SummerCart64/docs/01_memory_map.md

• Internal memory map
• PI memory map
  • Address decoding limitations
  • Flash mapped sections
• SC64 registers
  • 0x1FFF_0000: STATUS/COMMAND
  • 0x1FFF_0004: DATA0 and 0x1FFF_0008: DATA1
  • 0x1FFF_000C: IDENTIFIER
  • 0x1FFF_0010: KEY
  • 0x1FFF_0014: IRQ
• Command execution flow
  • Without interrupt
  • With interrupt

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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 buffer	0x0500_2800	256 bytes	RW	BlockRAM
FlashRAM buffer [2]	0x0500_2900	128 bytes	R	BlockRAM
N/A [3]	0x0500_2980	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 accessibe address space is 128 MiB.

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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 buffer [8]	0x1FFE_2800	256 bytes	RW	0x0500_2800	Block RAM	mem bus	SC64 register access is enabled
FlashRAM buffer [8]	0x1FFE_2900	128 bytes	R	0x0500_2900	Block RAM	mem bus	SC64 register access is enabled
SC64 registers	0x1FFF_0000	24 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 accesed 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.

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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 diferrent commands and two 32-bit argument/result values per operation. Support for interrupts is provided but currently no command relies on it, 64DD IRQ is handled separately.

name	address	size	access	usage
STATUS/COMMAND	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	Pending IRQ clear

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0x1FFF_0000: STATUS/COMMAND

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
MCU_IRQ_PENDING	[29]	R	1 if flashcart has raised a MCU interrupt
CMD_IRQ_PENDING	[28]	R	1 if flashcart has raised a command finish interrupt
N/A	[27:9]	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.

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0x1FFF_0004: DATA0 and 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 executed and CMD_BUSY bit is reset. When CMD_ERROR is set then DATA0 register contains error code.

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0x1FFF_000C: IDENTIFIER

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

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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 necesarry to provide sequence of values to this register. Value 0x00000000 will reset sequencer state. Two consequentive 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.

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0x1FFF_0014: IRQ

name	bits	access	meaning
MCU_CLEAR	[31]	W	Write 1 to clear a MCU interrupt
CMD_CLEAR	[30]	W	Write 1 to clear a command finish interrupt
N/A	[29:0]	N/A	Unused, write 0 for future compatibility

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Command execution flow

Without interrupt

1. Check if command is already executing by reading CMD_BUSY bit in STATUS/COMMAND 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 STATUS/COMMAND register.
4. Wait for CMD_BUSY bit in STATUS/COMMAND register to go low.
5. Check if CMD_ERROR bit in STATUS/COMMAND 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 STATUS/COMMAND 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 STATUS/COMMAND 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 STATUS/COMMAND register is set high.
6. Clear interrupt by setting CMD_CLEAR bit high in the IRQ register.
7. Check if CMD_ERROR bit in STATUS/COMMAND 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.