Memory bank map
| Bank(s) | Description |
|---|---|
| 0-127 | First PSRAM (8 MB) |
| 128-255 | Second PSRAM (8 MB, optional) |
| 256-499 | Unused (open bus) |
| 500 | Bootrom mirror (pin strap/PCv2 boot location) |
| 501-509 | Unused (open bus) |
| 510 | SPI RX buffer (read only, 512 bytes mirrored) |
| 511 | Bootrom (WS/WSC boot location) |
The PSRAM banks are writable by using the self flash mode (port 0xCE), which maps ROM at the point in the address space at which RAM usually sits (0x10000-0x1FFFF).
Note that while it is technically possible to read the SPI RX buffer and bootrom in the RAM bank, the values read will be incorrect - the RAM bank only supports byte accesses, while these banks only support 16-bit wide word accesses.
| Bank(s) | Description |
|---|---|
| 0-7 | SRAM (512 KB) |
| 8-13 | Unused (open bus) |
| 14 | IPC buffer (512 bytes mirrored) |
| 15 | SPI TX buffer (write only, 512 bytes mirrored) |
This area is used for inter-process communication by software that targets the nileswan.
| Address | Size | Description |
|---|---|---|
| 0x000 | 2 | 0xAA55 if area valid |
| 0x002 | 1 | Cold boot entrypoint |
| 0x003 | 1 | TF card status |
| 0x004 | 4 | Reserved |
| 0x008 | 24 | Cold boot register backup: AX, BX, CX, DX, SP, BP, SI, DI, DS, ES, SS, FLAGS |
| 0x020 | 184 | Cold boot I/O port backup: 0x00 ~ 0xB7 |
| 0x0D8 | 8 | Reserved |
| 0x0E0 | 288 | Free to use for programs |
- 0 - FFFF:0000 (standard - WS/WSC)
- 1 - 4000:0000 (alternate #1)
- 2 - 4000:0010 (alternate #2 - PCv2)
7 bit 0
---- ----
bttt tttt
|||| ||||
|+++-++++- TF card type
| - 0x00: no card
| - 0x01: MMC (older)
| - 0x02: MMC (newer)
| - 0x04: TF (older)
| - 0x08: TF (newer)
+--------- Card uses block instead of byte addressing
When disabling removable storage card power, this byte should also be set to 0; otherwise, filesystem drivers may fail to work correctly.
The SPI RX and TX buffer are double-buffered. This means one buffer is visible to the console, while the other is used by the FPGA for facilitating an ongoing SPI transfer. These buffers can be swapped using SPI_CNT.