DSTT: Add DMA support and reduce code size (#162) Fixes #111

CHANGELOG.md

@@ -3,10 +3,12 @@
 ## [Unreleased]
 
 ### Added
+- DMA card read support for the DSTT platform - by @lifehackerhansol
 - DMA card read support for the M3DS platform - by @lifehackerhansol
 
 ### Fixed
 - DMA card read offsets for Pokemon Ranger (EU) - by @taxicat1
+- Split DSTT SD read to multiple patches to avoid running out of space - by @lifehackerhansol
 
 ## [v1.6.0] - 29 Mar 2026
 

README.md

@@ -30,7 +30,7 @@ Note that there can be some game compatibility differences between different pla
 | AKRPG         | Acekard RPG SD card                                                                            | ❌ |
 | DATEL         | DATEL devices consisting of GAMES n' MUSIC and Action Replay DS(i) Media Edition               | ❌ |
 | DSPICO        | DSpico                                                                                         | ✅ |
-| DSTT          | DSTT, SuperCard DSONE SDHC, r4isdhc.com carts 2014+, r4i-sdhc.com carts, various derivatives   | ❌ |
+| DSTT          | DSTT, SuperCard DSONE SDHC, r4isdhc.com carts 2014+, r4i-sdhc.com carts, various derivatives   | ✅ |
 | EZP           | EZ-Flash Parallel                                                                              | ❌ |
 | G003          | M3i Zero (GMP-Z003)                                                                            | ✅ |
 | ISNITRO       | Supports the IS-NITRO-EMULATOR through agb semihosting.                                        | ❌ |

arm9/source/patches/platform/dstt/DsttLoaderPlatform.cpp

@@ -190,7 +190,7 @@ bool DsttLoaderPlatform::InitializeSdCard(void)
     if (isSdhc)
     {
         sdHostSetRegister(DSTT_SD_HOST_REG_RESET | DSTT_SD_HOST_REG_CLEAN_ROM_MODE | DSTT_SD_HOST_REG_SDHC);
-        dstt_readSd_sdsc_shift = THUMB_MOVS_REG(THUMB_R7, THUMB_R0);
+        dstt_readSd_sdsc_shift = THUMB_MOVS_REG(THUMB_R6, THUMB_R0);
         dstt_writeSd_sdsc_shift = THUMB_NOP;
     }
     return true;

arm9/source/patches/platform/dstt/DsttLoaderPlatform.h

@@ -1,7 +1,10 @@
 #pragma once
 #include "../LoaderPlatform.h"
 #include "DsttReadSdPatchCode.h"
+#include "DsttReadSdDmaPatchCode.h"
 #include "DsttWriteSdPatchCode.h"
+#include "DsttSdStopTransmissionPatchCode.h"
+#include "DsttReadSdHelperPatchCode.h"
 
 /// @brief Implementation of LoaderPlatform for the DSTT flashcard
 class DsttLoaderPlatform : public LoaderPlatform
@@ -15,11 +18,30 @@ public:
             return new DsttReadSdPatchCode(patchHeap,
                 patchCodeCollection.GetOrAddSharedPatchCode([&]
                 {
-                    return new DsttReadSdStopTransmissionPatchCode(patchHeap);
+                    return new DsttSdStopTransmissionPatchCode(patchHeap);
+                }),
+                patchCodeCollection.GetOrAddSharedPatchCode([&]
+                {
+                    return new DsttReadSdHelperPatchCode(patchHeap);
                 }));
         });
     }
 
+    const IReadSectorsDmaPatchCode* CreateSdReadDmaPatchCode(PatchCodeCollection& patchCodeCollection,
+        PatchHeap& patchHeap, const void* miiCardDmaCopy32Ptr) const override
+    {
+        return patchCodeCollection.AddUniquePatchCode<DsttReadSdDmaPatchCode>(
+            patchHeap, miiCardDmaCopy32Ptr,
+                patchCodeCollection.GetOrAddSharedPatchCode([&]
+                {
+                    return new DsttSdStopTransmissionPatchCode(patchHeap);
+                }),
+                patchCodeCollection.GetOrAddSharedPatchCode([&]
+                {
+                    return new DsttReadSdHelperPatchCode(patchHeap);
+                }));
+    }
+
     const IWriteSectorsPatchCode* CreateSdWritePatchCode(
         PatchCodeCollection& patchCodeCollection, PatchHeap& patchHeap) const override
     {
@@ -35,5 +57,7 @@ public:
 
