Talk: add text for the remaining slides

especially setup the structure of slides to present the demo code.

Publication of Demo Code will be at:
git://git.lumiera.org/extra/video-output.git

Generate a new QR-Code for that URL

FrOSCon26/drawings/coherence.svg

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg"
+     xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+     xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+     width="254.0mm" height="142.9mm" viewBox="0 0 254.0 142.9" version="1.1">
+  <sodipodi:namedview inkscape:document-units="mm" units="mm"/>
+  <title>Cache coherence and observability</title>
+<g inkscape:groupmode="layer" id="layer-1-scaffold" inkscape:label="1 - scaffold (x=0 everywhere)" style="display:inline">
+  <defs><marker id="arrow" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse"><path d="M0,0 L10,5 L0,10 z" fill="#555555"/></marker></defs>
+  <rect x="44.00" y="24.00" width="46.00" height="20.00" rx="2.0" fill="#ffffff" stroke="#222222" stroke-width="0.8"/>
+  <text x="67.00" y="35.80" font-family="DejaVu Sans, Verdana, sans-serif" font-size="5.5" font-weight="600" fill="#222222" text-anchor="middle">Core</text>
+  <rect x="164.00" y="24.00" width="46.00" height="20.00" rx="2.0" fill="#ffffff" stroke="#222222" stroke-width="0.8"/>
+  <text x="187.00" y="35.80" font-family="DejaVu Sans, Verdana, sans-serif" font-size="5.5" font-weight="600" fill="#222222" text-anchor="middle">Core</text>
+  <path d="M 67.00,44.00 L 67.00,58.00" stroke="#555555" stroke-width="0.6" fill="none" marker-end="url(#arrow)"/>
+  <path d="M 187.00,44.00 L 187.00,58.00" stroke="#555555" stroke-width="0.6" fill="none" marker-end="url(#arrow)"/>
+  <path d="M 67.00,80.00 L 67.00,110.00" stroke="#555555" stroke-width="0.6" fill="none"/>
+  <path d="M 67.00,110.00 L 90.00,104.00" stroke="#555555" stroke-width="0.6" fill="none"/>
+  <path d="M 187.00,80.00 L 187.00,110.00" stroke="#555555" stroke-width="0.6" fill="none"/>
+  <path d="M 187.00,110.00 L 164.00,104.00" stroke="#555555" stroke-width="0.6" fill="none"/>
+  <rect x="44.00" y="58.00" width="46.00" height="22.00" rx="2.0" fill="#f2f2f2" stroke="#222222" stroke-width="0.8"/>
+  <rect x="164.00" y="58.00" width="46.00" height="22.00" rx="2.0" fill="#f2f2f2" stroke="#222222" stroke-width="0.8"/>
+  <text x="67.00" y="64.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="4.2" font-weight="600" fill="#222222" text-anchor="middle">Cache</text>
+  <text x="187.00" y="64.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="4.2" font-weight="600" fill="#222222" text-anchor="middle">Cache</text>
+  <text x="67.00" y="74.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="6.5" font-weight="700" fill="#8a8a8a" text-anchor="middle">x = 0</text>
