Note about the black swirl

src/mame/machine/dc.c

@@ -559,11 +559,11 @@ WRITE64_MEMBER(dc_state::dc_g2_ctrl_w )
 			old = m_wave_dma.start & 1;
 			m_wave_dma.start = dat & 1;
 
-			//#if DEBUG_AICA_DMA
+			#if DEBUG_AICA_DMA
 			printf("AICA: G2-DMA start \n");
 			printf("DST %08x SRC %08x SIZE %08x IND %02x\n",m_wave_dma.aica_addr,m_wave_dma.root_addr,m_wave_dma.size,m_wave_dma.indirect);
 			printf("SEL %08x ST  %08x FLAG %08x DIR %02x\n",m_wave_dma.sel,m_wave_dma.start,m_wave_dma.flag,m_wave_dma.dir);
-			//#endif
+			#endif
 
 			//mame_printf_verbose("SB_ADST data %08x\n",dat);
 			if(((old & 1) == 0) && m_wave_dma.flag && m_wave_dma.start && ((m_wave_dma.sel & 2) == 0)) // 0 -> 1

src/mess/drivers/dccons.c

@@ -26,8 +26,10 @@
 	- Sega GT: no cursor on main menu;
 	- Tetris 4D: hangs at BPS FMV (bp 0C0B0C4E)
 
-	Note:
+	Notes:
 	- DC US and DC PAL flash ROMs are definitely hacked, they are set to have Chinese instead of Japanese.
+	- 0x1a002 of flash ROM returns the region type (0x30=Japan, 0x31=USA, 0x32=Europe). Amusingly, if the value
+	  on a non-jp console is different than these ones, the system shows a black swirl (and nothing boots).
 	- gdi file for DCLP (a Dreamcast tester) doesn't have first two tracks info, they are:
 	  1 0 4 2048 FILE0001.DUP 0
       2 1798 0 2352 FILE0002.DUP 0