Super NES Programming/Super FX tutorial
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When/if this tutorial is finished, it will show how to use the Super FX chip, which is included in 8 released games, most notably Star Fox, Doom, and Yoshi's Island.
[edit] Internals
As the Super FX chip is a processor itself, programming for it is done with Super FX assembly language. The Super FX chip has 4 RAM banks of 64 Kb each, or a total of 256 kilobytes of RAM.
[edit] Registers
The Super FX chip has 16 general-purpose registers labeled R0 to R15. They are each 16 bits.
| Register | Address | Description |
| R0 | 3000 | default source/destination register |
| R1 | 3002 | pixel plot X position register |
| R2 | 3004 | pixel plot Y position register |
| R3 | 3006 | |
| R4 | 3008 | lower 16 bit result of lmult |
| R5 | 300a | |
| R6 | 300c | multiplier for fmult and lmult |
| R7 | 300e | fixed point texel X position for merge |
| R8 | 3010 | fixed point texel Y position for merge |
| R9 | 3012 | |
| R10 | 3014 | |
| R11 | 3016 | return address set by link |
| R12 | 3018 | loop counter |
| R13 | 301a | loop point address |
| R14 | 301c | rom address for getb, getbh, getbl, getbs |
| R15 | 301e | program counter |
There are also plenty of other internal registers:
| Name | Address | Description | Size |
| SFR | 3030 | status flag register | 16 bits |
| 3032 | unused | ||
| PRAMR | 3033 | Backup RAM register | 8 bits |
| PBR | 3034 | program bank register | 8 bits |
| 3035 | unused | ||
| ROMBR | 3036 | rom bank register | 8 bits |
| CFGR | 3037 | control flags register | 8 bits |
| SCBR | 3038 | screen base register | 8 bits |
| CLSR | 3039 | clock speed register | 8 bits |
| SCMR | 303a | screen mode register | 8 bits |
| VCR | 303b | version code register (read only) | 8 bits |
| RAMBR | 303c | ram bank register | 8 bits |
| 303d | unused | ||
| CBR | 303e | cache base register | 16 bits |
SFR status flag register bits:
| 0 | - |
| 1 | Z Zero flag |
| 2 | CY Carry flag |
| 3 | S Sign flag |
| 4 | OV Overflow flag |
| 5 | G Go flag (set to 1 when the GSU is running) |
| 6 | R Set to 1 when reading ROM using R14 address |
| 7 | - |
| 8 | ALT1 Mode set-up flag for the next instruction |
| 9 | ALT2 Mode set-up flag for the next instruction |
| 10 | IL Immediate lower 8-bit flag |
| 11 | IH Immediate higher 8-bit flag |
| 12 | B Set to 1 when the WITH instruction is executed |
| 13 | - |
| 14 | - |
| 15 | IRQ Set to 1 when GSU caused an interrupt. Set to 0 when read by 658c16 |