     LoaderPlatformType GetPlatformType() const override { return LoaderPlatformType::Slot1; }
 
+    bool HasDmaSdReads() const override { return true; }
+
     bool InitializeSdCard() override;
 };

arm9/source/patches/platform/dstt/DsttReadSdDmaPatchCode.h

@@ -0,0 +1,44 @@
+#pragma once
+#include "sections.h"
+#include "patches/PatchCode.h"
+#include "../IReadSectorsDmaPatchCode.h"
+#include "DsttSdStopTransmissionPatchCode.h"
+#include "DsttReadSdHelperPatchCode.h"
+
+DEFINE_SECTION_SYMBOLS(dstt_readsddma);
+
+extern "C" void dstt_readSdDma(u32 srcSector, u32 previousSrcSector, u32 dmaChannel, void* dst);
+
+extern u32 dstt_readSdDma_applySectorCommand_address;
+extern u32 dstt_readSdDma_waitDataReady_address;
+extern u32 dstt_readSdDma_stopTransmission_address;
+extern u32 dstt_readSdDma_miiCardDmaCopy32Ptr;
+
+class DsttReadSdDmaPatchCode : public PatchCode, public IReadSectorsDmaPatchCode
+{
+public:
+    DsttReadSdDmaPatchCode(PatchHeap& patchHeap, const void* miiCardDmaCopy32Ptr,
+        const DsttSdStopTransmissionPatchCode* dsttSdStopTransmissionPatchCode,
+        const DsttReadSdHelperPatchCode* dsttReadSdHelperPatchCode)
+        : PatchCode(SECTION_START(dstt_readsddma), SECTION_SIZE(dstt_readsddma), patchHeap)
+    {
+        dstt_readSdDma_miiCardDmaCopy32Ptr = (u32)miiCardDmaCopy32Ptr;
+        dstt_readSdDma_stopTransmission_address = (u32)dsttSdStopTransmissionPatchCode->GetStopTransmissionFunction();
+        dstt_readSdDma_applySectorCommand_address = (u32)dsttReadSdHelperPatchCode->GetApplySectorCommandFunction();
+        dstt_readSdDma_waitDataReady_address = (u32)dsttReadSdHelperPatchCode->GetWaitDataReadyFunction();
+        _sdReadDmaFinishFunc = (ReadSectorsDmaFinishFunc)dsttSdStopTransmissionPatchCode->GetStopTransmissionFunction();
+    }
+
+    const ReadSectorsDmaFunc GetReadSectorsDmaFunction() const override
+    {
+        return (const ReadSectorsDmaFunc)GetAddressAtTarget((void*)dstt_readSdDma);
+    }
+
+    const ReadSectorsDmaFinishFunc GetReadSectorsDmaFinishFunction() const override
+    {
+        return _sdReadDmaFinishFunc;
+    }
+
+private:
+    ReadSectorsDmaFinishFunc _sdReadDmaFinishFunc = 0;
+};

