From 057474989c1a92e9e935dbc8cb9d233ba3a4ea3a Mon Sep 17 00:00:00 2001 From: jbu Date: Sat, 6 Aug 2016 04:34:23 +0200 Subject: [PATCH] alto2: remove more cruft and fix comments I want this child to become a grown up some day. --- src/devices/cpu/alto2/a2dht.cpp | 46 +++++++++++++++ src/devices/cpu/alto2/a2disk.cpp | 29 ---------- src/devices/cpu/alto2/a2disk.h | 8 --- src/devices/cpu/alto2/a2disp.cpp | 34 ++++++------ src/devices/cpu/alto2/a2disp.h | 89 ++++++++++++++++++------------ src/devices/cpu/alto2/a2dvt.cpp | 23 ++++++++ src/devices/cpu/alto2/a2dvt.h | 19 +++++-- src/devices/cpu/alto2/a2dwt.cpp | 31 +++++++++++ src/devices/cpu/alto2/a2mem.h | 6 +- src/devices/cpu/alto2/alto2cpu.cpp | 40 +++++++------- src/devices/cpu/alto2/alto2cpu.h | 5 +- src/devices/cpu/alto2/alto2dsm.cpp | 61 ++++++++++---------- 12 files changed, 237 insertions(+), 154 deletions(-) diff --git a/src/devices/cpu/alto2/a2dht.cpp b/src/devices/cpu/alto2/a2dht.cpp index 2f9aef63906..cf32394a83c 100644 --- a/src/devices/cpu/alto2/a2dht.cpp +++ b/src/devices/cpu/alto2/a2dht.cpp @@ -7,6 +7,52 @@ *****************************************************************************/ #include "alto2cpu.h" +/* + * Copied from ALTOCODE24.MU + * ;Display Horizontal Task. + * ;11 cycles if no block change, 17 if new control block. + * + * DHT: MAR← CBA-1; + * L← SLC -1, BUS=0; + * SLC← L, :DHT0; + * + * DHT0: T← 37400; MORE TO DO IN THIS BLOCK + * SINK← MD; + * L← T← MD AND T, SETMODE; + * HTAB← L LCY 8, :NORMODE; + * + * NORMODE:L← T← 377 . T; + * AECL← L, :REST; + * + * HALFMODE: L← T← 377 . T; + * AECL← L, :REST, T← 0; + * + * REST: L← DWA + T,TASK; INCREMENT DWA BY 0 OR NWRDS + * NDNX: DWA← L, :DHT; + * + * DHT1: L← T← MD+1, BUS=0; + * CBA← L, MAR← T, :MOREB; + * + * NOMORE: BLOCK, :DNX; + * MOREB: T← 37400; + * L← T← MD AND T, SETMODE; + * MAR← CBA+1, :NORMX, EVENFIELD; + * + * NORMX: HTAB← L LCY 8, :NODD; + * HALFX: HTAB← L LCY 8, :NEVEN; + * + * NODD: L←T← 377 . T; + * AECL← L, :XREST; ODD FIELD, FULL RESOLUTION + * + * NEVEN: L← 377 AND T; EVEN FIELD OR HALF RESOLUTION + * AECL←L, T←0; + * + * XREST: L← MD+T; + * T←MD-1; + * DNX: DWA←L, L←T, TASK; + * SLC←L, :DHT; + */ + /** * @brief f1_dht_block early: disable the display word task */ diff --git a/src/devices/cpu/alto2/a2disk.cpp b/src/devices/cpu/alto2/a2disk.cpp index c5088872e15..c4658726492 100644 --- a/src/devices/cpu/alto2/a2disk.cpp +++ b/src/devices/cpu/alto2/a2disk.cpp @@ -1620,14 +1620,6 @@ void alto2_cpu_device::disk_bitclk(void* ptr, INT32 arg) kwd_timing(clk, bit, 0); } -#if USE_BITCLK_TIMER - /* more bits to clock? */ - if (++arg < dhd->bits_per_sector()) { - m_dsk.bitclk_timer->adjust(dhd->bit_time(), arg); - } else { - m_dsk.bitclk_timer->reset(); - } -#else if (++arg < dhd->bits_per_sector()) { m_bitclk_time += m_dsk.bitclk_time[m_dsk.drive]; m_bitclk_index = arg; @@ -1635,7 +1627,6 @@ void alto2_cpu_device::disk_bitclk(void* ptr, INT32 arg) // stop the bitclock timer m_bitclk_time = -1; } -#endif } /** @@ -1649,16 +1640,11 @@ void alto2_cpu_device::next_sector(int unit) LOG((this,LOG_DISK,0,"%s dhd=%p\n", __FUNCTION__, dhd)); // get bit time in pico seconds m_dsk.bitclk_time[unit] = static_cast(dhd->bit_time().as_attoseconds() / 1000000); -#if USE_BITCLK_TIMER - LOG((this,LOG_DISK,0," unit #%d stop bitclk\n", unit)); - m_dsk.bitclk_timer->enable(false); -#else if (m_bitclk_time >= 0) { LOG((this,LOG_DISK,0," unit #%d stop bitclk\n", unit)); m_bitclk_time = -1; m_bitclk_index = -1; } -#endif /* KSTAT[0-3] update the current sector in the kstat field */ PUT_KSTAT_SECTOR(m_dsk.kstat, dhd->get_sector()); @@ -1669,12 +1655,6 @@ void alto2_cpu_device::next_sector(int unit) LOG((this,LOG_DISK,1," unit #%d sector %d start\n", unit, GET_KSTAT_SECTOR(m_dsk.kstat))); -#if USE_BITCLK_TIMER - // HACK: no command, no bit clock - if (debug_read_mem(0521)) - /* start a timer chain for the bit clock */ - disk_bitclk(0, 0); -#else // TODO: verify current sector == requested sector and only then run the bitclk? // HACK: no command, no bit clock if (debug_read_mem(0521)) @@ -1683,7 +1663,6 @@ void alto2_cpu_device::next_sector(int unit) m_bitclk_time = 0; m_bitclk_index = 0; } -#endif } /** @@ -1769,10 +1748,6 @@ void alto2_cpu_device::init_disk() m_dsk.kcom = 066000; -#if USE_BITCLK_TIMER - m_dsk.bitclk_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(alto2_cpu_device::disk_bitclk),this)); -#endif - m_dsk.strobon_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(alto2_cpu_device::disk_strobon),this)); m_dsk.strobon_timer->reset(); @@ -1821,12 +1796,8 @@ void alto2_cpu_device::reset_disk() m_dsk.strobe = 0; m_dsk.strobon_timer->reset(); m_dsk.bitclk = 0; -#if USE_BITCLK_TIMER - m_dsk.bitclk_timer->reset(); -#else m_dsk.bitclk_time[0] = static_cast(attotime::from_nsec(300).as_attoseconds() / 1000000); m_dsk.bitclk_time[1] = static_cast(attotime::from_nsec(300).as_attoseconds() / 1000000); -#endif m_dsk.datin = 0; m_dsk.bitcount = 0; m_dsk.seclate = 0; diff --git a/src/devices/cpu/alto2/a2disk.h b/src/devices/cpu/alto2/a2disk.h index 5fd994f654e..a3f8c7755fc 100644 --- a/src/devices/cpu/alto2/a2disk.h +++ b/src/devices/cpu/alto2/a2disk.h @@ -37,11 +37,7 @@ struct { UINT8 strobe; //!< strobe (still) active emu_timer* strobon_timer; //!< set strobe on timer UINT8 bitclk; //!< current bitclk state (either crystal clock, or rdclk from the drive) -#if USE_BITCLK_TIMER - emu_timer* bitclk_timer; //!< bit clock timer -#else int bitclk_time[2]; //!< per drive time in clocks per bit -#endif UINT8 datin; //!< current datin from the drive UINT8 bitcount; //!< bit counter UINT8 carry; //!< carry output of the bitcounter @@ -78,11 +74,7 @@ TIMER_CALLBACK_MEMBER( disk_seclate ); //!< timer callback to take away TIMER_CALLBACK_MEMBER( disk_ok_to_run ); //!< timer callback to take away the OK TO RUN pulse (reset) TIMER_CALLBACK_MEMBER( disk_strobon ); //!< timer callback to pulse the STROBE' signal to the drive TIMER_CALLBACK_MEMBER( disk_ready_mf31a ); //!< timer callback to change the READY monoflop 31a -#if USE_BITCLK_TIMER -TIMER_CALLBACK_MEMBER( disk_bitclk ); //!< callback to update the disk controller with a new bitclk -#else void disk_bitclk(void *ptr, int arg); //!< function to update the disk controller with a new bitclk -#endif void disk_block(int task); //!< called if one of the disk tasks (task_kwd or task_ksec) blocks void bs_early_read_kstat(); //!< bus source: bus driven by disk status register KSTAT void bs_early_read_kdata(); //!< bus source: bus driven by disk data register KDATA input diff --git a/src/devices/cpu/alto2/a2disp.cpp b/src/devices/cpu/alto2/a2disp.cpp index 825699f69af..e7a0474ea7c 100644 --- a/src/devices/cpu/alto2/a2disp.cpp +++ b/src/devices/cpu/alto2/a2disp.cpp @@ -10,10 +10,10 @@ /** * @brief PROM a38 contains the STOPWAKE' and MBEMBPTY' signals for the FIFO - * 
  * The inputs to a38 are the UNLOAD counter RA[0-3] and the DDR<- counter
  * WA[0-3], and the designer decided to reverse the address lines :-)
  *
+ * 
  *  a38  counter
  *  -------------
  *   A0  RA[0]
@@ -50,10 +50,10 @@ static const prom_load_t pl_displ_a38 =
 };
 
