diff --git a/src/memory/io.rs b/src/memory/io.rs
index 4acf357..8b5afca 100644
--- a/src/memory/io.rs
+++ b/src/memory/io.rs
@@ -156,10 +156,12 @@ pub trait BusAux: BusIO {
         self.read(0x147)
     }
 
+    /// Gets the size of the cartridge ROM (in 0x4000 byte banks)
     fn romsize(&self) -> Option<usize> {
         self.read(0x148).map(|s| 1usize.wrapping_shl(s as u32 + 1))
     }
 
+    /// Gets the size of the cartridge RAM (in 0x2000 byte banks)
     fn ramsize(&self) -> Option<usize> {
         self.read(0x149).map(|s| match s {
             0x02 => 1,