arm9/source/patches/platform/dstt/DsttReadSdDmaPatchCode.s

@@ -0,0 +1,111 @@
+.cpu arm946e-s
+.section "dstt_readsddma", "ax"
+.syntax unified
+.thumb
+
+// r0 = src sector
+// r1 = previous src sector
+// r2 = dma channel
+// r3 = dst
+.global dstt_readSdDma
+.type dstt_readSdDma, %function
+dstt_readSdDma:
+    push {r2-r7,lr}
+
+    ldr r4, =0x040001A0
+
+    movs r3, #0x80
+    strb r3, [r4,#1]
+
+    adr r2, dstt_romSettings
+    // r2 - dstt_romSettings
+    // r3 - dstt_readSdDma_applySectorCommand_address
+    // r5 - dstt_readSdDma_stopTransmission_address
+    // r6 - dstt_readSdDma_waitDataReady_address
+    // r7 - dstt_readSdDma_miiCardDmaCopy32Ptr
+    ldmia r2, {r2, r3, r5, r6, r7}
+
+    cmp r1, #0
+    beq applySector
+
+    subs r1, r0, r1
+    cmp r1, #1 // if sequential
+    beq sector_loop_sequential
+
+    blx r5 // dstt_readSdDma_stopTransmission_address
+
+applySector:
+    blx r3 // dstt_readSdDma_applySectorCommand_address
+
+    b sector_loop
+
+sector_loop_sequential:
+    // set sd host mode DSTT_MODE_RECEIVE_DATA_BLOCK_STOP_CLOCK
+    // 51 00 00 00 00 00 07 00
+    movs r1, #0x51
+    str r1, [r4, #0x8]
+    movs r1, #7
+    lsls r1, r1, #16
+    str r1, [r4, #0xC]
+
+sector_loop:
+    str r2, [r4,#4]
+
+    movs r1, #0x41
+    lsls r1, r1, #20 // r1 = 0x04100000
+
+cmd_wait_loop:
+    ldrb r3, [r4,#6]
+    lsrs r3, r3, #8
+    bcc cmd_wait_loop
+
+    ldr r3, [r1, #0x10]
+    blx r6 // dstt_readSdDma_waitDataReady_address
+
+    // previous push had r2 = dma channel, r3 = dst at top of stack
+    // pop to the correct register for miiCardDmaCopy32
+    pop {r0, r2}
+    adds r1, #0x10 // Source. r1 is 0x04100000 from the calling function
+    movs r3, #1
+    lsls r3, r3, #9 // (1 << 9) = 512 = count
+
+    blx r7 // dstt_readSdDma_miiCardDmaCopy32Ptr
+
+cmd81_poll_dma:
+    // read sd fifo
+    // 81 xx xx xx xx xx xx xx
+    // xx bytes are leftover from previous command
+    movs r1, #0x81
+    strb r1, [r4,#0x8]
+
+    movs r1, #0xC0 // select rom mode, with irq
+    strb r1, [r4,#0x1]
+    movs r1, #0xA1
+    strb r1, [r4,#7]
+
+    pop {r4-r7,pc}
+
+.balign 4
+
+dstt_romSettings:
+    .word 0xA7180000
+
+.global dstt_readSdDma_applySectorCommand_address
+dstt_readSdDma_applySectorCommand_address:
+    .word 0
+
+.global dstt_readSdDma_stopTransmission_address
+dstt_readSdDma_stopTransmission_address:
+    .word 0
+
+.global dstt_readSdDma_waitDataReady_address
+dstt_readSdDma_waitDataReady_address:
+    .word 0
+
+.global dstt_readSdDma_miiCardDmaCopy32Ptr
+dstt_readSdDma_miiCardDmaCopy32Ptr:
+    .word 0
+
+.pool
+
+.end

arm9/source/patches/platform/dstt/DsttReadSdHelperPatchCode.h

@@ -0,0 +1,34 @@
+#pragma once
+#include "sections.h"
+#include "thumbInstructions.h"
+#include "patches/PatchCode.h"
+
+DEFINE_SECTION_SYMBOLS(dstt_readsd_helper);
+
+extern "C" void dstt_readSd_applySectorCommand(void);
+extern "C" void dstt_readSd_waitDataReady(void);
+extern "C" void dstt_readSd_transferData();
+
+extern u16 dstt_readSd_sdsc_shift;
+
+class DsttReadSdHelperPatchCode : public PatchCode
+{
+public:
+    explicit DsttReadSdHelperPatchCode(PatchHeap& patchHeap)
+        : PatchCode(SECTION_START(dstt_readsd_helper), SECTION_SIZE(dstt_readsd_helper), patchHeap) { }
+
+    const void* GetApplySectorCommandFunction() const
+    {
+        return GetAddressAtTarget((void*)dstt_readSd_applySectorCommand);
+    }
+
+    const void* GetWaitDataReadyFunction() const
+    {
+        return GetAddressAtTarget((void*)dstt_readSd_waitDataReady);
+    }
+
+    const void* GetTransferDataFunction() const
+    {
+        return GetAddressAtTarget((void*)dstt_readSd_transferData);
+    }
+};

