harness: configurable board model busy timings + findings

harness/mame/test_vt1200_board.cpp

@@ -100,6 +100,28 @@ static void test_dma_pair_command_completes(void)
     CHECK(b.read(VT1200_WIN1) == 0x0000);    // completed
 }
 
+// The two timers the sweep tunes (window busy and DMA completion) must advance
+// on the same tick(), or a later slower timer would silently stretch the other.
+static void test_one_tick_advances_window_and_dma_timers(void)
+{
+    vt1200_board b;
+    b.set_model_handshake(true);
+    b.set_window_busy_ticks(VT1200_WIN2, 2);
+    b.set_dma_ticks(2);
+
+    b.write(VT1200_WIN2 + VT1200_OFF_CMD, 0x0001);   // arms WIN2's busy bit
+    b.write(VT1200_WIN0, 0x0000);                    // data port first
+    b.write(VT1200_WIN1, 0x0042);                    // then a DMA command
+
+    b.tick();                                        // one frame: both advance
+    CHECK((b.read(VT1200_WIN2 + VT1200_OFF_STATUS) & 1) == 1);
+    CHECK(b.read(VT1200_WIN1) == 0x0042);
+
+    b.tick();
+    CHECK((b.read(VT1200_WIN2 + VT1200_OFF_STATUS) & 1) == 0);
+    CHECK(b.read(VT1200_WIN1) == 0x0000);
+}
+
 int main(void)
 {
     test_default_read();
@@ -110,6 +132,7 @@ int main(void)
     test_monitor_switch_accepts_raw_bits_or_position();
     test_switch_mix_only_when_configured();
     test_dma_pair_command_completes();
+    test_one_tick_advances_window_and_dma_timers();
     std::printf(failures ? "%d FAILURE(S)\n" : "all board tests passed\n", failures);
     return failures ? 1 : 0;
 }