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Internal memory map

This mapping is used internally by FPGA/μC and when accessing flashcart from USB side.

section base size access device
SDRAM 0x0000_0000 64 MiB RW SDRAM
Flash [1] 0x0400_0000 16 MiB RW/R Flash
Data buffer 0x0500_0000 8 kiB RW BlockRAM
EEPROM 0x0500_2000 2 kiB RW BlockRAM
64DD/MCU buffer 0x0500_2800 1 kiB RW BlockRAM
FlashRAM buffer [2] 0x0500_2C00 128 bytes R BlockRAM
N/A [3] 0x0500_2C80 to 0x07FF_FFFF R N/A
  • Note [1]: Flash memory region 0x04E0_0000 - 0x04FD_FFFF is write protected as it contains N64 bootloader. This section can be overwritten only via firmware update process.
  • Note [2]: Due to BlockRAM usage optimization this section is read only.
  • Note [3]: Read returns 0. Maximum accessible address space is 128 MiB.

PI memory map

This mapping is used when accessing flashcart from N64 side.

section base size access mapped base mapped device mapped bus mapped when
64DD registers 0x0500_0000 2 kiB RW N/A 64DD Controller reg bus DD mode is set to REGS or FULL
64DD IPL [1] 0x0600_0000 4 MiB R 0x03BC_0000 SDRAM mem bus DD mode is set to IPL or FULL
SRAM [2] 0x0800_0000 128 kiB RW 0x03FE_0000 SDRAM mem bus SRAM save type is selected
SRAM banked [2][3] 0x0800_0000 96 kiB RW 0x03FE_0000 SDRAM mem bus SRAM banked save type is selected
FlashRAM [2][4] 0x0800_0000 128 kiB RW 0x03FE_0000 FlashRAM Cntrl./SDRAM reg/mem bus FlashRAM save type is selected
Bootloader 0x1000_0000 1920 kiB R 0x04E0_0000 Flash mem bus Bootloader switch is enabled
ROM [5] 0x1000_0000 64 MiB RW 0x0000_0000 SDRAM mem bus Bootloader switch is disabled
ROM shadow [6] 0x13FE_0000 128 kiB R 0x04FE_0000 Flash mem bus ROM shadow is enabled
ROM extended 0x1400_0000 14 MiB R 0x0400_0000 Flash mem bus ROM extended is enabled
ROM shadow [7] 0x1FFC_0000 128 kiB R 0x04FE_0000 Flash mem bus SC64 register access is enabled
Data buffer 0x1FFE_0000 8 kiB RW 0x0500_0000 Block RAM mem bus SC64 register access is enabled
EEPROM 0x1FFE_2000 2 kiB RW 0x0500_2000 Block RAM mem bus SC64 register access is enabled
64DD/MCU buffer [8] 0x1FFE_2800 1 kiB RW 0x0500_2800 Block RAM mem bus SC64 register access is enabled
FlashRAM buffer [8] 0x1FFE_2C00 128 bytes R 0x0500_2C00 Block RAM mem bus SC64 register access is enabled
SC64 registers 0x1FFF_0000 28 bytes RW N/A Flashcart Interface reg bus SC64 register access is enabled
  • Note [1]: 64DD IPL share SDRAM memory space with ROM (last 4 MiB minus 128 kiB for saves). Write access is always disabled for this section.
  • Note [2]: SRAM and FlashRAM save types share SDRAM memory space with ROM (last 128 kiB).
  • Note [3]: 32 kiB chunks are accessed at 0x0800_0000, 0x0804_0000 and 0x0808_0000.
  • Note [4]: FlashRAM read access is multiplexed between mem and reg bus, writes are always mapped to reg bus.
  • Note [5]: Write access is available when ROM_WRITE_ENABLE config is enabled.
  • Note [6]: This address overlaps last 128 kiB of ROM space allowing SRAM and FlashRAM save types to work with games occupying almost all of ROM space (for example Pokemon Stadium 2). Reads are redirected to last 128 kiB of flash.
  • Note [7]: Always accessible regardless of ROM shadow switch.
  • Note [8]: Used internally and exposed only for debugging.

