SA-1

From SnesLab
Jump to: navigation, search

Nintendo SA-1 is an enhancement chip made by Nintendo, used in 33 SNES games. The RF5A123 chip is based on the 65c816 processor, the same one used by the main SNES CPU, the RF5A22. With identical architectures to the SNES one, the chip is ideal for games and ROM hacks that would like to use the code from the main CPU, thus not having to learn an additional assembling language.

Contents

Features

With the 10.74 MHz base clock speed, which is four times faster compared to the 2.68 MHz base speed from the S-CPU. In addition to that, it includes with additional hardware circuits for data I/O, bitmap manipulation modes and additional arithmetic registers.

  • 16-bit 65c816 processor clocked at 10.74 MHz.
  • 2 kB fast internal work memory (I-RAM), clocked at 10.74 MHz.
  • Multi-processor processing, with parallel operating mode and memory sharing control.
  • Large capacity memory, with a total capability of 8 MB of ROM and 256 kB of BW-RAM, both clocked at 5.37 MHz, with ROM having an effective 10.74 MHz speed due of its 16-bit data bus.
  • High speed arithmetic hardware of multiplication, division and cumulative sum (multiply with add).
  • Bitmap and Character Conversion functions for fast graphics manipulation.
  • Custom DMA circuit for fast transfers between ROM, I-RAM and BW-RAM.
  • Variable-Length Bit data processing for enhanced algorithms such as graphics and data compression.
  • Super MMC memory mapping capabilities for BW-RAM and bank switching for multiple ROM image access and mirroring.

ROM Hacking

SA-1 Root and SA-1 Pack are known patches used for enabling SA-1 on SNES games that didn't include the chip previously and had problems with slowdown, such as Super Mario World and Gradius III.

Technical Information

There is not much technical information available on how the SA-1 chip works. Most of the findings are recent and are based on both official documents from Nintendo and experiments on real SA-1 carts. This section is getting continuously updated with new information and findings though the time. The information available here is expected to be accurate. Information about undefined behavior or design details is considered scarce right now.

Hardware Registers

The SA-1 internal registers are assigned on range $2200-$23FF, on banks $00-$3F and $80-$BF. $2200 though $22FF are write-only registers while $2300 though $23FF are read-only registers.

Register Summary

Write Registers

Address Length Code Access Description
$2200 1 byte CCNT SNES SA-1 CPU CONTROL
$2201 1 byte SIE SNES SUPER NES CPU INT ENABLE
$2202 1 byte SIC SNES SUPER NES CPU INT CLEAR
$2203 2 bytes CRV SNES SA-1 CPU RESET VECTOR
$2205 2 bytes CNV SNES SA-1 CPU NMI VECTOR
$2207 2 bytes CIV SNES SA-1 CPU IRQ VECTOR
$2209 1 byte SCNT SA-1 SUPER NES CPU CONTROL
$220A 1 byte CIE SA-1 SA-1 CPU INT ENABLE
$220B 1 byte CIC SA-1 SA-1 CPU INT CLEAR
$220C 2 bytes SNV SA-1 SUPER NES CPU NMI VECTOR
$220E 2 bytes SIV SA-1 SUPER NES CPU IRQ VECTOR
$2210 1 byte TMC SA-1 H/V TIMER CONTROL
$2211 1 byte CTR SA-1 SA-1 CPU TIMER RESTART
$2212 2 bytes HCNT SA-1 SET H-COUNT
$2214 2 bytes VCNT SA-1 SET V-COUNT
$2220 1 byte CXB SNES SET SUPER MMC BANK C
$2221 1 byte DXB SNES SET SUPER MMC BANK D
$2222 1 byte EXB SNES SET SUPER MMC BANK E
$2223 1 byte FXB SNES SET SUPER MMC BANK F
$2224 1 byte BMAPS SNES SUPER NES CPU BW-RAM ADDRESS MAPPING
$2225 1 byte BMAP SA-1 SA-1 CPU BW-RAM ADDRESS MAPPING
$2226 1 byte SBWE SNES SUPER NES CPU BW-RAM WRITE ENABLE
$2227 1 byte CBWE SA-1 SA-1 CPU BW-RAM WRITE ENABLE
$2228 1 byte BPWA SNES BW-RAM WRITE-PROTECTED AREA
$2229 1 byte SIWP SNES SA-1 I-RAM WRITE PROTECTION
$222A 1 byte CIWP SA-1 SA-1 I-RAM WRITE PROTECTION
$2230 1 byte DCNT SA-1 DMA CONTROL
$2231 1 byte CDMA Both CHARACTER CONVERSION OMA PARAMETERS
$2232 3 bytes SDA Both DMA SOURCE DEVICE START ADDRESS
$2235 3 bytes DDA Both DMA DESTINATION START ADDRESS
$2238 2 bytes DTC SA-1 DMA TERMINAL COUNTER
$223F 1 byte BBF SA-1 BW-RAM BIT MAP FORMAT
$2240 16 bytes BRF SA-1 BIT MAP REGISTER FILE
$2250 1 byte MCNT SA-1 ARITHMETIC CONTROL
$2251 2 bytes MA SA-1 ARITHMETIC PARAMETERS: MULTIPLICAND/DIVIDEND
$2253 2 bytes MB SA-1 ARITHMETIC PARAMETERS: MULTIPLIER/DIVISOR
$2258 1 byte VBD SA-1 VARIABLE-LENGTH BIT PROCESSING
$2259 3 bytes VDA SA-1 VARIABLE-LENGTH BIT GAME PAK ROM START ADDRESS