 //! PROM a38 bit O1 is STOPWAKE' (stop DWT if bit is zero)
-#define FIFO_STOPWAKE(a38) (0 == (a38 & disp_a38_STOPWAKE) ? true : false)
+#define FIFO_STOPWAKE(a38) ((a38 & disp_a38_STOPWAKE) ? false : true)
 
 //! PROM a38 bit O3 is MBEMPTY' (FIFO is empty if bit is zero)
-#define FIFO_MBEMPTY(a38) (0 == (a38 & disp_a38_MBEMPTY) ? true : false)
+#define FIFO_MBEMPTY(a38) ((a38 & disp_a38_MBEMPTY) ? false : true)
 
 /**
  * @brief emulation of PROM a63 in the display schematics page 8
@@ -224,17 +224,17 @@ static const UINT16 double_bits[256] = {
 	0xffc0,0xffc3,0xffcc,0xffcf,0xfff0,0xfff3,0xfffc,0xffff
 };
 
-#define HLC1    ((m_dsp.hlc >>  0) & 1)     //!< horizontal line counter bit 0 (mid of the scanline)
-#define HLC2    ((m_dsp.hlc >>  1) & 1)     //!< horizontal line counter bit 1
-#define HLC4    ((m_dsp.hlc >>  2) & 1)     //!< horizontal line counter bit 2
-#define HLC8    ((m_dsp.hlc >>  3) & 1)     //!< horizontal line counter bit 3
-#define HLC16   ((m_dsp.hlc >>  4) & 1)     //!< horizontal line counter bit 4
-#define HLC32   ((m_dsp.hlc >>  5) & 1)     //!< horizontal line counter bit 5
-#define HLC64   ((m_dsp.hlc >>  6) & 1)     //!< horizontal line counter bit 6
-#define HLC128  ((m_dsp.hlc >>  7) & 1)     //!< horizontal line counter bit 7
-#define HLC256  ((m_dsp.hlc >>  8) & 1)     //!< horizontal line counter bit 8
-#define HLC512  ((m_dsp.hlc >>  9) & 1)     //!< horizontal line counter bit 9
-#define HLC1024 ((m_dsp.hlc >> 10) & 1)     //!< horizontal line counter bit 10 (odd/even field)
+#define HLC1    X_BIT(m_dsp.hlc,16,15)    //!< horizontal line counter bit 0 (mid of the scanline)
+#define HLC2    X_BIT(m_dsp.hlc,16,14)    //!< horizontal line counter bit 1
+#define HLC4    X_BIT(m_dsp.hlc,16,13)    //!< horizontal line counter bit 2
+#define HLC8    X_BIT(m_dsp.hlc,16,12)    //!< horizontal line counter bit 3
+#define HLC16   X_BIT(m_dsp.hlc,16,11)    //!< horizontal line counter bit 4
+#define HLC32   X_BIT(m_dsp.hlc,16,10)    //!< horizontal line counter bit 5
+#define HLC64   X_BIT(m_dsp.hlc,16, 9)    //!< horizontal line counter bit 6
+#define HLC128  X_BIT(m_dsp.hlc,16, 8)    //!< horizontal line counter bit 7
+#define HLC256  X_BIT(m_dsp.hlc,16, 7)    //!< horizontal line counter bit 8
+#define HLC512  X_BIT(m_dsp.hlc,16, 6)    //!< horizontal line counter bit 9
+#define HLC1024 X_BIT(m_dsp.hlc,16, 5)    //!< horizontal line counter bit 10 (odd/even field
 
 #define GET_SETMODE_SPEEDY(mode) X_RDBITS(mode,16,0,0)  //!< get the pixel clock speed from a SETMODE<- bus value
 #define GET_SETMODE_INVERSE(mode) X_RDBITS(mode,16,1,1) //!< get the inverse video flag from a SETMODE<- bus value
@@ -287,12 +287,12 @@ void alto2_cpu_device::unload_word()
 
 	if (m_dsp.halfclock)
 	{
-		UINT16 word1 = double_bits[word / 256];
-		UINT16 word2 = double_bits[word % 256];
+		const UINT16 word1 = double_bits[word / 256];
 		update_framebuf_word(framebuf, x, y, word1);
 		x++;
 		if (x < ALTO2_DISPLAY_VISIBLE_WORDS)
 		{
+			const UINT16 word2 = double_bits[word % 256];
 			update_framebuf_word(framebuf, x, y, word2);
 			x++;
 		}
@@ -329,7 +329,7 @@ void alto2_cpu_device::display_state_machine()
 	{
 		// count horizontal line counters and wrap
 		m_dsp.hlc += 1;
-		if (m_dsp.hlc == ALTO2_DISPLAY_HLC_END)
+		if (m_dsp.hlc > ALTO2_DISPLAY_HLC_END)
 			m_dsp.hlc = ALTO2_DISPLAY_HLC_START;
 		// wake up the memory refresh task _twice_ on each scanline
 		m_task_wakeup |= 1 << task_mrt;
diff --git a/src/devices/cpu/alto2/a2disp.h b/src/devices/cpu/alto2/a2disp.h
index fed97913d46..282ccd94f56 100644
--- a/src/devices/cpu/alto2/a2disp.h
+++ b/src/devices/cpu/alto2/a2disp.h
@@ -2,13 +2,13 @@
 // copyright-holders:Juergen Buchmueller
 /*****************************************************************************
  *
- *   Xerox AltoII display block
+ *   Xerox AltoII display emulation
  *
  *****************************************************************************/
 #ifdef  ALTO2_DEFINE_CONSTANTS
 
 /**
- * @brief start value for the horizontal line counter
+ * @brief Start value for the horizontal line counter.
  *
  * This value is loaded into the three 4 bit counters (type 9316)
  * with numbers 65, 67, and 75.
@@ -21,12 +21,14 @@
 #define ALTO2_DISPLAY_HLC_START (2+4+16+128)
 
 /**
- * @brief end value for the horizontal line counter
+ * @brief End value for the horizontal line counter.
  *
  * This is decoded by H30, an 8 input NAND gate.
  * The value is 1899; horz. line count range 150...1899 = 1750.
+ * So there are 1750 / 2 = 875 total scanlines.
  *
- * There are 1750 / 2 = 875 total scanlines.
+ * Note: The horizontal line counts 150 ... 1023 for the even field,
+ * and 1024 ... 1899 for the odd field.
  */
 #define ALTO2_DISPLAY_HLC_END (1+2+8+32+64+256+512+1024)
 
