdev2. All this work was done in the summer of 2010 but i never got around
to finish the project nor to blog about it. So here is a little overview:

The next quickdev should be a little bit faster and should have more features.
So we selected a new CPU, the Atmel [at90usb1287](http://www.atmel.com/dyn/products/product_card.asp?part_id=3875) that can handle USB via hardware and has more SRAM. To simplify the logic part we opted for a XILINX CPLD [xc95144xl](http://www.xilinx.com/support/documentation/data_sheets/ds056.pdf).
We used a bigger Cypress 16-Mbit SRAM [CY62167E](http://www.cypress.com/?rID=37630).
The AVR would expose the USB interface to the PC side, as a masstorage device using the [LUFA](http://www.fourwalledcubicle.com/LUFA.php) library. The
AVR has a data bus to the CPLD. The CPLD is also connected to the external SRAM.
In the CPLD we implemented a SREG, counter, commandmuxer and memory interface in [Verilog](http://en.wikipedia.org/wiki/Verilog).

The system top looks like this:

module system (

    inout [7:0] sram_data,
    output [20:0] sram_addr,
    output sram_oe_n,
    output sram_we_n,
    output sram_ce_n,


    output [7:0] snes_data,
    input [20:0] snes_addr,

    inout [7:0] avr_data,
    input [7:0] avr_ctrl,
    input avr_clk,
    output [7:0] debug
);

We have a 8 bit data bus and 21 bit address bus to the SRAM. 3 extra lines for OE,WE and CE.
Then there is the same setup for the SNES side. 8 Data and 21 address line. No more control lines to
the SNES are currently implemented. There is a 8 bit data and 8 bit control bus to the AVR.
Finally we have a CLK line from the AVR to the CPLD and a 8bit debug bus.
The AVR clocks its own clock into the CPLD, which is feed into a DCM and is divided by 2.
This clock signal is feed into the FSM and SREG internally.
The avr_ctrl bus is feed into a commandmuxer which
drives the other components on the CPLD. Foremost it drives a FSM which manages the
data routing between AVR <-> SRAM and SRAM <-> SNES.

module bus_fsm #(
    parameter DWIDTH = 8
)(
    input                   clk,
    input                   reset,
    input                   we_n,
    input                   oe_n,
    inout   [DWIDTH-1:0]    avr,
    inout   [DWIDTH-1:0]    sram,
    inout   [7:0]           debug
);

parameter SIZE   =  3;
parameter IDLE    = 3'b000;
parameter WE      = 3'b001;
parameter BUFAVR  = 3'b010;
parameter BUFSRAM = 3'b011;
parameter OE      = 3'b100;


reg   [SIZE-1:0]          state;
reg   [SIZE-1:0]          next_state;
reg   [DWIDTH-1:0]        buffer_avr;
reg   [DWIDTH-1:0]        buffer_sram;
reg   [DWIDTH-1:0]        buffer;

assign avr = buffer_avr;
assign sram = buffer_sram;

always @ (state or we_n or oe_n)
begin : FSM_COMBO
    next_state = 3'b000;
    case(state)
    IDLE : if (we_n == 1'b0) begin
            next_state = BUFAVR;
        end else if (oe_n == 1'b0) begin
            next_state= BUFSRAM;
        end else begin
            next_state = IDLE;
        end
    BUFAVR: if (we_n == 1'b0) begin
            next_state = WE;
        end else begin
            next_state = IDLE;
        end
    BUFSRAM: if (oe_n == 1'b0) begin
            next_state = OE;
        end else begin
            next_state = IDLE;
        end
    OE : if (oe_n == 1'b0) begin
            next_state = BUFSRAM;
        end else begin
            next_state = IDLE;
        end
    WE : if (we_n == 1'b0) begin
            next_state = BUFAVR;
        end else begin
            next_state = IDLE;
        end
  endcase
end

//----------Seq Logic-----------------------------
always @ (posedge clk)
begin : FSM_SEQ
    if (reset == 1'b1) begin
        state <= #1 IDLE;
    end else begin
        state <= #1 next_state;
  end
end

//----------Output Logic-----------------------------
always @ (state)
begin : OUTPUT_LOGIC
  case(state)
    IDLE: begin
        buffer_avr <= 8'bz;
        buffer_sram <= 8'bz;
        buffer <= 8'bz;
    end
    WE: begin
        buffer_sram <= buffer;
    end
    OE: begin
        buffer_avr <= buffer;
    end
    BUFSRAM : begin
        buffer <= sram;
    end
    BUFAVR : begin
        buffer <= avr;
    end
    default : begin
        buffer_avr <= 8'bz;
        buffer_sram <= 8'bz;
    end
  endcase
end

assign debug = { clk,we_n,oe_n,state,2'bz};
endmodule

From the AVR software side a SRAM write looks like this.


