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Imlac: Model MSB and LSB accumulators.

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- Improve debug output.
- Add support for Alpha display processor.
   Details figured out by Zachary Harper @sparky-z from reading the
   listing "FREEWAY CROSSING PROGRAM".
This commit is contained in:
Lars Brinkhoff 2025-06-02 12:57:07 +02:00 committed by Mark Pizzolato
parent f9b39fb87f
commit 5b07ac973e
1 changed files with 38 additions and 13 deletions
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51
imlac/imlac_dp.c
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@ -72,8 +72,10 @@ static REG dp_reg[] = {
{ ORDATAD (MODE, MODE, 1, "Display mode") },
{ BRDATAD (DT, DT, 8, 16, 8, "Return address stack") },
{ ORDATAD (SP, SP, 3, "Stack pointer") },
{ ORDATAD (XMSB, XMSB, 11, "X accumulator") },
{ ORDATAD (YMSB, YMSB, 11, "Y accumulator") },
{ ORDATAD (XMSB, XMSB, 7, "X accumulator MSB") },
{ ORDATAD (XLSB, XLSB, 5, "X accumulator LSB") },
{ ORDATAD (YMSB, YMSB, 7, "Y accumulator MSB") },
{ ORDATAD (YLSB, YLSB, 5, "Y accumulator LSB") },
{ ORDATAD (SCALE, SCALE, 3, "Scale") },
{ ORDATAD (BLOCK, BLOCK, 3, "Block") },
{ ORDATAD (MIT8K, MIT8K, 1, "MIT 8K addressing") },
@ -84,7 +86,7 @@ static REG dp_reg[] = {
static MTAB dp_mod[] = {
{ DP_ALPHA, DP_ALPHA, "Alpha machine", "ALPHA",
NULL, NULL, NULL, "Enables Alpha display processor" },
{ DP_ALPHA, 0, "Graphics machine", "ALPHA",
{ DP_ALPHA, 0, "Graphics machine", "GRAPHICS",
NULL, NULL, NULL, "Disables Alpha display processor" },
{ 0 }
};
@ -189,6 +191,8 @@ static uint16 deflect (uint16 msb, uint16 lsb)
static void increment (uint16 *msb, uint16 *lsb, uint16 x)
{
/* On an Alpha machine, the LSB doesn't carry to the MSB. */
*lsb += SCALE * x;
if (dp_unit.flags & DP_ALPHA)
return;
@ -199,6 +203,8 @@ static void increment (uint16 *msb, uint16 *lsb, uint16 x)
static void decrement (uint16 *msb, uint16 *lsb, uint16 x)
{
/* On an Alpha machine, the LSB doesn't carry to the MSB. */
*lsb -= SCALE * x;
if (dp_unit.flags & DP_ALPHA)
return;
@ -207,6 +213,27 @@ static void decrement (uint16 *msb, uint16 *lsb, uint16 x)
*lsb &= 037;
}
static int scale_or_one (void)
{
/* On an Alpha machine, the MSB is incremented per the scaling
factor. On a Graphics machine, it's incremented by one
regardless of the scaling factor. */
if (dp_unit.flags & DP_ALPHA)
return SCALE >> 1;
else
return 1;
}
static void load_xy_accumulator (uint16 *msb, uint16 *lsb, uint16 insn)
{
if (dp_unit.flags & DP_ALPHA)
*msb = (insn >> 5) & 0177;
else
*msb = (insn >> 4) & 0077;
*lsb = (insn << 1) & 0036;
}
static t_stat
dp_opr(uint16 insn)
{
@ -255,19 +282,19 @@ dp_opr(uint16 insn)
}
if (insn & 00100) { /* DDYM */
sim_debug (DBG, &dp_dev, "DDYM ");
YMSB--;
YMSB -= scale_or_one ();
}
if (insn & 00200) { /* DDXM */
sim_debug (DBG, &dp_dev, "DDXM ");
XMSB--;
XMSB -= scale_or_one ();
}
if (insn & 00400) { /* DIYM */
sim_debug (DBG, &dp_dev, "DIYM ");
YMSB++;
YMSB += scale_or_one ();
}
if (insn & 01000) { /* DIXM */
sim_debug (DBG, &dp_dev, "DIXM ");
XMSB++;
XMSB += scale_or_one ();
}
if (insn & 02000) { /* DHVC */
sim_debug (DBG, &dp_dev, "DHVC ");
@ -386,13 +413,13 @@ dp_inc_escape (uint16 byte)
sim_debug (DBG, &dp_dev, "stack underflow");
}
if (byte & 020)
XMSB++;
XMSB += scale_or_one ();
if (byte & 010)
XLSB = 0;
if (byte & 4) /* Enter PPM mode. */
;
if (byte & 2)
YMSB++;
YMSB += scale_or_one ();
if (byte & 1)
YLSB = 0;
@ -454,13 +481,11 @@ dp_insn (uint16 insn)
break;
case 1: /* DLXA */
sim_debug (DBG, &dp_dev, "DLXA %04o\n", insn & 01777);
XMSB = (insn >> 4) & 0077;
XLSB = (insn << 1) & 0036;
load_xy_accumulator (&XMSB, &XLSB, insn);
break;
case 2: /* DLYA */
sim_debug (DBG, &dp_dev, "DLYA %04o\n", insn & 01777);
YMSB = (insn >> 4) & 0077;
YLSB = (insn << 1) & 0036;
load_xy_accumulator (&YMSB, &YLSB, insn);
break;
case 3: /* DEIM */
sim_debug (DBG, &dp_dev, "DEIM ");