@@ -37,7 +39,7 @@
  * scanlines to the monitor. The frame rate is 60Hz, which is actually the rate
  * of the half-frames. The rate for full frames is thus 30Hz.
  */
-#define ALTO2_DISPLAY_TOTAL_HEIGHT ((ALTO2_DISPLAY_HLC_END + 1 - ALTO2_DISPLAY_HLC_START) / 2)
+#define ALTO2_DISPLAY_TOTAL_HEIGHT ((ALTO2_DISPLAY_HLC_END - ALTO2_DISPLAY_HLC_START) / 2)
 
 /**
  * @brief display total width, including horizontal blanking
@@ -68,18 +70,37 @@
  */
 #define ALTO2_DISPLAY_TOTAL_WIDTH 768
 
+//! The display fifo has 16 words.
+#define ALTO2_DISPLAY_FIFO 16
 
-#define ALTO2_DISPLAY_FIFO 16                                                       //!< the display fifo has 16 words
-#define ALTO2_DISPLAY_SCANLINE_WORDS (ALTO2_DISPLAY_TOTAL_WIDTH/16)                 //!< words per scanline
-#define ALTO2_DISPLAY_HEIGHT 808                                                    //!< number of visible scanlines per frame; 808 really, but there are some empty lines?
-#define ALTO2_DISPLAY_WIDTH 606                                                     //!< visible width of the display; 38 x 16 bit words - 2 pixels
-#define ALTO2_DISPLAY_VISIBLE_WORDS ((ALTO2_DISPLAY_WIDTH+15)/16)                   //!< visible words per scanline
-#define ALTO2_DISPLAY_BITCLOCK 20160000ll                                           //!< display bit clock in Hertz (20.16MHz)
-#define ALTO2_DISPLAY_BITTIME(n) (U64(1000000000000)*(n)/ALTO2_DISPLAY_BITCLOCK)    //!< display bit time in pico seconds (~= 49.6031ns)
-#define ALTO2_DISPLAY_SCANLINE_TIME ALTO2_DISPLAY_BITTIME(ALTO2_DISPLAY_TOTAL_WIDTH)//!< time for a scanline in pico seconds (768 * 49.6031ns ~= 38095.1808ns)
-#define ALTO2_DISPLAY_VISIBLE_TIME ALTO2_DISPLAY_BITTIME(ALTO2_DISPLAY_WIDTH)       //!< time of the visible part of a scanline in pico seconds (606 * 49.6031ns ~= 30059.4786ns)
-#define ALTO2_DISPLAY_WORD_TIME ALTO2_DISPLAY_BITTIME(16)                           //!< time for a word in pico seconds (16 pixels * 49.6031ns ~= 793.6496ns)
-#define ALTO2_DISPLAY_VBLANK_TIME ((ALTO2_DISPLAY_TOTAL_HEIGHT-ALTO2_DISPLAY_HEIGHT)*HZ_TO_ATTOSECONDS(26250)/2)
+//! Words per scanline.
+#define ALTO2_DISPLAY_SCANLINE_WORDS (ALTO2_DISPLAY_TOTAL_WIDTH/16)
+
+//! Number of visible scanlines per frame; 808 really, but there are some empty lines?
+#define ALTO2_DISPLAY_HEIGHT 808
+
+//! Visible width of the display; 38 x 16 bit words - 2 pixels.
+#define ALTO2_DISPLAY_WIDTH 606
+
+//! Visible words per scanline.
+#define ALTO2_DISPLAY_VISIBLE_WORDS ((ALTO2_DISPLAY_WIDTH+15)/16)
+
+//! Display bit clock in Hertz (20.16MHz).
+#define ALTO2_DISPLAY_BITCLOCK 20160000ll
+
+//! Display bit time in pico seconds (~= 49.6031ns).
+#define ALTO2_DISPLAY_BITTIME(n) (U64(1000000000000)*(n)/ALTO2_DISPLAY_BITCLOCK)
+
+//! Time for a scanline in pico seconds (768 * 49.6031ns ~= 38095.1808ns).
+#define ALTO2_DISPLAY_SCANLINE_TIME ALTO2_DISPLAY_BITTIME(ALTO2_DISPLAY_TOTAL_WIDTH)
+
+//!< Time of the visible part of a scanline in pico seconds (606 * 49.6031ns ~= 30059.4786ns).
+#define ALTO2_DISPLAY_VISIBLE_TIME ALTO2_DISPLAY_BITTIME(ALTO2_DISPLAY_WIDTH)
+
+//!< Time for a word in pico seconds (16 pixels * 49.6031ns ~= 793.6496ns).
+#define ALTO2_DISPLAY_WORD_TIME ALTO2_DISPLAY_BITTIME(16)
+
+#define ALTO2_DISPLAY_VBLANK_TIME ((ALTO2_DISPLAY_TOTAL_HEIGHT-ALTO2_DISPLAY_HEIGHT)*HZ_TO_ATTOSECONDS(26250))
 
