N64cart - N64 flash cartridge

• Intro
• Concept
  • Project files
  • Features
  • Memory mapping
• PCB
  • Order notes
  • Assembly notes
• Build firmware
• Build ROM Manager
• Cartridge utility
  • Build
  • How to use
  • Remote access to the cartridge
• ROMFS Manager
• Total cartridge cost (32 MB version)
• Photos of version 2
• Bill of materials for version 3
• Photos of version 3
• Remote access from an SGI Indy

Intro

N64cart is an inexpensive N64 flash cartridge you can build at home. The hardware and firmware started as a fork of Konrad Beckmann's PicoCart64, which uses a Raspberry Pi Pico as a memory controller.

The N64 cartridge connector footprint for Eagle CAD comes from SummerCart64.

The N64 ROM boot code is derived from N64FlashcartMenu and N64 DreamOS ROM.

Concept

To keep the cartridge simple and inexpensive, I used one SPI flash chip and one RP2040. Konrad's design used multiplexed PSRAM chips and two RP2040s. Flash chips rated for more than 100,000 erase/program cycles should last for many years of home use.

The RP2040's XIP interface directly addresses up to 16 MB of flash. The early design used the Extended Address (EA) register to switch between 16 MB banks on larger chips. This was slow: each bank switch required disabling XIP, switching to SPI mode to update the register, and then re-enabling XIP. N64cart now uses QSPI with 32-bit addressing, without XIP, to avoid bank switching.

The romfs filesystem maps the sectors of stored files into a contiguous address space that the N64 accesses through the PI bus. Maximum flash capacity depends on the board version: 64 MB for version 2 with a SOIC-8 or 8 × 6 mm WSON-8 package, and 128 MB for version 3 with a SOIC-16 package.

Project files

Cartridge board version 2 (SOIC-8 / WSON-8, 8 × 6 mm; 64 MB maximum)

Schematic (PDF)

Schematic (Eagle CAD)

PCB (Eagle CAD)

Gerber files

Cartridge board version 3 (SOIC-16; 128 MB maximum)

Schematic (PDF)

Schematic (Eagle CAD)

PCB (Eagle CAD)

Gerber files

Features

• One LED controlled by the N64, with WS2812 RGB support on PCB version 3 (not available on PicoCart64-lite)
• A UART port accessible from the N64 (not available on PicoCart64-lite)
• USB passthrough to the N64
• Emulation of 4/16 Kbit EEPROM
• Emulation of 256 Kbit / 1 Mbit SRAM
• Emulation of 1 Mbit FlashRAM (29L1100)
• A USB utility for accessing files on the cartridge's flash chip

Memory mapping

Registers

Register	Address	Mode
UART_CTRL	0x1fd01000	R-
UART_RXTX	0x1fd01004	RW
LED_CTRL	0x1fd01008	-W
SYS_CTRL	0x1fd0100c	RW
SSI_SR	0x1fd01010	RW
SSI_DR0	0x1fd01014	RW
FW_SIZE	0x1fd01018	R-

UART_CTRL bits

Function	Bit mask	Mode
UART_RX_AVAIL	0x01	R-
UART_TX_FREE	0x02	R-

UART_RXTX bits

Function	Bit mask	Mode
DATA	0xFF	RW

LED control bits

Function	Bit mask	Mode	Note
LED_ONOFF	0x01	-W	PCB v2 or PCB v3 without WS2812
LED_RGB	0x00ffffff	-W	PCB v3 only

SYS_CTRL bits

Function	Bit mask	Mode
EEPROM_16KBIT	0x1000	RW
FRAM_MODE	0x200	RW
SRAM_UNLOCK	0x100	RW
FLASH_MODE_QUAD	0x10	RW
FLASH_CS_HIGH	0x01	RW

SSI_SR bits

Function	Bit mask	Mode
SSI_SR_TFNF_BITS	0x01	R-
SSI_SR_RFNE_BITS	0x02	R-

SSI_DR0 bits

Function	Bit mask	Mode
DATA	0xff	RW

PCB

Order notes

Use a PCB thickness of 1.2 mm.

A stencil makes it easier to apply solder paste, but adds to the order cost.

Assembly notes

After soldering the processor and flash chip, thoroughly remove flux residue from the board. Residue can cause unstable memory operation or prevent the cartridge from working.

PCB version 2

Populate either D2 or Q1, but not both.

Leave R1 and R6 unpopulated.

PCB version 3

If LED3 is populated, leave R1 and D2 unpopulated.

Build firmware

Install the Pico SDK before building the firmware.

The default configuration is BOARD=v3 and REGION=ntsc. Pass one of these options to CMake to select a different board:

• -DBOARD=v2: cartridge version 2 with 32/64 MB flash.
• -DBOARD=pico: a generic Pico cartridge with up to 16 MB of flash, without the SI_DAT, SI_CLK, NMI, and INT signals.
• -DBOARD=pico-lite: a PicoCart64-lite cartridge with up to 16 MB of flash, with the SI_DAT, SI_CLK, NMI, and INT signals.

Select the firmware region according to the console:

Console	CMake option	ROM Manager video mode
NTSC	-DREGION=ntsc (default)	NTSC
PAL	-DREGION=pal	PAL
PAL-M / MPAL (Brazil)	-DREGION=ntsc (default)	MPAL

REGION selects the cartridge's CIC security protocol. PAL-M consoles use the same protocol as NTSC consoles, so choose the NTSC firmware build for PAL-M too. ROM Manager gets the console's TV type from libdragon and selects the video mode automatically. No separate PAL-M build is needed, though it still needs testing on a real PAL-M console.

From the repository root, build the default configuration:

cd fw
mkdir -p build
cd build
cmake ..
make -j

For example, use cmake .. -DBOARD=v2 -DREGION=pal to build for a version 2 cartridge and a PAL console.