arm9/source/patches/platform/dstt/DsttReadSdHelperPatchCode.s

@@ -0,0 +1,103 @@
+.cpu arm7tdmi
+.section "dstt_readsd_helper", "ax"
+.syntax unified
+.thumb
+
+// r0 = src sector
+.global dstt_readSd_applySectorCommand
+.type dstt_readSd_applySectorCommand, %function
+dstt_readSd_applySectorCommand:
+    push {r5-r6,lr}
+
+.global dstt_readSd_sdsc_shift
+dstt_readSd_sdsc_shift:
+    lsls r6, r0, #9
+
+    // request sd read for sector 0xaabbccdd
+    // 54 aa bb cc dd 00 00 00
+    movs r5, #0x54
+    strb r5, [r4,#0x8]
+    lsrs r5, r6, #24
+    strb r5, [r4,#0x9]
+    lsrs r5, r6, #16
+    strb r5, [r4,#0xA]
+    lsrs r5, r6, #8
+    strb r5, [r4,#0xB]
+    // make sure the last 3 bytes are zero
+    movs r5, #0xFF
+    ands r6, r5
+    str r6, [r4,#0xC] // storing as little-endian puts the bottom 8 bits as first byte
+
+    pop {r5-r6,pc}
+
+.balign 4
+
+.global dstt_readSd_waitDataReady
+.type dstt_readSd_waitDataReady, %function
+dstt_readSd_waitDataReady:
+    push {r5-r7,lr}
+
+    movs r6, #0x41
+    lsls r6, r6, #20 // r6 = 0x04100000
+
+    // sd fifo full poll
+    // 80 xx xx xx xx xx xx xx
+    // xx bytes are leftover from previous command
+    movs r7, #0x80
+    strb r7, [r4,#0x8]
+
+    ldr r7, =0xA7180000
+cmd80_poll_loop:
+    str r7, [r4,#4]
+
+cmd80_wait_loop:
+    ldrb r5, [r4,#6]
+    lsrs r5, r5, #8
+    bcc cmd80_wait_loop
+    ldr r5, [r6, #0x10]
+    cmp r5, #0
+    bne cmd80_poll_loop
+
+    pop {r5-r7,pc}
+
+.balign 4
+
+// r1 = dst, will be incremented by 512
+.global dstt_readSd_transferData
+.type dstt_readSd_transferData, %function
+dstt_readSd_transferData:
+    push {r5-r7,lr}
+
+    ldr r5, =0xA7180000
+
+    movs r6, #0x41
+    lsls r6, r6, #20 // r6 = 0x04100000
+
+    // read sd fifo
+    // 81 xx xx xx xx xx xx xx
+    // xx bytes are leftover from previous command
+    movs r5, #0x81
+    strb r5, [r4,#0x8]
+    movs r5, #0xA1
+    strb r5, [r4,#7]
+
+cmd81_data_loop:
+    ldrb r5, [r4,#6]
+    lsrs r5, r5, #8 // check if data is ready
+    bcc cmd81_data_loop_check_transfer_end // if not skip reading
+
+    ldr r5, [r6, #0x10]
+    stmia r1!, {r5}
+
+cmd81_data_loop_check_transfer_end:
+    ldrb r5, [r4,#7]
+    lsrs r5, r5, #8 // check if transfer is done
+    bcs cmd81_data_loop
+
+    pop {r5-r7,pc}
+
+.balign 4
+
+.pool
+
+.end

arm9/source/patches/platform/dstt/DsttReadSdPatchCode.h

@@ -3,36 +3,30 @@
 #include "thumbInstructions.h"
 #include "patches/PatchCode.h"
 #include "../IReadSectorsPatchCode.h"
+#include "DsttSdStopTransmissionPatchCode.h"
+#include "DsttReadSdHelperPatchCode.h"
 