Read Registers

Address Length Code Access Description
$2300 1 bytes SFR SNES SUPER NES CPU FLAG READ
$2301 1 bytes CFR SA-1 SA-1 CPU FLAG READ
$2302 2 bytes HCR SA-1 H-COUNT READ
$2304 2 bytes VCR SA-1 V-COUNT READ
$2306 5 bytes MR SA-1 ARITHMETIC RESULT [PRODUCT/QUOTIENT/ACCUMULATIVE SUM]
$230B 1 bytes OF SA-1 ARITHMETIC OVERFLOW FLAG
$230C 2 bytes VDP SA-1 VARIABLE-LENGTH DATA READ PORT
$230E 1 byte VC SNES VERSION CODE REGISTER (OPEN BUS)

Register Details

$2200 - SA-1 CPU CONTROL

$2201 - SUPER NES CPU INT ENABLE

$2202 - SUPER NES CPU INT CLEAR

$2203 - SA-1 CPU RESET VECTOR

$2205 - SA-1 CPU NMI VECTOR

$2207 - SA-1 CPU IRQ VECTOR

$2209 - SUPER NES CPU CONTROL

$220A - SA-1 CPU INT ENABLE

$220B - SA-1 CPU INT CLEAR

$220C - SUPER NES CPU NMI VECTOR

$220E - SUPER NES CPU IRQ VECTOR

$2210 - H/V TIMER CONTROL

$2211 - SA-1 CPU TIMER RESTART

$2212 - SET H-COUNT

$2214 - SET V-COUNT

$2220-$2223 - SET SUPER MMC BANK C/D/E/F

D7 D6 D5 D4 D3 D2 D1 D0 Register
CBM 0 0 0 0 CB2 CB1 CB0 $2220
DBM 0 0 0 0 CB2 CB1 CB0 $2221
EBM 0 0 0 0 CB2 CB1 CB0 $2222
FBM 0 0 0 0 CB2 CB1 CB0 $2223

CB2~CB0: Which megabyte of the ROM to map to $C0-$CF / $D0-$DF / $E0-$EF / $F0-$FF.

CBM/DBM/EBM/FBM: Appply image projection to LoROM banks as well

Flag Bank Range
CBM Apply to banks $00-$1F
DBM Apply to banks $20-$3F
EBM Apply to banks $80-$9F
FBM Apply to banks $A0-$BF

These registers are responsible for setting up the ROM bank mapping. By default, values $00, $01, $02, $03 are loaded on power up.