+  <text x="187.00" y="74.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="6.5" font-weight="700" fill="#8a8a8a" text-anchor="middle">x = 0</text>
+  <rect x="82.00" y="104.00" width="90.00" height="24.00" rx="2.0" fill="#f2f2f2" stroke="#222222" stroke-width="0.8"/>
+  <text x="127.00" y="111.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="4.2" font-weight="600" fill="#222222" text-anchor="middle">DRAM</text>
+  <text x="127.00" y="122.50" font-family="DejaVu Sans, Verdana, sans-serif" font-size="6.5" font-weight="700" fill="#8a8a8a" text-anchor="middle">x = 0</text>
+</g>
+<g inkscape:groupmode="layer" id="layer-2-core0-write" inkscape:label="2 - core0 writes x=1" style="display:inline">
+  <rect x="44.00" y="58.00" width="46.00" height="22.00" rx="2.0" fill="#dce8f2" stroke="#14507d" stroke-width="1.1"/>
+  <text x="67.00" y="64.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="4.2" font-weight="600" fill="#222222" text-anchor="middle">Cache</text>
+  <text x="67.00" y="74.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="6.5" font-weight="700" fill="#14507d" text-anchor="middle">x = 1</text>
+</g>
+<g inkscape:groupmode="layer" id="layer-3-core1-read" inkscape:label="3 - core1 reads: still x=0" style="display:inline">
+  <path d="M 184.00,45.50 C 179.00,51.00 179.00,51.00 184.00,56.50" stroke="#8a8a8a" stroke-width="0.6" fill="none" marker-end="url(#arrow)"/>
+  <rect x="164.00" y="58.00" width="46.00" height="22.00" rx="2.0" fill="#f2f2f2" stroke="#8a8a8a" stroke-width="1.1"/>
+  <text x="187.00" y="64.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="4.2" font-weight="600" fill="#222222" text-anchor="middle">Cache</text>
+  <text x="187.00" y="74.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="6.5" font-weight="700" fill="#8a8a8a" text-anchor="middle">x = 0</text>
+</g>
+<g inkscape:groupmode="layer" id="layer-4-propagate" inkscape:label="4 - later: DRAM sees x=1, core1 still stale" style="display:inline">
+  <circle cx="119.0" cy="95.0" r="0.7" fill="#8a8a8a"/><circle cx="123.0" cy="95.0" r="0.7" fill="#8a8a8a"/><circle cx="127.0" cy="95.0" r="0.7" fill="#8a8a8a"/><circle cx="131.0" cy="95.0" r="0.7" fill="#8a8a8a"/><circle cx="135.0" cy="95.0" r="0.7" fill="#8a8a8a"/>
+  <rect x="82.00" y="104.00" width="90.00" height="24.00" rx="2.0" fill="#dce8f2" stroke="#14507d" stroke-width="1.1"/>
+  <text x="127.00" y="111.00" font-family="DejaVu Sans, Verdana, sans-serif" font-size="4.2" font-weight="600" fill="#222222" text-anchor="middle">DRAM</text>
+  <text x="127.00" y="122.50" font-family="DejaVu Sans, Verdana, sans-serif" font-size="6.5" font-weight="700" fill="#14507d" text-anchor="middle">x = 1</text>
+</g>
+</svg>

