EarthBound/ASM/SRAM Routines

SRAM Routines
Game	EarthBound
Start Address	0x2F07A9
End Address	0x2F0E3C
Total Length	1684 bytes (0x0694)
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$ef05a9-$ef062f: Reset SRAM Block

Zeroes out an entire 0x500 block of SRAM and then rewrites the block signature ("HAL Laboratory, inc.", loaded from ROM at address $ef0591).

Inputs

• accumulator: SRAM block idx (0-5)

$ef0630-$ef0682: Validate SRAM Block Signature

Checks if the 0x500 block of SRAM begins with the expected block signature ("HAL Laboratory, inc.", loaded from ROM at address $ef0591). If the signature does not match the expectation, the block is reset via a call to $ef05a9.

Inputs

• accumulator: SRAM block idx (0-5)

Outputs

• accumulator: 0001 if the block was reset. Otherwise 0000.

$ef0683-$ef06a1: Validate All SRAM Block Signature

Checks all 0x500 blocks of SRAM to confirm they each begin with the expected block signature ("HAL Laboratory, inc.", loaded from ROM at address $ef0591), resetting any blocks as needed. Implemented via a trivial for loop and calls to $ef0630.

$ef06a2-$ef0733: Copy SRAM Block

Copies the entire contents of one 0x500 block of SRAM, overwriting another block. Implemented via a simple call to memcpy ($c08eed).

Inputs

• accumulator: Destination SRAM block idx (0-5)
• x: Source SRAM block idx (0-5)

$ef0734-$ef077a: Calculate SRAM Block Checksum 1

Calculates a checksum for the data contents of one 0x500 block of SRAM. (The checksum does not cover the block signature or checksums.)

Checksum 1 is calculated by adding together all bytes of the data contents.

Inputs

• accumulator: SRAM block idx (0-5)

Outputs

• accumulator: Checksum value

$ef077b-$ef07bf: Calculate SRAM Block Checksum 2

Calculates a checksum for the data contents of one 0x500 block of SRAM. (The checksum does not cover the block signature or checksums.)

Checksum 2 is calculated by XORing every 2-byte short of the data contents.

Inputs

• accumulator: SRAM block idx (0-5)

Outputs

• accumulator: Checksum value

$ef07c0-$ef0824: Validate SRAM Block Checksums

Checks if the checksums stored in one 0x500 block of SRAM are consistent with the data contents of the block. Calculates the expected checksums via calls to $ef0734 and $ef077b.

Inputs

• accumulator: SRAM block idx (0-5)

Outputs

• accumulator: 0000 on consistent checksums. ffff if inconsistent.

$ef0825-$ef088e: Validate Save Slot Checksums

Validates the checksums stored in two 0x500 blocks of SRAM, redundantly storing a single save game slot, via calls to $ef07c0. Inconsistent blocks are reset via a call to $ef05a9, and if an inconsistency is found in only one block, the good block is copied over the bad block via a call to $ef06a2.

Inputs

• accumulator: Save slot idx (0-2)

$ef0c15-$ef0c3c: Copy Save Slot

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