Improve ET4000 data volume explanation with 32 KB buffer context

retro/et4000-experiment/index.njk

@@ -37,6 +37,27 @@ parent: "/retro/"
 <h2>How It Got Working</h2>
 <p>Solving it came down to giving the supply the headroom it needed. With a properly beefed-up power supply to cover the 5V and 12V rails, plus a cooling solution for the card, the stability problems went away. The ET4000 now drives higher resolutions and more colors than the Shifter chip can natively produce, turning the "High" machine into a genuine workstation.</p>
 
+<h2>GemBench Results</h2>
+<p>How does the ET4000 actually perform on an 8 MHz 68000? GemBench 6.31 gives the answer. The reference system is an STE 68000 with stock Shifter, the "High" machine has the ET4000 running at 1024x768x256.</p>
+<img src="gembench.jpg" alt="GemBench 6.31 results on the ET4000" width="640" height="480" loading="lazy">
+<p class="caption">GemBench 6.31 running on the Mega ST 4 "High" with the ET4000.</p>
+<table>
+<tr><th>Test</th><th>Ratio</th><th>What it means</th></tr>
+<tr><td>VDI Text</td><td>269%</td><td>Nearly 3x faster, the ET4000 handles text rendering</td></tr>
+<tr><td>VDI Small Text</td><td>174%</td><td>Noticeably faster</td></tr>
+<tr><td>VDI Graphics</td><td>188%</td><td>Drawing and line work is quicker</td></tr>
+<tr><td>VDI Enquire</td><td>160%</td><td>Screen queries are faster</td></tr>
+<tr><td>VDI Text Effects</td><td>112%</td><td>Slightly faster</td></tr>
+<tr><td>GEM Dialog Box</td><td>97%</td><td>Barely affected</td></tr>
+<tr><td>Integer Division</td><td>99%</td><td>CPU-bound, unchanged</td></tr>
+<tr><td>RAM / ROM Access</td><td>99%</td><td>CPU-bound, unchanged</td></tr>
+<tr><td>Justified Text</td><td>63%</td><td>Slower, GEM still handles this via CPU</td></tr>
+<tr><td>GEM Window</td><td>69%</td><td>Slower, GEM window management adds overhead</td></tr>
+<tr><td>VDI Scroll</td><td>53%</td><td>Slower, scrolling is CPU-bound despite the card</td></tr>
+<tr><td>Blitting</td><td>32%</td><td>Much slower, no hardware BitBLT on the ET4000</td></tr>
+</table>
+<p>The overall average sits at 100%, which is misleading. The picture is split: anything the ET4000 can accelerate (text, graphics drawing) runs significantly faster, while GEM-level operations that still go through the CPU (window management, scrolling, blitting) are dragged down by the overhead of driving a higher resolution through the adapted ISA bus. Running at 1024x768 with 256 colors means roughly 3x the pixel count and roughly 25x the data volume compared to ST High (640x400 monochrome), since the ST's fixed 32 KB screen buffer holds far less data per frame than a 256-color 1024x768 framebuffer. The Nova driver without NVDI squeezes the maximum out of this particular card and driver combination. In day-to-day use, the VDI gains are what you see and feel: text is crisp, menus pop up quickly, and drawing applications are noticeably more responsive.</p>
+
 <h2>The Context</h2>
 <p>FPGA cores on MiSTer and MiST still only emulate the native ST Shifter, with no ET4000 emulation on the horizon given the FPGA resources it would require. So the real hardware approach remains the only way to get those higher resolutions, and now it works in the Mega ST 4 "High" machine with its dedicated <a href="/retro/atari-monitor-compatibility/">monitor</a>.</p>