Flags CBM/DBM/EBM/FBM determine if the mapping should apply to the LoROM banks as well, otherwise they will have the constant value of $00/$01/$02/$03 regardless of the ROM size. With that, it's possible to map up to 8MB at once by storing values $04,$05,$06,$07 to the registers. Snes9x 1.53 and older always treated these flags as set, making the mapping always apply to the LoROM banks.

Common values
Register $2220 $2221 $2222 $2223 Comment
Value $00 $01 $02 $03 Default value
Value $04 $05 $06 $07 Maps the first 4MB to $00-$3F; $80-$BF (LoROM) and the last 4MB to $C0-$FF.
Value $80 $81 $80 $81 Simulates the standard LoROM map with FastROM compatibility by mapping the first 2MB to $00-$3F and $80-$BF.

The Super MMC register affects all memory maps, including SNES, SA-1, SA-1 DMA and SA-1 Varible Length Bit maps. bsnes 0.7x does not apply the custom memory mapping to Variable Length Bit circuit.

Hardware verification has shown that the unused bits does absolutely nothing and therefore the maximum ROM size for SA-1 without using custom ROM controller outside the chip is 8 MB (megabytes).

$2224 - SUPER NES CPU BW-RAM ADDRESS MAPPING

$2225 - SA-1 CPU BW-RAM ADDRESS MAPPING

$2226 - SUPER NES CPU BW-RAM WRITE ENABLE

$2227 - SA-1 CPU BW-RAM WRITE ENABLE

$2228 - BW-RAM WRITE-PROTECTED AREA

$2229 - SA-1 I-RAM WRITE PROTECTION

$222A - SA-1 I-RAM WRITE PROTECTION

$2230 - DMA CONTROL

$2231 - CHARACTER CONVERSION OMA PARAMETERS

$2232 - DMA SOURCE DEVICE START ADDRESS

$2235 - DMA DESTINATION START ADDRESS

$2238 - DMA TERMINAL COUNTER

$223F - BW-RAM BIT MAP FORMAT

$2240 - BIT MAP REGISTER FILE

$2250 - ARITHMETIC CONTROL

$2251 - ARITHMETIC PARAMETERS: MULTIPLICAND/DIVIDEND

$2253 - ARITHMETIC PARAMETERS: MULTIPLIER/DIVISOR

$2258 - VARIABLE-LENGTH BIT PROCESSING

$2259 - VARIABLE-LENGTH BIT GAME PAK ROM START ADDRESS

$2300 - SUPER NES CPU FLAG READ

$2301 - SA-1 CPU FLAG READ

$2302 - H-COUNT READ

$2304 - V-COUNT READ

$2306 - ARITHMETIC RESULT [PRODUCT/QUOTIENT/ACCUMULATIVE SUM]

$230B - ARITHMETIC OVERFLOW FLAG

$230C - VARIABLE-LENGTH DATA READ PORT

$230E - VERSION CODE REGISTER (OPEN BUS)

D7 D6 D5 D4 D3 D2 D1 D0 Register
VC7 VC6 VC5 VC4 VC3 VC2 VC1 VC0 $230E
Bits Meaning
VC0 ~ VC7 SA-1 Device Version

According the SNES Development Book II, this register was supposed to hold the SA-1 chip version code, however tests made on some real carts has shown that this register in particular is actually open bus.


Memory and Bus

Memory Map

SNES Side

SA-1 Side

Open Bus Behavior

ROM

I-RAM

Write Protection

BW-RAM

Write Protection

Virtual Bitmap Memory

Super MMC

Bus Conflicts

Direct Memory Access

Character Conversion DMA

Parallel DMA

Interactions with SNES DMA

Undefined Behavior

Variable Length Bit

Fixed Mode

Automatic Mode

Mixed Mode

Arithmetic Operations

Multiplication

Division

Cumulative Sum

Parallelism and I/O

IRQ

NMI

FastROM Interactions