msx_dsk.cpp: Attempt to more strongly identify MSX-DOS disk images

ajrhacker · Feb 24, 2024 · d3c81ca · d3c81ca
1 parent d1501f2
commit d3c81ca
Show file tree

Hide file tree

Showing 2 changed files with 34 additions and 1 deletion.
diff --git a/src/lib/formats/msx_dsk.cpp b/src/lib/formats/msx_dsk.cpp
@@ -1,5 +1,5 @@
 // license:BSD-3-Clause
-// copyright-holders:Olivier Galibert
+// copyright-holders:Olivier Galibert, AJR
 /*********************************************************************
 
     formats/msx_dsk.cpp
@@ -10,6 +10,10 @@
 
 #include "msx_dsk.h"
 
+#include "ioprocs.h"
+#include <cstring>
+
+
 //msx_format::msx_format() : wd177x_format(formats)
 msx_format::msx_format() : upd765_format(formats)
 {
@@ -66,4 +70,31 @@ const msx_format::format msx_format::formats[] = {
 	{}
 };
 
+int msx_format::identify(util::random_read &io, uint32_t form_factor, const std::vector<uint32_t> &variants) const
+{
+	int result = upd765_format::identify(io, form_factor, variants);
+
+	// Attempt to confirm some typical elements of MSX-DOS boot sectors
+	if(result & FIFID_SIZE) {
+		std::uint8_t sector0[0x100];
+		std::size_t actual;
+		// First byte of any bootable disk must be either EB or E9
+		if(!io.read_at(0, sector0, 0x100, actual) && actual == 0x100 && (sector0[0] & 0xfd) == 0xe9) {
+			// Z80 boot code is entered at offset 1E
+			if(sector0[0x1e] == 0xc9) {
+				// No actual boot code, so check for magic OEM name instead
+				if(!std::memcmp(&sector0[3], u8"-NO$MSX-", 8))
+					result |= FIFID_STRUCT;
+			} else if(sector0[0x1e] == 0xd0 || (sector0[0x1e] == 0x18 && sector0[0x1f] == 0x10)) {
+				int i = sector0[0x1e] == 0x18 ? 0x41 : 0x2f;
+				int j = sector0[i] + 1;
+				if(j <= 0x100 - (8+3) && !std::memcmp(&sector0[j], u8"MSXDOS  SYS", 8+3))
+					result |= FIFID_STRUCT;
+			}
+		}
+	}
+
+	return result;
+}
+
 const msx_format FLOPPY_MSX_FORMAT;
diff --git a/src/lib/formats/msx_dsk.h b/src/lib/formats/msx_dsk.h
@@ -23,6 +23,8 @@ class msx_format: public upd765_format
 	virtual const char *description() const noexcept override;
 	virtual const char *extensions() const noexcept override;
 
+	virtual int identify(util::random_read &io, uint32_t form_factor, const std::vector<uint32_t> &variants) const override;
+
 private:
 	static const format formats[];
 };