Hold the cartridge's bootloader button while connecting it via USB, then copy fw/build/n64cart.uf2 to the RPI-RP2 drive.

Build ROM Manager

Install an N64 toolchain with libdragon built from the opengl branch.

Pass BOARD=pico to make for a generic Pico cartridge, or BOARD=pico-lite for a PicoCart64-lite cartridge. Both configurations support flash chips of up to 16 MB. No REGION option is needed: video mode selection is automatic for NTSC, PAL, and PAL-M consoles.

From the repository root:

cd rom
make

Cartridge utility

The utility formats cartridge memory and reads and writes files. Use it to upload ROMs or change the background image.

Build

For Linux and macOS, install the libusb development files. From the repository root:

cd utils
make

To build for Windows, install the MinGW toolchain. From the repository root:

cd utils
make SYSTEM=Windows

How to use

Run the following commands from the utils directory. Before using a new cartridge, format it and upload ROM Manager:

./usb-romfs format
./usb-romfs push ../rom/n64cart-manager.z64

Upload a ROM, for example:

./usb-romfs push game.z64

To change the background image:

./usb-romfs push picture.jpg background.jpg

Available commands (angle brackets indicate placeholders; square brackets indicate optional arguments):

./usb-romfs help
./usb-romfs bootloader
./usb-romfs reboot
./usb-romfs format
./usb-romfs list [-h] [path]
./usb-romfs delete <remote path>
./usb-romfs mkdir <remote path>
./usb-romfs rmdir <remote path>
./usb-romfs rename <source> <destination> [--create-dirs]
./usb-romfs push [--fix-rom] [--fix-pi-bus-speed[=12..FF]] <local filename> [<remote path>]
./usb-romfs pull <remote path> [<local filename>]
./usb-romfs free

Remote access to the cartridge

If your computer cannot connect to the cartridge directly, you can access it through a USB-connected proxy computer. This is useful for older systems without USB, such as an SGI Indy. Build the remote-access utilities from the utils directory:

make remote

If the client and proxy use different architectures or operating systems, cross-compile remote-romfs for the client by specifying the compiler:

make CC="mips-sgi-irix6o32-gcc" remote-romfs

Copy remote-romfs to the client. On the proxy computer, connect the cartridge via USB and start the proxy:

./proxy-romfs

On the client, remote-romfs takes the same commands as usb-romfs. Add the proxy's IP address before the command:

./remote-romfs <proxy IP address> <command ...>

Photos of remote access from an SGI Indy

ROMFS Manager

ROMFS Manager is a desktop application built with Qt. You can use it to browse, upload, and download files on N64cart over USB or through a remote proxy.

Total cartridge cost (32 MB version)

The following is an example cost breakdown for the 32 MB version. Shipping can cost more than the components when ordering only one or two of each item. Larger orders may qualify for free shipping.

Seller	Delivery cost	Components
Chicago Electronic Distributors	$6-$11	RP2040
Arrow	Free for orders > $50	SPI flash, resistors, capacitors, etc.
JLCPCB	$22.40	PCB

In this example, five PCBs cost $2 for the first PCB design in an order, or $4 for each additional design.

The most expensive components:

Component	Quantity	Price
RP2040	1	$1
W25Q256JVEIQ	1	$4.24
ABLS-12.000MHZ-B4-T	1	$0.26
UJ2-MIBH-G-SMT-TR	1	$0.45
LDI1117-3.3U	1	$0.34
BAT60AE6327HTSA1	2	$0.93

The remaining components (LEDs, resistors, and capacitors) came from existing stock and cost less than $1 in total.

The estimated total cost of the PCB and components is approximately $9, excluding shipping.

Photos of version 2

Bill of materials for version 3

Part	Value	Device	Package
C1	100n	C-EUC0402	C0402
C2	100n	C-EUC0402	C0402
C3	100n	C-EUC0402	C0402
C4	100n	C-EUC0603	C0603
C5	100n	C-EUC0402	C0402
C6	100n	C-EUC0402	C0402
C7	100n	C-EUC0603	C0603
C8	100n	C-EUC0402	C0402
C9	100n	C-EUC0402	C0402
C10	1uF	C-EUC0402	C0402
C11	100n	C-EUC0402	C0402
C12	100n	C-EUC0402	C0402
C13	1uF	C-EUC0402	C0402
C14	100n	C-EUC0402	C0402
C15	27pF	C-EUC0402	C0402
C16	27pF	C-EUC0402	C0402
C22	10u	C-EUC0805	C0805
D1	SL02-GS08	SL02-GS08	SOD-123
D2	GREEN	LED0603	0603
D3	RED	LED0603	0603
IC1	RP2040-QFN56	RP2040-QFN56	QFN-56
LED3	XL-5050RGBC-WS2812B	XL-5050RGBC-WS2812B	XL5050RGBCWS2812B
Q1	BSS84	BSS84	SOT23
R1	1K	R-EU_R0603	R0603
R2	1K	R-EU_R0402	R0402
R3	1K	R-EU_R0402	R0402
R4	27	R-EU_R0402	R0402
R5	27	R-EU_R0402	R0402
R12	1K	R-EU_R0603	R0603
S1		10-XX	B3F-10XX
U$1	LDI1117-3.3U	LDI1117-3.3U	LDI1117-3.3U
U2		USB	USB-MICRO-SMD
U4	MX66L1G45GMI-08G	MX66L1G45GMI-08G	SOP_16
XTAL1	ABLS-12.000MHZ-B4-T	ABLS-12.000MHZ-B4-T	XTAL_ABLS_ABR

Photos of version 3

Remote access from an SGI Indy