From 4bf12db91feb5db98d65b518dbad0c1a8c6748df Mon Sep 17 00:00:00 2001
From: Miquel Sabaté Solà <mssola@mssola.com>
Date: Tue, 6 Oct 2026 17:15:16 +0200
Subject: readrom: add support for default expansion device
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The 15th byte from the NES 2.0 header was wilfully ignored, but it can
be relevant to the end user. Hence, add support for it in the 'header'
library, and add the frontend code into 'readrom'.

The point is not to support every single thing out there, but I have
added the stuff that I thought was most relevant, and we can add more
items to it whenever the need appears.

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
---
 crates/readrom/src/main.rs | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

(limited to 'crates/readrom')

diff --git a/crates/readrom/src/main.rs b/crates/readrom/src/main.rs
index f7411e3..d3701d0 100644
--- a/crates/readrom/src/main.rs
+++ b/crates/readrom/src/main.rs
@@ -175,47 +175,50 @@ fn print_header(header: &Header) {
     println!("Header:");
 
     match header.kind {
-        Kind::INes => println!("  Kind:\t\t\tiNES"),
-        Kind::Nes20 => println!("  Kind:\t\t\tNES 2.0"),
+        Kind::INes => println!("  Kind:\t\t\t\tiNES"),
+        Kind::Nes20 => println!("  Kind:\t\t\t\tNES 2.0"),
     }
 
     println!(
-        "  PRG ROM size:\t\t{} bytes ({}KB)",
+        "  PRG ROM size:\t\t\t{} bytes ({}KB)",
         header.prg_rom_size * 16 * 1024,
         header.prg_rom_size * 16
     );
     println!(
-        "  CHR ROM size:\t\t{} bytes ({}KB)",
+        "  CHR ROM size:\t\t\t{} bytes ({}KB)",
         header.chr_rom_size * 8 * 1024,
         header.chr_rom_size * 8
     );
 
     if let Some(def) = &header.prg_ram_definition {
         println!(
-            "  PRG-RAM size:\t\t{} bytes ({}KB); {}",
+            "  PRG-RAM size:\t\t\t{} bytes ({}KB); {}",
             def.size,
             def.size / 1024,
             def.kind
         );
     } else if header.has_persistent_memory {
-        println!("  PRG-RAM size:\t\t8192 bytes (8KB)");
+        println!("  PRG-RAM size:\t\t\t8192 bytes (8KB)");
     }
 
     if let Some(def) = &header.chr_ram_definition {
         println!(
-            "  CHR-RAM size:\t\t{} bytes ({}KB); {}",
+            "  CHR-RAM size:\t\t\t{} bytes ({}KB); {}",
             def.size,
             def.size / 1024,
             def.kind
         );
     }
 
-    println!("  Mapper:\t\t{}", header.mapper);
+    println!("  Mapper:\t\t\t{}", header.mapper);
     println!(
-        "  Mirroring:\t\t{}",
+        "  Mirroring:\t\t\t{}",
         capitalize(header.nametable_arrangement.mirroring())
     );
-    println!("  CPU/PPU timing:\t{}", header.timing);
+    println!("  CPU/PPU timing:\t\t{}", header.timing);
+    if let Some(ded) = header.default_expansion_device.as_ref() {
+        println!("  Default Expansion Device:\t{}", ded);
+    }
 }
 
 fn print_vectors(addrs: &[u8]) {
@@ -226,15 +229,15 @@ fn print_vectors(addrs: &[u8]) {
     }
 
     println!(
-        "  NMI:\t\t\t{:#04x}",
+        "  NMI:\t\t\t\t{:#04x}",
         u16::from_le_bytes([addrs[0], addrs[1]])
     );
     println!(
-        "  Reset:\t\t{:#04x}",
+        "  Reset:\t\t\t{:#04x}",
         u16::from_le_bytes([addrs[2], addrs[3]])
     );
     println!(
-        "  IRQ:\t\t\t{:#04x}",
+        "  IRQ:\t\t\t\t{:#04x}",
         u16::from_le_bytes([addrs[4], addrs[5]])
     );
 }
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