void sreg_set(uint32_t addr)
{
    
    
    uint8_t i = 21;
    #if SREG_DEBUG 
    uart_putstring("sreg_set\n\r");
    #endif
    SET_AVR_SREG_EN_HI();
    while(i--) {
        if ((addr & ( 1L << i))){
            SET_AVR_SI_HI();
    #if SREG_DEBUG 
            uart_putchar('1');
    #endif
        } else {
            SET_AVR_SI_LO();
    #if SREG_DEBUG 
            uart_putchar('0');
    #endif
        }
        SET_AVR_SREG_EN_LO();
        SET_AVR_SREG_EN_HI();
    }
    #if SREG_DEBUG 
    uart_putstring("\n\r");
    #endif
}

void SRAM_write(uint32_t addr, uint8_t data)
{
    
    // set direction of data port
    AVR_DATA_DIR = 0xff;
    // load address
    sreg_set(addr);
    // disable OE and WE
    SET_AVR_OE_HI();
    SET_AVR_WE_HI();
    // wait for FSM to go into IDLE state
    nop();
    nop();
    // write data
    AVR_DATA = data;
    // enable WE
    SET_AVR_WE_LO();
    // wait for FSM to go into WE state
    nop();
    nop();
    nop();
    nop();
    // disable WE
    SET_AVR_WE_HI();
}

The development was done on our new prototype board, which Max layouted for us.
I used an [AVR Dragon](http://www.atmel.com/dyn/products/tools_card.asp?tool_id=3891) for the AVR programming part and debugging via [JTAG](http://en.wikipedia.org/wiki/Joint_Test_Action_Group). For the CPLD side i used a homebrew Xilinx [Platform cable](http://www.mikrocontroller.net/topic/168006) alongside with [ISE](http://www.xilinx.com/support/download/index.htm). I quickly stopped using the IDE and just cooked my own Makefile using the Xilinx commandline tools.

Most of the logic was developed using a testbench and running through [iverilog](http://iverilog.icarus.com/).
But having a module working in a testbench doesn't mean that it works on real hardware.
We had todo a lot of debugging on the real hardware. This involved a lot
of test probe soldering. Luckily we had my 8bit [Saleae](http://www.saleae.com/home/) LA which helped a lot to
track done some Problems. But the biggest issue was to get the timing right with the FSM for the memory bus.

We hacked this in a 3 day weekend sprint and implemented the SRAM read and write from the AVR side.
But then we hit a wall and didn't implement the SNES side. The project lost some traction.
Max had moved to Berlin we couldn't work together on the project anymore. We lost a little interest because the
[sd2snes](http://sd2snes.de/blog/) project achieved what we we intended to do and Ikari_01 did far better job then we did.
I recently got word the sd2snes is considered stable and a first batch is sold.

We plan to start working on this again. To implement the SNES side of the memory we would need to increase the speed
of the FSM to get it into IDLE state and then in SNES state within 120ns or 200ns after the SNES does a CS on the cartridge.
Since the AVR drives the CPLD clock with 20MHz, we would need some kind of PPL to run the FSM with like 60MHz, which should
be plenty to run the FSM for the SNES SRAM read.

We appreciate any comment or suggestion for the hardware design of this project.

1 Comment

Super Nintendo Talk

A while ago i held a talk at the ccc in cologne about my favorite game console the Super Nintendo. This talk covers the Super Nintendo technology in detail. Starting with the CPU and PPU, covering the cartridge memory maps and showing most of the custom chips which where used on cartridges. I also show development hardware, copier stations and the current available flashcarts. The topic emulation is also covered . The second part of the talk is about the quickdev16 project, which i did with my friend max in 2009. We built a flashcart for the SNES which is useful for developing homebrew software. The talk sums up all the details i learned during the research i made to built this kind of cartridge. I uploaded the slides, maybe someone find this useful to dive into the SNES world.

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Memory Visualizer for BSNES

Some time ago i saw this Memory Visualizer for Frodo and Vice C64 Emulator . I got inspired to do something simular for the SNES. I took this idea an hacked it right into BSNES. Right now i have 2 fields representing the WRAM and the VRAM of the SNES. So it displays different colors for read and write access to the memory areas. Due fading this generates some color blending effects. This is just a quick hack which was lying on my hd for some months. So its based BSNES version 0.59 , which is know a little outdated. It would need some more polishing and a better solution to display the 2 Ram areas. The GL cubes look a little lame. Also the emulator performance is not quite there so that the roms a little bit slow.

Download Video

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New Quickdev16 Loader

We got a new loader for the Quickdev16 firmware. The loader will replace
the current dummy loader and has a few new advantages:

qd16boot02

* Faster upload because of IRQ driven communication between SNES and AVR
* Progressbar while uploading
* Display Rom infos
* ASCII and Katakana font support
* Eyecandy: new logo design with sine wave effect and bassdrum synced
background effects..

Due to these features the loader blew up to more than 55kb, too much for
our limited space in the AVR progmem (64kb – 4kb bootloader). Our main
firmware is between 8kb and 24kb, depends on the debug-features that you
compile in. So the recent task is to either reduce the loader size by
skipping eyecandy, finding a better compression routine to compress it
in the progmem or build a minimal firmware and put parts of the loader
into the surplus 4kb eeprom on the AVR. Probably we will have to combine
the different approaches.

One reason why the firmware is that big these days is the new “minimal
debug terminal”, a serial command line where you can maintain the
Quickdev system status. You can dump memory regions from sram, switch
between the busses, write to the shared memory section, show the status
of the hardware ports and use several other usefull commands. Check the
project page for more details on the commands.

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Quickdevs are shipping

Last week we shipped the first batch of Quickdevs. The Software is feature ready, but we wanted to do some eye candy on the SNES software side, which didn’t work out yet. So software updates are coming within the next weeks.

Feel free to order at david @ optixx.org.

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