Address decoding limitations

Current implementation of PI interface checks only upper 16 bits of address. Bus and device are chosen only from value of starting address. In specific situations this could lead to unexpected behavior when performing R/W operations crossing 64 kiB boundaries. Page size (as called by N64 docs) is configurable by PI_BSD_DOMn_PGS register. Maximum page size can be set up to 128 kiB blocks. PI controller inside N64 will automatically reissue address at set boundary when performing R/W operation that crosses it.

For example, setting largest page size then doing 128 kiB read starting from address 0x1FFE_0000 will select mem bus and start fetching data from mapped internal address 0x0500_0000. SC64 registers are available at base address 0x1FFF_0000 (0x1FFE_0000 + 64 kiB), but are connected to reg bus. As a consequence of this design data read by N64 in single transaction will not contain values of SC64 registers at 64 kiB offset.

Flash mapped sections

Due to flash memory timing requirements it's not possible to directly write data from N64 side. Special commands are provided for performing flash erase and program. During those operations avoid accessing flash mapped sections. Data read will be corrupted and erase/program operations slows down.

SC64 registers

SC64 contains small register region used for communication between N64 and controller code running on the μC. Protocol is command based with support for up to 256 different commands and two 32-bit argument/result values per operation. Command execution finish can be optionally signaled with "cart interrupt"

name address size access usage
SCR 0x1FFF_0000 4 bytes RW Command execution and status
DATA0 0x1FFF_0004 4 bytes RW Command argument/result 0
DATA1 0x1FFF_0008 4 bytes RW Command argument/result 1
IDENTIFIER 0x1FFF_000C 4 bytes RW Flashcart identifier
KEY 0x1FFF_0010 4 bytes W SC64 register access lock/unlock
IRQ 0x1FFF_0014 4 bytes W IRQ clear and enable
AUX 0x1FFF_0018 4 bytes RW Auxiliary interrupt data channel

0x1FFF_0000: SCR

name bits access meaning
CMD_BUSY [31] R 1 if dispatched command is pending/executing
CMD_ERROR [30] R 1 if last executed command returned with error code
BTN_IRQ_PENDING [29] R 1 if flashcart has raised a "button pressed" interrupt
BTN_IRQ_MASK [28] R 1 means "button pressed" interrupt is enabled (always 1)
CMD_IRQ_PENDING [27] R 1 if flashcart has raised a "command finish" interrupt
CMD_IRQ_MASK [26] R 1 means "command finish" interrupt is enabled (always 1)
USB_IRQ_PENDING [25] R 1 if flashcart has raised an "USB not empty" interrupt
USB_IRQ_MASK [24] R 1 means "USB not empty" interrupt is enabled
AUX_IRQ_PENDING [23] R 1 if flashcart has raised an "AUX not empty" interrupt
AUX_IRQ_MASK [22] R 1 means "AUX not empty" interrupt is enabled
N/A [21:9] N/A Unused, write 0 for future compatibility
CMD_IRQ_REQUEST [8] RW Raise cart interrupt signal when command finishes execution
CMD_ID [7:0] RW Command ID to be executed

Note: Write to this register raises CMD_BUSY bit and clears CMD_ERROR bit. Flashcart then will start executing provided command.

0x1FFF_0004: DATA0 / 0x1FFF_0008: DATA1

name bits access meaning
DATA0/1 [31:0] RW Command argument (W) or result (R)

Note: Result is valid only when command has finished execution and CMD_BUSY bit is reset. When CMD_ERROR is set then DATA0 register contains error code.

0x1FFF_000C: IDENTIFIER

name bits access meaning
IDENTIFIER [31:0] R Flashcart identifier (ASCII SCv2)

0x1FFF_0010: KEY

name bits access meaning
KEY [31:0] W Value to be put into lock/unlock sequencer

Note: By default from cold boot (power on) or console reset (NMI) flashcart will disable access to SC64 specific memory regions. KEY register is always enabled and listening for writes regardless of lock/unlock state. To enable SC64 registers it is necessary to provide sequence of values to this register. Value 0x00000000 will reset sequencer state. Two consecutive writes of values 0x5F554E4C and 0x4F434B5F will unlock all SC64 registers if flashcart is in lock state. Value 0xFFFFFFFF will lock all SC64 registers if flashcart is in unlock state.