 DEFINE_SECTION_SYMBOLS(dstt_readsd);
-DEFINE_SECTION_SYMBOLS(dstt_readsd_stopTransmission);
 
 extern "C" void dstt_readSd(u32 srcSector, void* dst, u32 sectorCount);
-extern "C" void dstt_stopTransmission();
 
+extern u32 dstt_readSd_applySectorCommand_address;
+extern u32 dstt_waitDataReady_address;
+extern u32 dstt_transferData_address;
 extern u32 dstt_stopTransmission_address;
-extern u16 dstt_readSd_sdsc_shift;
-
-class DsttReadSdStopTransmissionPatchCode : public PatchCode
-{
-public:
-    explicit DsttReadSdStopTransmissionPatchCode(PatchHeap& patchHeap)
-        : PatchCode(SECTION_START(dstt_readsd_stopTransmission), SECTION_SIZE(dstt_readsd_stopTransmission), patchHeap) { }
-
-    const void* GetStopTransmissionFunction() const
-    {
-        return GetAddressAtTarget((void*)dstt_stopTransmission);
-    }
-};
 
 class DsttReadSdPatchCode : public PatchCode, public IReadSectorsPatchCode
 {
 public:
     explicit DsttReadSdPatchCode(PatchHeap& patchHeap,
-        const DsttReadSdStopTransmissionPatchCode* dsttReadSdStopTransmissionPatchCode)
+        const DsttSdStopTransmissionPatchCode* dsttSdStopTransmissionPatchCode,
+        const DsttReadSdHelperPatchCode* dsttReadSdHelperPatchCode)
         : PatchCode(SECTION_START(dstt_readsd), SECTION_SIZE(dstt_readsd), patchHeap)
         {
-            dstt_stopTransmission_address = (u32)dsttReadSdStopTransmissionPatchCode->GetStopTransmissionFunction();
+            dstt_readSd_applySectorCommand_address = (u32)dsttReadSdHelperPatchCode->GetApplySectorCommandFunction();
+            dstt_stopTransmission_address = (u32)dsttSdStopTransmissionPatchCode->GetStopTransmissionFunction();
+            dstt_waitDataReady_address = (u32)dsttReadSdHelperPatchCode->GetWaitDataReadyFunction();
+            dstt_transferData_address = (u32)dsttReadSdHelperPatchCode->GetTransferDataFunction();
         }
 
     const ReadSectorsFunc GetReadSectorsFunction() const override

arm9/source/patches/platform/dstt/DsttReadSdPatchCode.s

@@ -11,27 +11,11 @@
 dstt_readSd:
     push {r4-r7,lr}
 
-.global dstt_readSd_sdsc_shift
+    ldr r3, =0xA7180000
-dstt_readSd_sdsc_shift:
+    ldr r4, =0x040001A0
-    lsls r7, r0, #9
 
-    adr r0, dstt_stopTransmission_address
+    ldr r7, dstt_readSd_applySectorCommand_address
-    ldmia r0, {r0, r3, r4}
+    bl blx_r7
-
-    // request sd read for sector 0xaabbccdd
-    // 54 aa bb cc dd 00 00 00
-    movs r5, #0x54
-    strb r5, [r4,#0x8]
-    lsrs r5, r7, #24
-    strb r5, [r4,#0x9]
-    lsrs r5, r7, #16
-    strb r5, [r4,#0xA]
-    lsrs r5, r7, #8
-    strb r5, [r4,#0xB]
-    // make sure the last 3 bytes are zero
-    movs r5, #0xFF
-    ands r7, r5
-    str r7, [r4,#0xC] // storing as little-endian puts the bottom 8 bits as first byte
 
     movs r7, #0x80
     strb r7, [r4,#1]
@@ -48,42 +32,11 @@ cmd54_wait_loop:
     bcc cmd54_wait_loop
 
     ldr r5, [r6, #0x10]
-    // sd fifo full poll
+    ldr r7, dstt_waitDataReady_address
-    // 80 xx xx xx xx xx xx xx
+    bl blx_r7
-    // xx bytes are leftover from previous command
-    strb r7, [r4,#0x8]
 