 #else   // ALTO2_DEFINE_CONSTANTS
 /**
@@ -172,26 +193,26 @@
 #ifndef _A2DISP_H_
 #define _A2DISP_H_
 struct {
-	UINT16 state;                           //!< current state of the display_state_machine()
-	UINT16 hlc;                             //!< horizontal line counter
-	UINT16 setmode;                         //!< value written by last SETMODE<-
-	UINT16 inverse;                         //!< set to 0xffff if line is inverse, 0x0000 otherwise
-	bool halfclock;                         //!< set 0 for normal pixel clock, 1 for half pixel clock
+	UINT32 state;                           //!< current state of the display_state_machine()
+	UINT32 hlc;                             //!< horizontal line counter
+	UINT32 setmode;                         //!< value written by last SETMODE<-
+	UINT32 inverse;                         //!< set to 0xffff if line is inverse, 0x0000 otherwise
+	bool halfclock;                         //!< false for normal pixel clock, true for half pixel clock
 	UINT16 fifo[ALTO2_DISPLAY_FIFO];        //!< display word fifo
-	UINT8 wa;                               //!< fifo input pointer (write address; 4-bit)
-	UINT8 ra;                               //!< fifo output pointer (read address; 4-bit)
-	UINT8 a63;                              //!< most recent value read from the PROM a63
-	UINT8 a66;                              //!< most recent value read from the PROM a66
-	bool dht_blocks;                        //!< set non-zero, if the DHT executed BLOCK
-	bool dwt_blocks;                        //!< set non-zero, if the DWT executed BLOCK
-	bool curt_blocks;                       //!< set non-zero, if the CURT executed BLOCK
-	bool curt_wakeup;                       //!< set non-zero, if CURT wakeups are generated
-	UINT16 vblank;                          //!< most recent HLC with VBLANK still high (11-bit)
-	UINT16 xpreg;                           //!< cursor cursor x position register (10-bit)
-	UINT16 csr;                             //!< cursor shift register (16-bit)
+	UINT32 wa;                              //!< fifo input pointer (write address; 4-bit)
+	UINT32 ra;                              //!< fifo output pointer (read address; 4-bit)
+	UINT32 a63;                             //!< most recent value read from the PROM a63
+	UINT32 a66;                             //!< most recent value read from the PROM a66
+	bool dht_blocks;                        //!< set true, if the DHT executed BLOCK
+	bool dwt_blocks;                        //!< set true, if the DWT executed BLOCK
+	bool curt_blocks;                       //!< set true, if the CURT executed BLOCK
+	bool curt_wakeup;                       //!< set true, if CURT wakeups are generated
+	UINT32 vblank;                          //!< most recent HLC with VBLANK still high (11-bit)
+	UINT32 xpreg;                           //!< cursor cursor x position register (10-bit)
+	UINT32 csr;                             //!< cursor shift register (16-bit)
 	UINT32 curxpos;                         //!< helper: first cursor word in scanline
-	UINT16 cursor0;                         //!< helper: shifted cursor data for left word
-	UINT16 cursor1;                         //!< helper: shifted cursor data for right word
+	UINT32 cursor0;                         //!< helper: shifted cursor data for left word
+	UINT32 cursor1;                         //!< helper: shifted cursor data for right word
 	std::unique_ptr framebuf;     //!< array of words of the raw bitmap that is displayed
 	UINT8 *patterns;                        //!< array of 65536 patterns (16 bytes) with 1 byte per pixel
 	std::unique_ptr bitmap;   //!< MAME bitmap with 16 bit indices
diff --git a/src/devices/cpu/alto2/a2dvt.cpp b/src/devices/cpu/alto2/a2dvt.cpp
index ad019b6b07b..2badc246b57 100644
--- a/src/devices/cpu/alto2/a2dvt.cpp
+++ b/src/devices/cpu/alto2/a2dvt.cpp
@@ -7,6 +7,29 @@
  *****************************************************************************/
 #include "alto2cpu.h"
 
+/*
+ * Copied from ALTOCODE24.MU
+ *
+ *	;Display Vertical Task
+ *
+ *	DVT:	MAR← L← DASTART+1;
+ *		CBA← L, L← 0;
+ *		CURDATA← L;
+ *		SLC← L;
+ *		T← MD;			CAUSE A VERTICAL FIELD INTERRUPT
+ *		L← NWW OR T;
+ *		MAR← CURLOC;		SET UP THE CURSOR
+ *		NWW← L, T← 0-1;
+ *		L← MD XOR T;		HARDWARE EXPECTS X COMPLEMENTED
+ *		T← MD, EVENFIELD;
+ *		CURX← L, :DVT1;
+ *
+ *	DVT1:	L← BIAS-T-1, TASK, :DVT2;	BIAS THE Y COORDINATE 
+ *	DVT11:	L← BIAS-T, TASK;
+ * 
+ *	DVT2:	YPOS← L, :DVT;
+ */
+
 /**
  * @brief f1_dvt_block early: disable the display word task
  */
diff --git a/src/devices/cpu/alto2/a2dvt.h b/src/devices/cpu/alto2/a2dvt.h
index 3b73ac7bf7e..0d9430b1731 100644
--- a/src/devices/cpu/alto2/a2dvt.h
+++ b/src/devices/cpu/alto2/a2dvt.h
@@ -16,10 +16,19 @@ enum {
 	f2_dvt_evenfield    = f2_task_10            //!< f2 10: load even field
 };
 
