read_external function

snes-core/src/cpu/bus.rs

@@ -56,6 +56,22 @@ impl Bus {
         }
     }
 
+    /// This function is meant to be used by external parts of the code,
+    /// for example, to render register info without mutating them
+    pub fn read_external(&self, address: u32) -> u8 {
+        let section = Bus::map_address(address);
+        match section {
+            MemoryMap::WRAM => self.read_wram(address),
+            MemoryMap::PPU => self.ppu.registers.read_external(address as u16),
+            MemoryMap::CPU => self.internal_registers.read_external(
+                address as u16,
+                &self.ppu.registers,
+            ),
+            MemoryMap::Joypad => 0x00,  // TODO: Placeholder
+            MemoryMap::Cartridge => self.rom.read(address),
+        }
+    }
+
     pub fn read(&mut self, address: u32) -> u8 {
         let section = Bus::map_address(address);
         match section {

snes-core/src/cpu/internal_registers.rs

@@ -24,18 +24,31 @@ impl InternalRegisters {
         self.registers[(address - INTERNAL_REGISTERS_ADDRESS) as usize] = value
     }
 
-    pub fn read(&self, address: u16, ppu_registers: &mut PPURegisters) -> u8 {
+    pub fn read_external(&self, address: u16, ppu_registers: &PPURegisters) -> u8 {
         match address {
             RDNMI => self.read_vblank_nmi(ppu_registers),
             _ => self._read(address),
         }
     }
 
+    pub fn read(&self, address: u16, ppu_registers: &mut PPURegisters) -> u8 {
+        match address {
+            RDNMI => self.read_vblank_nmi_mut(ppu_registers),
+            _ => self._read(address),
+        }
+    }
+
     pub fn write(&mut self, address: u16, value: u8) {
         self._write(address, value);
     }
 
-    fn read_vblank_nmi(&self, ppu_registers: &mut PPURegisters) -> u8 {
+    fn read_vblank_nmi(&self, ppu_registers: &PPURegisters) -> u8 {
+        let byte = self._read(RDNMI);
+        let result = (byte & 0x7F) | ((ppu_registers.vblank_nmi as u8) << 7);
+        result
+    }
+
+    fn read_vblank_nmi_mut(&self, ppu_registers: &mut PPURegisters) -> u8 {
         let byte = self._read(RDNMI);
         // When register is read, bit 7 is cleared
         let result = (byte & 0x7F) | ((ppu_registers.vblank_nmi as u8) << 7);

snes-core/src/ppu/registers.rs

@@ -164,6 +164,10 @@ impl PPURegisters {
         self.data[(address as usize) - 0x2100] = value;
     }
 
+    pub fn read_external(&self, address: u16) -> u8 {
+        self._read(address)
+    }
+
     pub fn read(&mut self, address: u16) -> u8 {
         let result = self._read(address);
         match address {