gbaHD

An open-source GBA consolizer.

To create a stable video signal without buffering whole frames, but rather go line-by-line, the quartz crystal of the GBA is removed. Instead, the FPGA generates the clock signal for the GBA.

Note

The latest bitstream (v1.4A) only works in conjunction with a Mancloud shield. I will update the Arduino FW in the upcoming days, so the latest bitstream can be used with all gbaHD.

Wiring

You need some basic soldering skills to wire all signals of the GBA to the FPGA board and the controller to the Arduino. All responsibility is on you. I do not take any responsibility for any potential damages. The following wiring works well for me. Yet again, all risk is up to you. If you want a more out-of-the-box experience, I strongly suggest you to do not tinker around with your devices. This is a simply hobby project of mine without a lot of testing.

In general, the test points of the GBA motherboard are not made for a lot of soldering, so try to keep your soldering quick.

SEA pins

The following figure shows an overview of the pins used for signals on the Spartan Edge Accelerator board and the pin names used.

Video signals

The following figure shows the test points for the display signals on the GBA motherboard. I only used a 32 pin model so far, but the 40 pin should have a similar layout. The test points can be found on the frontside of the GBA motherboard close to the top.

The connections between the GBA display signals and the FPGA board are as follows (check the previous figures for the pin names). The "GBA Testpoint" column notes the testpoint to be connected to the corresponding FPGA pin. The next columns (GBA LCD XX-pin) give additional information where this signal is placed on the display ribbon cable.

FPGA Pin	GBA Testpoint	GBA LCD 40-pin	GBA LCD 32-Pin	GBA SP 34-Pin
IO0	2	26	25	25
IO1	5	23	22	22
ARD5	6	22	21	21
IO2	7	21	20	20
ARD6	8	20	19	19
IO3	9	19	18	18
ARD7	10	17	16	16
IO4	11	16	15	15
ARD8	12	15	14	14
IO5	13	14	13	13
ARD9	14	13	12	12
IO6	15	12	11	11
ARD10	16	11	10	10
IO7	17	10	9	9
ARD11	18	9	8	8
ARD13	19	8	7	7
IO9	22	3	2	2

Audio signals

The GBA generates a stereo 8 bit audio signals as a PWM which is then amplified. We pick up both PWM signals using the following two connections (the test point names can be found on the silkscreen of the GBA motherboard).

GBA Test Point	FPGA Pin
S01	ARD2
S02	ARD3

Clock signal

The clock crystal has to be removed and a pad of the former crystal is connected to an FPGA pin. The following figure shows which pad has to be connected (the highlighted one) to the FPGA pin.

GBA	FPGA Pin
XTAL pad	IO8

Controller signals

A cheap Arduino (e.g., a small Nano) handles the controller input (the FPGA board is not used here, as we would run out of pins here). The following figure shows the pinout of a SNES controller plug.

The SNES controller port is connected to the Arduino pins as follows:

SNES controller	Arduino Pin
5V	5V
Clk	A1
Latch	A0
Data	A2
Gnd	Gnd

The following table shows the connections between the GBA motherboard and Arduino pins for simulating the button presses.

GBA Test Point	Arduino Pin
TP6	D2
TP7	D3
TP5	D4
TP4	D5
TP0	D6
TP1	D7
TP9	D8
TP8	D9
TP3	D10
TP2	D11

Arduino-FPGA connection

To activate or change the pixel grid, a connection between the Arduino and the FPGA board is needed.

FPGA Pin	Arduino Pin
ARD4	A3

Power connections

The GBA and Arduino can be powered via pins of the FPGA board. For the GBA, the battery holders on the motherboard can be desoldered, as they are not required anymore. Then connect the "B+" pad of the GBA motherboard to the "3V3" pin of the SEA board and the GBA's "B-" pad to a GND pin of the SEA board. Keep the power switch of the GBA on the ON position (preferably fix it in this position, as the switch is quite smooth-running).

The Arduino requires 5V instead of 3.3V. For this, put the jumper "PWR_MODE" to the "ON" position. Then connect the 5V pin of the SEA board's Arduino ICSP pins to the 5V pin of the Arduino.

Custom Borders

Custom borders are currently in a kind of experimental state. Border images have to be in the dimensions of 320x180 pixels (going with the same resolution of the Game Boy). Only the border is taken into account, the display area (middle 240x160) is ignored (see template.bmp). To generate a custom border, execute

makeBorder.py <IMAGEFILE> (<CUTBITS>)

The first parameter is the image file for the border, the second is an optional parameter for reducing the image color depth. After executing the script a new .vhdl should have been created. Replace the original borderGen.vhdl with this one and run the synthesis.

If the synthesis fails, the border is too complex. Try to simplify the border image or use the color depth reduction of the makeBorder.py script. The optional parameter sets the number of bits to reduce in color space. E.g., setting CUTBITS to 2 will reduce the color depth per color from 8 bits to 6 bits.

OSD, Smoothing and Pixel Grid

A 2x smoothing and 4x smoothing can be activated. These are slightly adapted versions of the Scale2x algorithm. Note: Smoothing is currently disabled for 1080p resolution.

The pixel grid feature is currently also in an experimental state. Two different pixel grids can be applied, a "bright" pixel grid (AGS feeling) or a "dark" pixel grid (AGB feeling).

To enter the OSD, press L+R+Select+Right. Smoothing and pixel grids can be activated there.

For the OSD, the connection between the FPGA board and the Arduino board (see previous sections) needs to be wired.

FPGA Firmware

You can find the latest bitstream under the folder bitstream.

TODOs

README TODO:

• Describe the overall project.
• Describe the different modules.
• Describe pinouts.
• Describe GBA video timing.