-void f1_early_dvt_block();                      //!< F1 func: disable the display word task
-void activate_dvt();                            //!< called by the CPU when the display vertical task becomes active
-void init_dvt(int task = task_dvt);             //!< initialize the display vertical task
-void exit_dvt();                                //!< deinitialize the display vertical task
-void reset_dvt();                               //!< reset the display vertical task
+//! F1 func: Disable the display word task.
+void f1_early_dvt_block();
+
+//! Called by the CPU when the display vertical task becomes active.
+void activate_dvt();
+
+//! Initialize the display vertical task.
+void init_dvt(int task = task_dvt);
+
+//! Deinitialize the display vertical task.
+void exit_dvt();
+
+//! Reset the display vertical task.
+void reset_dvt();
 #endif  // _A2DVT_H_
 #endif  // ALTO2_DEFINE_CONSTANTS
diff --git a/src/devices/cpu/alto2/a2dwt.cpp b/src/devices/cpu/alto2/a2dwt.cpp
index 3c6867b9f05..6791c8cc6ff 100644
--- a/src/devices/cpu/alto2/a2dwt.cpp
+++ b/src/devices/cpu/alto2/a2dwt.cpp
@@ -7,6 +7,37 @@
  *****************************************************************************/
 #include "alto2cpu.h"
 
+/*
+ * Copied from ALTOCODE24.MU
+ *
+ *	;Display Word Task
+ *	
+ *	DWT:	T← DWA;
+ *		T←-3+T+1;
+ *		L← AECL+T,BUS=0,TASK;	AECL CONTAINS NWRDS AT THIS TIME
+ *		AECL←L, :DWTZ;
+ *	
+ *	DWTY:	BLOCK;
+ *		TASK, :DWTF;
+ *	
+ *	DWTZ:	L←HTAB-1, BUS=0,TASK;
+ *		HTAB←L, :DOTAB;
+ *
+ *	DOTAB:	DDR←0, :DWTZ;
+ *	NOTAB:	MAR←T←DWA;
+ *		L←AECL-T-1;
+ *		ALUCY, L←2+T;
+ *		DWA←L, :XNOMORE;
+ *
+ *	DOMORE:	DDR←MD, TASK;
+ *		DDR←MD, :NOTAB;
+ *
+ *	XNOMORE:DDR← MD, BLOCK;
+ *		DDR← MD, TASK;
+ *
+ *	DWTF:	:DWT;
+ */
+
 //! PROM a38 bit O1 is STOPWAKE' (stop DWT if bit is zero)
 #define FIFO_STOPWAKE(a38) (0 == (a38 & disp_a38_STOPWAKE) ? true : false)
 
diff --git a/src/devices/cpu/alto2/a2mem.h b/src/devices/cpu/alto2/a2mem.h
index 3985c065060..0f00d16fbeb 100644
--- a/src/devices/cpu/alto2/a2mem.h
+++ b/src/devices/cpu/alto2/a2mem.h
@@ -31,7 +31,7 @@ struct {
 	UINT32 mar;                         //!< memory address register
 	UINT32 rmdd;                        //!< read memory data double-word
 	UINT32 wmdd;                        //!< write memory data double-word
-	UINT16 md;                          //!< memory data register
+	UINT32 md;                          //!< memory data register
 	UINT64 cycle;                       //!< cycle when the memory address register was loaded
 
 	/**
@@ -44,8 +44,8 @@ struct {
 	int access;
 	bool error;                         //!< non-zero after a memory error was detected
 	UINT32 mear;                        //!< memory error address register
-	UINT16 mesr;                        //!< memory error status register
-	UINT16 mecr;                        //!< memory error control register
+	UINT32 mesr;                        //!< memory error status register
+	UINT32 mecr;                        //!< memory error control register
 }   m_mem;
 
 /**
diff --git a/src/devices/cpu/alto2/alto2cpu.cpp b/src/devices/cpu/alto2/alto2cpu.cpp
index bd447e09583..dc82e9721c1 100644
--- a/src/devices/cpu/alto2/alto2cpu.cpp
+++ b/src/devices/cpu/alto2/alto2cpu.cpp
@@ -876,10 +876,8 @@ void alto2_cpu_device::device_start()
 	save_item(NAME(m_dsp_time));
 	save_item(NAME(m_unload_time));
 	save_item(NAME(m_unload_word));
-#if (USE_BITCLK_TIMER == 0)
 	save_item(NAME(m_bitclk_time));
 	save_item(NAME(m_bitclk_index));
-#endif
 	save_item(NAME(m_mouse.x));
 	save_item(NAME(m_mouse.y));
 	save_item(NAME(m_mouse.dx));
@@ -1458,6 +1456,8 @@ void alto2_cpu_device::bs_late_load_r()
 {
 	if (f2() != f2_emu_load_dns) {
 		m_r[m_rsel] = m_shifter;
+		if (m_rsel == 037)
+			m_r[m_rsel] &= ~3;
 		LOG((this,LOG_CPU,2,"    R%02o<-; %s = SHIFTER (%#o)\n", m_rsel, r_name(m_rsel), m_shifter));
 	}
 }
@@ -2279,8 +2279,6 @@ void alto2_cpu_device::execute_run()
 	m_next2 = m_task_next2[m_task];
 
 	do {
-		int do_bs, flags;
-
 		m_mpc = m_next;             // next instruction's micro program counter
 		m_mir = RD_UCODE(m_mpc);    // fetch the micro code
 
@@ -2303,13 +2301,15 @@ void alto2_cpu_device::execute_run()
 		 * or f2 == f2_const. These functions use the MIR BS field to
 		 * provide a part of the address to the constant ROM instead.
 		 */
-		do_bs = !(f1() == f1_const || f2() == f2_const);
+		bool do_bs = f1() != f1_const && f2() != f2_const;
 		if (do_bs && bs() == bs_read_md && check_mem_read_stall()) {
 			LOG((this,LOG_CPU,3, "   <-MD stall\n"));
 			continue;
 		}
+
 		// now read the next instruction field from the MIR and modify it
 		m_next = next() | m_next2;
+
 		// prefetch the next instruction's next field as next2
 		m_next2 = X_RDBITS(RD_UCODE(m_next), 32, NEXT0, NEXT9) | (m_next2 & ~ALTO2_UCODE_PAGE_MASK);
 		LOG((this,LOG_CPU,2,"%s-%04o: %011o r:%02o aluf:%02o bs:%02o f1:%02o f2:%02o t:%o l:%o next:%05o next2:%05o\n",
@@ -2323,9 +2323,9 @@ void alto2_cpu_device::execute_run()
 