-cmd80_poll_loop:
+    ldr r7, dstt_transferData_address
-    str r3, [r4,#4]
+    bl blx_r7
-
-cmd80_wait_loop:
-    ldrb r5, [r4,#6]
-    lsrs r5, r5, #8
-    bcc cmd80_wait_loop
-    ldr r5, [r6, #0x10]
-    cmp r5, #0
-    bne cmd80_poll_loop
-
-    // read sd fifo
-    // 81 xx xx xx xx xx xx xx
-    // xx bytes are leftover from previous command
-    movs r5, #0x81
-    strb r5, [r4,#0x8]
-    movs r5, #0xA1
-    strb r5, [r4,#7]
-
-cmd81_data_loop:
-    ldrb r5, [r4,#6]
-    lsrs r5, r5, #8 // check if data is ready
-    bcc cmd81_data_loop_check_transfer_end // if not skip reading
-
-    ldr r5, [r6, #0x10]
-    stmia r1!, {r5}
-
-cmd81_data_loop_check_transfer_end:
-    ldrb r5, [r4,#7]
-    lsrs r5, r5, #8 // check if transfer is done
-    bcs cmd81_data_loop
 
     subs r2, #1
     beq stop_transmission
@@ -99,77 +52,31 @@ cmd81_data_loop_check_transfer_end:
     b sector_loop
 
 stop_transmission:
-    bx r0
+    ldr r7, dstt_stopTransmission_address
+    bl blx_r7
+    pop {r4-r7,pc}
+
+blx_r7:
+    bx r7
 
 .balign 4
 
+.global dstt_readSd_applySectorCommand_address
+dstt_readSd_applySectorCommand_address:
+    .word 0
+
+.global dstt_waitDataReady_address
+dstt_waitDataReady_address:
+    .word 0
+
+.global dstt_transferData_address
+dstt_transferData_address:
+    .word 0
+
 .global dstt_stopTransmission_address
 dstt_stopTransmission_address:
     .word 0
 
-settings:
-    .word 0xA7180000
-
-regbase:
-    .word 0x040001A0
-
 .pool
 
-.section "dstt_readsd_stopTransmission", "ax"
+.end
-.thumb
-.global dstt_stopTransmission
-.type dstt_stopTransmission, %function
-dstt_stopTransmission:
-    // send SD_CMD12_STOP_TRANSMISSION
-
-    // set sd host mode DSTT_MODE_SDCMD_RESPONSE_32BIT, SD_CMD12_STOP_TRANSMISSION
-    // 51 00 00 00 00 0C 01 00
-    movs r5, #0x51
-    str r5, [r4,#0x8]
-    ldr r5,= 0x00010C00
-    str r5, [r4,#0xC]
-    str r3, [r4,#4]
-
-cmd51_1_wait_loop:
-    ldrb r5, [r4,#6]
-    lsrs r5, r5, #8
-    bcc cmd51_1_wait_loop
-    ldr r5, [r6, #0x10]
-
-    // sd busy poll
-    // 50 xx xx xx xx xx xx xx
-    // xx bytes are leftover from previous command
-    movs r5, #0x50
-    strb r5, [r4,#0x8]
-
-cmd50_poll_loop:
-    str r3, [r4,#4]
-
-cmd50_wait_loop:
-    ldrb r5, [r4,#6]
-    lsrs r5, r5, #8
-    bcc cmd50_wait_loop
-    ldr r5, [r6, #0x10]
-    cmp r5, #0
-    bne cmd50_poll_loop
-
-    // read sd response
-    // 52 xx xx xx xx xx xx xx
-    // xx bytes are leftover from previous command
-    movs r5, #0x52
-    strb r5, [r4,#0x8]
-    str r3, [r4,#4]
-
-cmd52_wait_loop:
-    ldrb r5, [r4,#6]
-    lsrs r5, r5, #8
-    bcc cmd52_wait_loop
-    ldr r5, [r6, #0x10]
-
-    pop {r4-r7,pc}
-
-.balign 4
-
-.pool
-
-.end

