Add support for Slot 2 flashcarts using Compact Flash (#84)

- Supercard CF (SUPERCARDCF)
- GBA Media Player CF (MPCF)
- M3 Adapter CF (M3CF)
- Max Media Dock CF (MMCF)

arm9/source/patches/platform/compactflash-common/CompactFlashCommonLoaderPlatform.cpp

@@ -0,0 +1,66 @@
+#include "common.h"
+#include <libtwl/mem/memExtern.h>
+#include "CompactFlashCommonLoaderPlatform.h"
+
+static constexpr int CF_CARD_TIMEOUT = 10000000;
+static constexpr int CF_STS_READY = 0x40;
+static constexpr int CF_STS_DSC = 0x10;
+static constexpr int CF_STS_BUSY = 0x80;
+
+bool CompactFlashCommonLoaderPlatform::InitializeSdCard()
+{
+    u32 oldMemCnt = REG_EXMEMCNT;
+    mem_setGbaCartridgeRomWaits(EXMEMCNT_SLOT2_ROM_WAIT1_10, EXMEMCNT_SLOT2_ROM_WAIT2_6);
+    SetCardLocked(false);
+    auto res = InitializeCfCard();
+    SetCardLocked(true);
+    REG_EXMEMCNT = oldMemCnt;
+    return res;
+}
+
+static bool waitAvailableForCommands(const cf_registers_t& registers)
+{
+    // wait for card to finish previous commands
+    for (int i = 0; i < CF_CARD_TIMEOUT; i++)
+    {
+        if ((*registers.command & CF_STS_BUSY) == 0)
+        {
+            break;
+        }
+    }
+
+    // wait for card to be ready for new commands
+    for (int i = 0; i < CF_CARD_TIMEOUT; i++)
+    {
+        if ((*registers.command & (CF_STS_READY | CF_STS_DSC)) != 0)
+        {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+bool CompactFlashCommonLoaderPlatform::InitializeCfCard()
+{
+    const auto& registers = GetCfRegisters();
+    if (!waitAvailableForCommands(registers))
+    {
+        return false;
+    }
+    // Check that the registers are writable and hold the values we set
+    u16 temp = *registers.lba1;
+    *registers.lba1 = (~temp & 0xFF);
+    temp = (~temp & 0xFF);
+    if (*registers.lba1 != temp)
+    {
+        return false;
+    }
+
+    *registers.lba1 = 0xAA55;
+    if (*registers.lba1 == 0xAA55)
+    {
+        return false;
+    }
+    return true;
+}