 		// The constant memory is gated to the bus by F1 == f1_const, F2 == f2_const, or BS >= 4
 		if (!do_bs || bs() >= bs_task_4) {
-			UINT32 addr = 8 * m_rsel + bs();
+			const UINT32 addr = 8 * m_rsel + bs();
 			// FIXME: is the format of m_const_data endian safe?
-			UINT16 data = m_const_data[2*addr] | (m_const_data[2*addr+1] << 8);
+			const UINT16 data = m_const_data[2*addr] | (m_const_data[2*addr+1] << 8);
 			m_bus &= data;
 			LOG((this,LOG_CPU,2,"    %#o; BUS &= %#o CONST[%03o]\n", m_bus, data, addr));
 		}
@@ -2353,10 +2353,10 @@ void alto2_cpu_device::execute_run()
 		 *
 		 * B1 and B3-B7 are inverted on loading the PROM
 		 */
-		UINT8 a10 = m_alu_a10[(m_emu.skip << 4) | aluf()];
-		UINT32 alu = alu_74181(m_bus, m_t, a10);
+		const UINT8 a10 = m_alu_a10[(m_emu.skip << 4) | aluf()];
+		const UINT32 alu = alu_74181(m_bus, m_t, a10);
+		const int flags = a10 & (TSELECT | ALUM);
 		m_aluc0 = (alu >> 16) & 1;
-		flags = a10 & (TSELECT | ALUM);
 		m_alu = static_cast(alu);
 
 		// WRTRAM must happen now before L is changed
@@ -2426,17 +2426,18 @@ void alto2_cpu_device::execute_run()
 			}
 		}
 
-		/**
-		 * Subtract the microcycle time from the display time accu.
-		 * If it underflows, call the display state machine and add
-		 * the time for 32(!) pixel clocks to the accu.
-		 * This is very close to every seventh CPU cycle (really?)
-		 */
 		if (m_dsp_time >= 0) {
+			/**
+			 * Subtract the microcycle time from the display time accu.
+			 * If it underflows, call the display state machine and add
+			 * the time for 32(!) pixel clocks to the accu.
+			 * This is very close to every seventh CPU cycle
+			 */
 			m_dsp_time -= ALTO2_UCYCLE;
 			if (m_dsp_time < 0)
 				display_state_machine();
 		}
+
 		if (m_unload_time >= 0) {
 			/**
 			 * Subtract the microcycle time from the unload time accu.
@@ -2448,9 +2449,9 @@ void alto2_cpu_device::execute_run()
 			if (m_unload_time < 0)
 				unload_word();
 		}
-#if (USE_BITCLK_TIMER == 0)
+		
 		if (m_bitclk_time >= 0) {
-			/*
+			/**
 			 * Subtract the microcycle time from the bitclk time accu.
 			 * If it underflows, call the disk bitclk function which adds
 			 * the time for one bit as clocks to the accu, or ends
@@ -2459,7 +2460,6 @@ void alto2_cpu_device::execute_run()
 			m_bitclk_time -= ALTO2_UCYCLE;
 			disk_bitclk(nullptr, m_bitclk_index);
 		}
-#endif
 	} while (m_icount-- > 0);
 
 	/* save this task's mpc and address modifier */
@@ -2566,7 +2566,5 @@ void alto2_cpu_device::soft_reset()
 
 	m_dsp_time = 0;                 // reset the display state machine timing accu
 	m_unload_time = 0;              // reset the word unload timing accu
-#if (USE_BITCLK_TIMER == 0)
 	m_bitclk_time = 0;              // reset the bitclk timing accu
-#endif
 }
diff --git a/src/devices/cpu/alto2/alto2cpu.h b/src/devices/cpu/alto2/alto2cpu.h
index 72567af3ae3..821286ae2fa 100644
--- a/src/devices/cpu/alto2/alto2cpu.h
+++ b/src/devices/cpu/alto2/alto2cpu.h
@@ -50,7 +50,6 @@ enum {
 #endif
 
 #define USE_PRIO_F9318          0           //!< define to 1 to use the F9318 priority encoder code (broken)
-#define USE_BITCLK_TIMER        0           //!< define to 1 to use a very high rate timer for the disk bit clock
 