arm9/source/patches/platform/dstt/DsttSdStopTransmissionPatchCode.h

@@ -0,0 +1,20 @@
+#pragma once
+#include "sections.h"
+#include "thumbInstructions.h"
+#include "patches/PatchCode.h"
+
+DEFINE_SECTION_SYMBOLS(dstt_sdstoptransmission);
+
+extern "C" void dstt_sdStopTransmission();
+
+class DsttSdStopTransmissionPatchCode : public PatchCode
+{
+public:
+    explicit DsttSdStopTransmissionPatchCode(PatchHeap& patchHeap)
+        : PatchCode(SECTION_START(dstt_sdstoptransmission), SECTION_SIZE(dstt_sdstoptransmission), patchHeap) { }
+
+    const void* GetStopTransmissionFunction() const
+    {
+        return GetAddressAtTarget((void*)dstt_sdStopTransmission);
+    }
+};

arm9/source/patches/platform/dstt/DsttSdStopTransmissionPatchCode.s

@@ -0,0 +1,73 @@
+.cpu arm7tdmi
+.syntax unified
+.thumb
+
+.section "dstt_sdstoptransmission", "ax"
+.global dstt_sdStopTransmission
+.type dstt_sdStopTransmission, %function
+dstt_sdStopTransmission:
+    // send SD_CMD12_STOP_TRANSMISSION
+    push {r3-r6,lr}
+
+    ldr r3, =0xA7180000
+    ldr r4, =0x040001A0
+
+    // select rom mode, without irq
+    // the caller may not have ensured this is set
+    movs r6, #0x80
+    strb r6, [r4,#1]
+
+    // set sd host mode DSTT_MODE_SDCMD_RESPONSE_32BIT, SD_CMD12_STOP_TRANSMISSION
+    // 51 00 00 00 00 0C 01 00
+    movs r5, #0x51
+    str r5, [r4,#0x8]
+    ldr r5,= 0x00010C00
+    str r5, [r4,#0xC]
+    str r3, [r4,#0x4]
+
+    movs r6, #0x41
+    lsls r6, r6, #20 // r6 = 0x04100000
+
+cmd51_1_wait_loop:
+    ldrb r5, [r4,#6]
+    lsrs r5, r5, #8
+    bcc cmd51_1_wait_loop
+    ldr r5, [r6, #0x10]
+
+    // sd busy poll
+    // 50 xx xx xx xx xx xx xx
+    // xx bytes are leftover from previous command
+    movs r5, #0x50
+    strb r5, [r4,#0x8]
+
+cmd50_poll_loop:
+    str r3, [r4,#4]
+
+cmd50_wait_loop:
+    ldrb r5, [r4,#6]
+    lsrs r5, r5, #8
+    bcc cmd50_wait_loop
+    ldr r5, [r6, #0x10]
+    cmp r5, #0
+    bne cmd50_poll_loop
+
+    // read sd response
+    // 52 xx xx xx xx xx xx xx
+    // xx bytes are leftover from previous command
+    movs r5, #0x52
+    strb r5, [r4,#0x8]
+    str r3, [r4,#4]
+
+cmd52_wait_loop:
+    ldrb r5, [r4,#6]
+    lsrs r5, r5, #8
+    bcc cmd52_wait_loop
+    ldr r5, [r6, #0x10]
+
+    pop {r3-r6,pc}
+
+.balign 4
+
+.pool
+
+.end