--- nono/vm/sysport.cpp	2026/04/29 17:05:09	1.1.1.8
+++ nono/vm/sysport.cpp	2026/04/29 17:05:13	1.1.1.9
@@ -12,9 +12,11 @@
 #include "keyboard.h"
 #include "mpu.h"
 #include "nmi.h"
+#include "power.h"
 #include "ram.h"
 #include "romimg_x68k.h"
 #include "sram.h"
+#include <array>
 
 // グローバル参照用
 SysportDevice *gSysport;
@@ -43,6 +45,8 @@ SysportDevice::ResetHard(bool poweron)
 	sysport.ram_wait = 0;
 	sysport.rom_wait = 0;
 	sysport.key_ctrl = false;
+	sysport.pwoff_count = 0;
+	gPower->SetSystemPowerOn(true);
 }
 
 uint64
@@ -82,7 +86,7 @@ SysportDevice::Read(uint32 offset)
 	 default:
 		__unreachable();
 	}
-	putlog(1, "$%06X -> $%02x", gMPU->GetPaddr(), data);
+	putlog(2, "$%06x -> $%02x", gMPU->GetPaddr(), data);
 	return data;
 }
 
@@ -102,7 +106,7 @@ SysportDevice::Write(uint32 offset, uint
 		data &= 0x0e;
 		// bit1
 		if ((data & 0x02)) {
-			putlog(0, "$E8E007 未サポート書き込み $%02x", data);
+			putlog(0, "$e8e007 <- $%02x (HRL NOT IMPLEMENTED)", data);
 		}
 		// bit2: NMI リセット
 		if ((data & 0x04)) {
@@ -141,8 +145,25 @@ SysportDevice::Write(uint32 offset, uint
 		break;
 
 	 case SYSPORT::POWEROFF:
-		putlog(0, "$e8e00f (POWEROFF) 未サポート書き込み %02x", data);
+	 {
+		static const std::array<uint8, 3> sig { 0x00, 0x0f, 0x0f };
+
+		assertmsg(sysport.pwoff_count < sig.size(),
+			"sysport.pwoff_count=%d", sysport.pwoff_count);
+		if (data == sig[sysport.pwoff_count]) {
+			sysport.pwoff_count++;
+		} else {
+			sysport.pwoff_count = 0;
+		}
+		putlog(2, "$e8e00f (POWEROFF) <- %02x (count=%d)",
+			data, sysport.pwoff_count);
+		if (sysport.pwoff_count == sig.size()) {
+			// pwoff_count はここではクリアせず、電源オン時に再初期化する。
+			putlog(1, "$e8e00f (POWEROFF) Power Off");
+			gPower->SetSystemPowerOn(false);
+		}
 		break;
+	 }
 
 	 default:
 		__unreachable();