 #define ALTO2_TASKS             16          //!< 16 task slots
 #define ALTO2_REGS              32          //!< 32 16-bit words in the R register file
@@ -592,10 +591,8 @@ private:
 	int m_dsp_time;                                 //!< display_state_machine() time accu
 	int m_unload_time;                              //!< unload word time accu
 	int m_unload_word;                              //!< unload word number
-#if (USE_BITCLK_TIMER == 0)
 	int m_bitclk_time;                              //!< bitclk call time accu
-	int m_bitclk_index;                             //!< bitclk index (bit number)
-#endif
+	int m_bitclk_index;                             //!< bitclk index (bit number in sector)
 
 	static const char *task_name(int task);         //!< human readable task names
 	static const char *r_name(UINT8 reg);           //!< human readable register names
diff --git a/src/devices/cpu/alto2/alto2dsm.cpp b/src/devices/cpu/alto2/alto2dsm.cpp
index 7139243d0ba..d899cb4f8b5 100644
--- a/src/devices/cpu/alto2/alto2dsm.cpp
+++ b/src/devices/cpu/alto2/alto2dsm.cpp
@@ -214,14 +214,14 @@ offs_t alto2_cpu_device::disasm_disassemble(char *buffer, offs_t pc, const UINT8
 			(static_cast(oprom[1]) << 16) |
 			(static_cast(oprom[2]) << 8) |
 			(static_cast(oprom[3]) << 0);
-	UINT8 rsel = static_cast((mir >> 27) & 31);
-	UINT8 aluf = static_cast((mir >> 23) & 15);
-	UINT8 bs = static_cast((mir >> 20) & 7);
-	UINT8 f1 = static_cast((mir >> 16) & 15);
-	UINT8 f2 = static_cast((mir >> 12) & 15);
-	UINT8 t = static_cast((mir >> 11) & 1);
-	UINT8 l = static_cast((mir >> 10) & 1);
-	offs_t next = static_cast(mir & 1023);
+	int rsel = (mir >> 27) & 31;
+	int aluf = (mir >> 23) & 15;
+	int bs = (mir >> 20) & 7;
+	int f1 = (mir >> 16) & 15;
+	int f2 = (mir >> 12) & 15;
+	int t = (mir >> 11) & 1;
+	int l = (mir >> 10) & 1;
+	offs_t next = mir & 1023;
 	const UINT8* src = oprom - 4 * pc + 4 * next;
 	UINT32 next2 =  (static_cast(src[0]) << 24) |
 			(static_cast(src[1]) << 16) |
@@ -244,52 +244,52 @@ offs_t alto2_cpu_device::disasm_disassemble(char *buffer, offs_t pc, const UINT8
 	switch (aluf) {
 	case  0: // T?: BUS
 		// this is somehow redundant and just wasting space
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS) ");
+		// dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS) ");
 		break;
 	case  1: //   : T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "T ");
 		break;
 	case  2: // T?: BUS OR T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS|T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS|T ");
 		break;
 	case  3: //   : BUS AND T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS&T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS&T ");
 		break;
 	case  4: //   : BUS XOR T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS^T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS^T ");
 		break;
 	case  5: // T?: BUS + 1
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS+1) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS+1 ");
 		break;
 	case  6: // T?: BUS - 1
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS-1) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS-1 ");
 		break;
 	case  7: //   : BUS + T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS+T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS+T ");
 		break;
 	case  8: //   : BUS - T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS-T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS-T ");
 		break;
 	case  9: //   : BUS - T - 1
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS-T-1) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS-T-1 ");
 		break;
 	case 10: // T?: BUS + T + 1
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS+T+1) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS+T+1 ");
 		break;
 	case 11: // T?: BUS + SKIP
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS+SKIP) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS+SKIP ");
 		break;
 	case 12: // T?: BUS, T (AND)
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS,T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS,T ");
 		break;
 	case 13: //   : BUS AND NOT T
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "ALUF(BUS&~T) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS&~T ");
 		break;
 	case 14: //   : undefined
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "*ALUF(BUS) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "*BUS ");
 		break;
 	case 15: //   : undefined
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "*ALUF(BUS) ");
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "*BUS ");
 		break;
 	}
 
@@ -344,7 +344,7 @@ offs_t alto2_cpu_device::disasm_disassemble(char *buffer, offs_t pc, const UINT8
 		break;
 	case 7: // put the constant from PROM (RSELECT,BS) on the bus
 		pa = (rsel << 3) | bs;
-		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS<-%05o CONST[%03o]", const_prom[pa], pa);
+		dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS<-%05o", const_prom[pa]);
 		break;
 	default:
 		dst += snprintf(dst, len - (size_t)(dst - buffer), "F1_%02o ", f1);
@@ -373,13 +373,13 @@ offs_t alto2_cpu_device::disasm_disassemble(char *buffer, offs_t pc, const UINT8
 		dst += snprintf(dst, len - (size_t)(dst - buffer), "[ALUC0 ? %s:%s] ",
 			addrname((prefetch | 1) & MCODE_MASK), addrname(prefetch & MCODE_MASK));
 		break;
-	case 6: // deliver BUS data to memory
+	case 6: // write BUS data to memory
 		dst += snprintf(dst, len - (size_t)(dst - buffer), "MD<-BUS ");
 		break;
-	case 7: // put on the bus the constant from PROM (RSELECT,BS)
+	case 7: // put the constant from PROM (RSELECT,BS) on the bus
 		if (f1 != 7) {
 			pa = 8 * rsel + bs;
-			dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS<-%05o CONST[%03o]", const_prom[pa], pa);
+			dst += snprintf(dst, len - (size_t)(dst - buffer), "BUS<-%05o", const_prom[pa]);
 		}
 		break;
 	default:
@@ -387,10 +387,5 @@ offs_t alto2_cpu_device::disasm_disassemble(char *buffer, offs_t pc, const UINT8
 		break;
 	}
 
-	// Simplify output based on text
-	// ALUF(BUS) is a no-op if followed by BUS<-
-	while (NULL != (dst = strstr(buffer, "ALUF(BUS) BUS<-")))
-		strcpy(dst, dst + 15);
-
 	return result;
 }