0x1FFF_0014: IRQ

name bits access meaning
BTN_CLEAR [31] W Write 1 to clear "button pressed" interrupt
CMD_CLEAR [30] W Write 1 to clear "command finish" interrupt
USB_CLEAR [29] W Write 1 to clear "USB not empty" interrupt
AUX_CLEAR [28] W Write 1 to clear "AUX not empty" interrupt
N/A [27:12] N/A Unused, write 0 for future compatibility
USB_IRQ_DISABLE [11] W Write 1 to disable "USB not empty" interrupt
USB_IRQ_ENABLE [10] W Write 1 to enable "USB not empty" interrupt
AUX_IRQ_DISABLE [9] W Write 1 to disable "AUX not empty" interrupt
AUX_IRQ_ENABLE [8] W Write 1 to enable "AUX not empty" interrupt
N/A [7:0] N/A Unused, write 0 for future compatibility

Note: All interrupts are cleared and disabled when any of the following events occur:

  • Hard reset
  • NMI reset
  • SC64 registers lock

SC64 interrupts are completely disabled when register access is not enabled.

0x1FFF_0018: AUX

This register can be used as a very simple interface to the PC via USB. Writing to this register generates an USB transfer with the contents of the written data. New data available in the register are signaled via cart interrupt that needs to be enabled beforehand by setting AUX_IRQ_ENABLE bit in the IRQ register. Status can be also manually polled by checking AUX_IRQ_PENDING bit in SCR register. Interrupt needs to be acknowledged by setting AUX_CLEAR bit in the IRQ register. There is no flow control, use this register as a ping-pong interface. For example, PC sends AUX data, N64 receives interrupt, reads the data then writes to this register with a response. This flow can be reversed if needed - N64 can be the initiating side.

name bits access meaning
DATA [31:0] RW Arbitrary data

This register is used by the upload process in the sc64deployer to notify running app on the N64 about certain events. All DATA values with upper 8 bits set to 1 (0xFFxxxxxx) are reserved for internal use by the SC64. Refrain from using these values in your app for uses other than listed below. Currently defined reserved DATA values are:

  • 0xFF000000 - Ping - no-op command to test if app running on the N64 is listening to the AUX events.
  • 0xFF000001 - Halt - causes the running app to stop all activity and wait in preparation for uploading new ROM to the SC64. App still should listen to the AUX interrupt and respond to other messages.
  • 0xFF000002 - Reboot - causes the running app to perform soft reboot by reloading IPL3 from the ROM and start executing it.

App running on the N64 shall respond to the AUX message with the same DATA value as incoming event for all events listed above, unless it's specified otherwise.

Command execution flow

Without interrupt

  1. Check if command is already executing by reading CMD_BUSY bit in SCR register (optional).
  2. Write command argument values to DATA0 and DATA1 registers, can be skipped if command doesn't require it.
  3. Write command ID to SCR register.
  4. Wait for CMD_BUSY bit in SCR register to go low.
  5. Check if CMD_ERROR bit in SCR is set:
    • If error is set then read DATA0 register containing error code.
    • If error is not set then read DATA0 and DATA1 registers containing command result values, can be skipped if command doesn't return any values.

With interrupt

  1. Check if command is already executing by reading CMD_BUSY bit in SCR register (optional).
  2. Write command argument values to DATA0 and DATA1 registers, can be skipped if command doesn't require it.
  3. Write command ID to SCR register and set CMD_IRQ_REQUEST bit high.
  4. Wait for cart interrupt.
  5. Check (in cart interrupt handler) if CMD_IRQ_PENDING bit in SCR register is set high.
  6. Clear interrupt by setting CMD_CLEAR bit high in the IRQ register.
  7. Check if CMD_ERROR bit in SCR is set:
    • If error is set then read DATA0 register containing error code.
    • If error is not set then read DATA0 and DATA1 registers containing command result values, can be skipped if command doesn't return any values.