Benchmark: Don't overflow meter if over 16MHz

The Benchmark accessory uses VBL to gauge the processor speed. The
Virtual ][ emulator version 13.0 decouples VBL from emulation speed,
which is neat; at "high" speed, you can see the CPU runs faster than
1MHz (I see it vary between 0.8MHz and 2MHz). At "maximum" speed it is
way faster than 16MHz, which was overflowing the progress meter!

Add a clamp so that the meter never mis-paints, even at this
ludicrious speed.

Author: inexorabletash

RELEASE-NOTES.md

@@ -80,6 +80,7 @@ Project Page: https://github.com/a2stuff/a2d
   * Refresh windows if 12/24-hour setting changes. ([#835](https://github.com/a2stuff/a2d/issues/835))
   * Refresh windows if date changes. ([#843](https://github.com/a2stuff/a2d/issues/843))
 * International: Add "first day of week" setting.
+* Benchmark: Don't overflow meter if over 16MHz.
 * New DA (in Extras): "Screenshot" - saves screenshot file to application directory.
 * New DA (in Extras): "DOS33.Import" - allows importing files from DOS 3.3 disks.
 * New DA (in Control Panels): "Views" - allows setting the default view style.

src/desk.acc/benchmark.s

@@ -155,6 +155,15 @@ pattern_right:
         .byte   %11111111
         .byte   %10111011
         .byte   %11111111
+pattern_plaid:
+        .byte   %01011010
+        .byte   %11111111
+        .byte   %01011010
+        .byte   %01011010
+        .byte   %01011010
+        .byte   %11111111
+        .byte   %01011010
+        .byte   %01011010
 
         DEFINE_POINT pt_tick, 0, kMeterTop + kMeterHeight + 2
         DEFINE_POINT pt_tickdelta, 0, 2
@@ -349,6 +358,8 @@ done:   jmp     InputLoop
 ;;; ============================================================
 
 .proc UpdateMeter
+        MGTK_CALL MGTK::SetPattern, pattern_left
+
         jsr     ProbeSpeed
 
         copy16  counter, progress_muldiv_params::numerator
@@ -360,11 +371,18 @@ done:   jmp     InputLoop
     END_IF
 
         MGTK_CALL MGTK::MulDiv, progress_muldiv_params
+
+        ;; Max out the meter
+        cmp16   progress_muldiv_params::result, #kMeterWidth
+    IF_GE
+        copy16  #kMeterWidth, progress_muldiv_params::result
+        MGTK_CALL MGTK::SetPattern, pattern_plaid
+    END_IF
+
         add16   meter_left::x1, progress_muldiv_params::result, meter_left::x2
         add16   meter_left::x2, #1, meter_right::x1
 
         MGTK_CALL MGTK::SetPenMode, pencopy
-        MGTK_CALL MGTK::SetPattern, pattern_left
         MGTK_CALL MGTK::PaintRect, meter_left
         MGTK_CALL MGTK::SetPattern, pattern_right
         MGTK_CALL MGTK::PaintRect, meter_right