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86 lines
1.6 KiB
ArmAsm
86 lines
1.6 KiB
ArmAsm
.cpu arm7tdmi
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.section "writesave", "ax"
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.syntax unified
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.thumb
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// r1 = memory src
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// r2 = save dst
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// r3 = byte length
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.global writesave_asm
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.type writesave_asm, %function
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writesave_asm:
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push {r4,r5,r6,r7,lr}
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movs r4, r3 // remaining bytes
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movs r5, r2
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movs r6, r1
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1:
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movs r0, r5 // will be rounded down by function
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ldr r3, writesave_save_offset_to_sd_sector_asm_address
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bl blx_r3
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cmp r0, #0
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beq end // out of bounds
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push {r0}
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ldr r1, writesave_tmpBufferPtr
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movs r2, #1 // single sector
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lsls r7, r2, #9 // 512
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ldr r3, writesave_sdread_asm_address
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bl blx_r3
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// copy bytes
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lsls r2, r5, #23
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lsrs r2, r2, #23 // r2 = byte offset in sector
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subs r0, r6, r2
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subs r7, r7, r2 // remaining in sector
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cmp r7, r4 // if remaining in sector > requested read length
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bls 2f
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movs r7, r4 // clamp to requested read length
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2:
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subs r4, r7
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adds r5, r7
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adds r6, r7
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ldr r1, writesave_tmpBufferPtr
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3:
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ldrb r3, [r0, r2]
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strb r3, [r1, r2]
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adds r2, #1
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subs r7, #1
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bne 3b
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pop {r0}
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movs r2, #1 // single sector
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ldr r3, writesave_sdwrite_asm_address
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bl blx_r3
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cmp r4, #0
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bne 1b
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end:
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pop {r4,r5,r6,r7,pc}
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blx_r3:
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bx r3
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.balign 4
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.global writesave_tmpBufferPtr
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writesave_tmpBufferPtr:
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.word 0
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.global writesave_save_offset_to_sd_sector_asm_address
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writesave_save_offset_to_sd_sector_asm_address:
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.word 0
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.global writesave_sdread_asm_address
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writesave_sdread_asm_address:
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.word 0
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.global writesave_sdwrite_asm_address
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writesave_sdwrite_asm_address:
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.word 0
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.pool
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.end |