Support little endian system ROM files

Author: Stovent

src/CDI/CDI.cpp

@@ -3,12 +3,12 @@
 
 /** \brief Creates a new CD-i instance.
  * \param board The type of board to use.
- * \param systemBios System BIOS data.
+ * \param systemBios System BIOS data (in big endian format).
  * \param nvram The initial state of the NVRAM, or an empty span to use a clean NVRAM.
  * \param config The player configuration.
  * \param callbacks The user callbacks to use.
  * \param disc The disc to load (optional).
- * \return nullptr if it failed to initialize the new CDI.
+ * \return nullptr if the BIOS is not supported or if it failed to auto detect the CDI BIOS type.
  *
  * If \p board is Boards::AutoDetect, then the board type will be guessed from the BIOS data.
  * It may not be accurate so when possible, consider providing yourself the board type.

src/CeDImu.cpp

@@ -1,6 +1,7 @@
 #include "CeDImu.hpp"
 #include "GUI/MainFrame.hpp"
 #include "CDI/CDI.hpp"
+#include "CDI/common/utils.hpp"
 #include "CDI/OS9/SystemCalls.hpp"
 
 #include <wx/image.h>
@@ -59,6 +60,14 @@ int CeDImu::OnExit()
     return 0;
 }
 
+/** \brief Swaps each odd and even bytes in the given buffer. */
+static constexpr void swapWords(std::span<uint8_t> data) noexcept
+{
+    assert(isEven(data.size()));
+    for(size_t i = 0; i < data.size(); i += 2)
+        std::swap(data[i], data[i + 1]);
+}
+
 bool CeDImu::InitCDI(const Config::BiosConfig& biosConfig)
 {
     {
@@ -80,6 +89,8 @@ bool CeDImu::InitCDI(const Config::BiosConfig& biosConfig)
 
     std::unique_ptr<uint8_t[]> bios = std::make_unique<uint8_t[]>(biosSize);
     biosFile.read(reinterpret_cast<char*>(bios.get()), biosSize);
+    if(biosConfig.littleEndianBios)
+        swapWords({bios.get(), biosSize});
 
     std::unique_ptr<uint8_t[]> nvramBuffer = nullptr;
     m_biosName = biosConfig.name;

src/Config.cpp

@@ -14,6 +14,7 @@ const BiosConfig defaultBiosConfig {
     .boardType = Boards::AutoDetect,
     .PAL = false,
     .has32KbNvram = false,
+    .littleEndianBios = false,
 };
 
 // Disc
@@ -91,6 +92,9 @@ bool loadConfig()
 
         if(!conf.Read("has32KbNvram", &val)) return false;
         entry.has32KbNvram = val;
+
+        if(!conf.Read("littleEndianBios", &val)) return false;
+        entry.littleEndianBios = val;
     }
 
     return true;
@@ -130,6 +134,7 @@ bool saveConfig()
         if(!conf.Write("boardType", static_cast<int>(entry.boardType))) return false;
         if(!conf.Write("PAL", entry.PAL)) return false;
         if(!conf.Write("has32KbNvram", entry.has32KbNvram)) return false;
+        if(!conf.Write("littleEndianBios", entry.littleEndianBios)) return false;
     }
 
     return conf.Flush(); // Technically it saves twice, here and in the dtor, but np I hope.

src/Config.hpp

@@ -19,6 +19,7 @@ struct BiosConfig
     Boards boardType;
     bool PAL;
     bool has32KbNvram;
+    bool littleEndianBios;
 };
 
 extern const BiosConfig defaultBiosConfig;

src/GUI/SettingsFrame.cpp

@@ -137,12 +137,14 @@ SettingsFrame::SettingsFrame(MainFrame* parent)
         boardChoiceSizer->Add(m_boardChoice, wxSizerFlags(1).Expand());
         boardChoiceSizer->Add(boardChoiceText);
 
-        // PAL and NVRAM check boxes
+        // PAL, NVRAM and little endian check boxes
         m_palCheckBox = new wxCheckBox(biosConfigPage, wxID_ANY, "PAL");
         m_nvramCheckBox = new wxCheckBox(biosConfigPage, wxID_ANY, "32KB NVRAM");
+        m_littleEndianCheckBox = new wxCheckBox(biosConfigPage, wxID_ANY, "Little endian");
         wxBoxSizer* checkBoxSizer = new wxBoxSizer(wxHORIZONTAL);
         checkBoxSizer->Add(m_palCheckBox, wxSizerFlags(1).Border());
         checkBoxSizer->Add(m_nvramCheckBox, wxSizerFlags(1).Border());
+        checkBoxSizer->Add(m_littleEndianCheckBox, wxSizerFlags(1).Border());
 
         // Initial timestamp
         m_initialTime = new wxTextCtrl(biosConfigPage, wxID_ANY);
@@ -339,6 +341,7 @@ void SettingsFrame::LoadSelection()
     m_boardChoice->SetSelection(static_cast<int>(config.boardType));
     m_palCheckBox->SetValue(config.PAL);
     m_nvramCheckBox->SetValue(config.has32KbNvram);
+    m_littleEndianCheckBox->SetValue(config.littleEndianBios);
 }
 
 void SettingsFrame::SaveSelection()
@@ -354,6 +357,7 @@ void SettingsFrame::SaveSelection()
     config.boardType = static_cast<Boards>(m_boardChoice->GetSelection());
     config.PAL = m_palCheckBox->GetValue();
     config.has32KbNvram = m_nvramCheckBox->GetValue();
+    config.littleEndianBios = m_littleEndianCheckBox->GetValue();
 }
 
 void SettingsFrame::CheckControls()
@@ -367,4 +371,5 @@ void SettingsFrame::CheckControls()
     m_boardChoice->Enable(enable);
     m_palCheckBox->Enable(enable);
     m_nvramCheckBox->Enable(enable);
+    m_littleEndianCheckBox->Enable(enable);
 }

src/GUI/SettingsFrame.hpp

@@ -31,6 +31,7 @@ class SettingsFrame : public wxFrame
     wxChoice* m_boardChoice;
     wxCheckBox* m_palCheckBox;
     wxCheckBox* m_nvramCheckBox;
+    wxCheckBox* m_littleEndianCheckBox;
     wxTextCtrl* m_initialTime;
 
     int m_keyUp;