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IMLAC: Implement 8-level return stack for display processor.

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Needed by Maze.
This commit is contained in:
Lars Brinkhoff
2020-06-14 18:50:48 +02:00
parent 582afd9250
commit 50266704ca
1 changed files with 19 additions and 6 deletions
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25
imlac/imlac_dp.c
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@@ -30,7 +30,8 @@
#define DBG 0001
static t_addr DPC;
static t_addr DT;
static t_addr DT[8];
static uint16 SP = 0;
static uint16 ON = 0;
static uint16 HALT = 0;
static uint16 MODE = 0;
@@ -63,7 +64,8 @@ static REG dp_reg[] = {
{ ORDATAD (ON, ON, 1, "Display on") },
{ ORDATAD (HALT, HALT, 1, "Display halted") },
{ ORDATAD (MODE, MODE, 1, "Display mode") },
{ ORDATAD (DT, DT, 16, "Return address") },
{ BRDATAD (DT, DT, 8, 16, 8, "Return address stack") },
{ ORDATAD (SP, SP, 3, "Stack pointer") },
{ ORDATAD (XA, XA, 11, "X accumulator") },
{ ORDATAD (YA, YA, 11, "Y accumulator") },
{ ORDATAD (SCALE, SCALE, 3, "Scale") },
@@ -118,6 +120,7 @@ void
dp_on (int flag)
{
if (!ON && flag) {
SP = 0;
MIT8K = 0;
sim_activate_abs (&dp_unit, 0);
sim_debug (DBG, &dp_dev, "Display on\n");
@@ -201,7 +204,10 @@ dp_opr(uint16 insn)
}
if (insn & 00040) { /* DRJM */
sim_debug (DBG, &dp_dev, "DRJM ");
DPC = DT;
if (SP > 0)
DPC = DT[--SP];
else
sim_debug (DBG, &dp_dev, "stack underflow");
}
if (insn & 00100) { /* DDYM */
sim_debug (DBG, &dp_dev, "DDYM ");
@@ -330,8 +336,12 @@ dp_inc_escape (uint16 byte)
if (byte & 0100)
MODE = 0;
if (byte & 040)
DPC = DT;
if (byte & 040) {
if (SP > 0)
DPC = DT[--SP];
else
sim_debug (DBG, &dp_dev, "stack underflow");
}
if (byte & 020)
XA += 040;
if (byte & 010)
@@ -417,7 +427,10 @@ dp_insn (uint16 insn)
break;
case 5: /* DJMS */
sim_debug (DBG, &dp_dev, "DJMS\n");
DT = DPC;
if (SP < 7)
DT[SP++] = DPC;
else
sim_debug (DBG, &dp_dev, "stack overflow");
/* Fall through. */
case 6: /* DJMP */
sim_debug (DBG, &dp_dev, "DJMP\n");