From 2498fafd4681179e031c25ed11e9c6ad00adafcd Mon Sep 17 00:00:00 2001
From: Mark Pizzolato <mark@infocomm.com>
Date: Tue, 26 Apr 2016 12:32:13 -0700
Subject: [PATCH] MicroVAX II, rtVAX1000: Fix NVR behavior to precisely reflect
 original hardware

Observations made about NVR behavior on real hardware:
    1) Aligned writes only affect a single RAM location
       without regard to the size of write, so no double
       pumping on writes.
    2) Unaligned (offset 3) writes do nothing without regard to size of the write
    3) Unaligned (offset 1) write 0 to the next higher NVR RAM location.
    4) Longword aligned and Unaligned (offset 3) reads return the same NVR RAM
       value in the the upper and lower words of the result.
    5) Unaligned (offset 1) reads reference the next higher NVR RAM cell for
       word and longword reads.

- Fix write behavior to match hardware.
- Fix read behavior to double pump word values for all unaligned word and longword
  reads.
---
 VAX/vax630_sysdev.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/VAX/vax630_sysdev.c b/VAX/vax630_sysdev.c
index a0b4a1ff..a5691c87 100644
--- a/VAX/vax630_sysdev.c
+++ b/VAX/vax630_sysdev.c
@@ -27,7 +27,7 @@
    This module contains the MicroVAX II system-specific registers and devices.
 
    rom          bootstrap ROM (no registers)
-   nvr          non-volatile ROM (no registers)
+   nvr          non-volatile RAM (no registers)
    sysd         system devices
 
    08-Nov-2012  MB      First version
@@ -431,16 +431,16 @@ return "read-only memory";
 
 int32 nvr_rd (int32 pa)
 {
-int32 rg = (pa - NVRBASE) >> 1;
+int32 rg = (pa + 1 - NVRBASE) >> 1;
 int32 result;
 
 if (rg < 14)                                             /* watch chip */
     result = wtc_rd (pa);
-else
-    if (rg & 1)
-        result = ((int32)nvr[rg]) << 16;
-    else
-        result = nvr[rg] | (((int32)nvr[rg+1]) << 16);
+else {
+    result = (nvr[rg] & WMASK) | (((uint32)nvr[rg]) << 16);
+    if (pa & 1)
+        result = result << 8;
+    }
 
 sim_debug (DBG_REG, &nvr_dev, "nvr_rd(pa=0x%X) nvr[0x%X] returns: 0x%X\n", pa, rg, result);
 
@@ -449,21 +449,21 @@ return result;
 
 void nvr_wr (int32 pa, int32 val, int32 lnt)
 {
-int32 rg = (pa - NVRBASE) >> 1;
+int32 rg = (pa + 1 - NVRBASE) >> 1;
 
 if (rg < 14)                                             /* watch chip */
     wtc_wr (pa, val, lnt);
 else {
     int32 orig_nvr = (int32)nvr[rg];
-    int32 v = val;
-    int32 r = rg;
-    int32 l = lnt;
 
-    while (l > 0) {
-        nvr[r] = (uint8)v;
-        ++r;
-        l -= 2;
-        v = (v >> 16);
+    switch (pa & 03) {
+        case 0:
+        case 2:
+            nvr[rg] = (uint8)val;
+            break;
+        case 1:
+            nvr[rg] = 0;
+            break;
         }
 
     if (lnt > 1)
@@ -784,7 +784,9 @@ MACH_CHECK (MCHK_READ);
 
 int32 ReadRegU (uint32 pa, int32 lnt)
 {
-return ReadReg (pa & ~03, L_LONG);
+if (lnt == L_BYTE)
+    return ReadReg (pa & ~03, L_LONG);
+return (ReadReg (pa & ~03, L_WORD) & WMASK) | (ReadReg ((pa & ~03) + 2, L_WORD) & (WMASK << 16));
 }
 
 /* WriteReg - write register space