FrOSCon26/drawings/gen-cache-coherence-diagram.py

@@ -0,0 +1,222 @@
+#!/usr/bin/env python3
+"""Cache coherence / observability diagram.
+
+Four Inkscape layers, meant to be exported one by one (Export > Page) and
+stacked as transparent overlays in Impress, same workflow as the time-scales
+diagram. Layer content is INCREMENTAL: each layer only draws what is new at
+that step; earlier layers stay visible underneath once stacked.
+
+Story:
+  1  scaffold        - two cores, two caches, one shared DRAM, all agree: x=0
+  2  core0-write     - core0's cache changes to x=1; nothing else does
+  3  core1-read      - core1 reads its own cache: still x=0 (stale, not wrong)
+  4  propagate       - some time later, x=1 reaches DRAM on its own;
+                        core1's cache is untouched and still says x=0
+"""
+
+W, H = 254.0, 142.9
+
+# ---- palette (kept consistent with time-scales.svg) -----------------------
+C_LINE   = "#555555"
+C_BOX    = "#222222"
+C_MACH   = "#14507d"     # "new" value / updated state
+C_STALE  = "#8a8a8a"     # stale / unchanged value
+C_FILL0  = "#f2f2f2"     # box fill, neutral state
+C_FILL1  = "#dce8f2"     # box fill, updated state
+C_WHITE  = "#ffffff"
+FONT = "DejaVu Sans, Verdana, sans-serif"
+
+F_LABEL, F_VALUE, F_TAG = 5.5, 6.5, 4.2
+
+# ---- geometry ---------------------------------------------------------
+CORE_W, CORE_H = 46.0, 20.0
+CACHE_W, CACHE_H = 46.0, 22.0
+DRAM_W, DRAM_H = 90.0, 24.0
+
+CORE0_X, CORE1_X = 44.0, 164.0
+CORE_Y   = 24.0
+CACHE_Y  = 58.0
+DRAM_X   = (W - DRAM_W) / 2.0
+DRAM_Y   = 104.0
+
+C0_CX = CORE0_X + CORE_W / 2.0
+C1_CX = CORE1_X + CORE_W / 2.0
+DRAM_CX = DRAM_X + DRAM_W / 2.0
+
+
+def esc(s):
+    return s.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+
+
+def text(x, y, s, size, fill, anchor="middle", weight="normal", family=FONT):
+    return (f'<text x="{x:.2f}" y="{y:.2f}" font-family="{family}" '
+            f'font-size="{size}" font-weight="{weight}" fill="{fill}" '
+            f'text-anchor="{anchor}">{esc(s)}</text>')
+
+
+def rect(x, y, w, h, fill, stroke, sw=0.6, rx=2.0):
+    return (f'<rect x="{x:.2f}" y="{y:.2f}" width="{w:.2f}" height="{h:.2f}" '
+            f'rx="{rx}" fill="{fill}" stroke="{stroke}" stroke-width="{sw}"/>')
+
+
+def line(x1, y1, x2, y2, stroke=C_LINE, w=0.6, dash=None, marker=False):
+    d = f' stroke-dasharray="{dash}"' if dash else ""
+    m = ' marker-end="url(#arrow)"' if marker else ""
+    return (f'<path d="M {x1:.2f},{y1:.2f} L {x2:.2f},{y2:.2f}" '
+            f'stroke="{stroke}" stroke-width="{w}" fill="none"{d}{m}/>')
+
+
+def defs():
+    return ('<defs><marker id="arrow" viewBox="0 0 10 10" refX="8" refY="5" '
+            'markerWidth="6" markerHeight="6" orient="auto-start-reverse">'
+            f'<path d="M0,0 L10,5 L0,10 z" fill="{C_LINE}"/></marker></defs>')
+
+
+# ==========================================================================
+# static structural pieces, reused across layers where needed
+# ==========================================================================
+def core_box(cx_left, label_suffix=""):
+    cx = cx_left + CORE_W / 2.0
+    o = [rect(cx_left, CORE_Y, CORE_W, CORE_H, C_WHITE, C_BOX, 0.8)]
+    o.append(text(cx, CORE_Y + CORE_H / 2.0 + 1.8, "Core", F_LABEL, C_BOX,
+                  weight="600"))
+    return o
+
+
+def cache_box_frame(cx_left):
+    return [rect(cx_left, CACHE_Y, CACHE_W, CACHE_H, C_FILL0, C_BOX, 0.8)]
+
+
+def cache_tag(cx_left):
+    cx = cx_left + CACHE_W / 2.0
+    return [text(cx, CACHE_Y + 6.0, "Cache", F_TAG, C_BOX, weight="600")]
+
+
+def cache_value(cx_left, value_str, colour):
+    cx = cx_left + CACHE_W / 2.0
+    return [text(cx, CACHE_Y + CACHE_H / 2.0 + 5.0, value_str, F_VALUE, colour,
+                 weight="700")]
+
+
+def dram_box_frame():
+    return [rect(DRAM_X, DRAM_Y, DRAM_W, DRAM_H, C_FILL0, C_BOX, 0.8)]
+
+
+def dram_tag():
+    return [text(DRAM_CX, DRAM_Y + 7.0, "DRAM", F_TAG, C_BOX, weight="600")]
+
+
+def dram_value(value_str, colour):
+    return [text(DRAM_CX, DRAM_Y + DRAM_H / 2.0 + 6.5, value_str, F_VALUE,
+                 colour, weight="700")]
+
+
+def bus_lines():
+    o = []
+    o.append(line(C0_CX, CORE_Y + CORE_H, C0_CX, CACHE_Y, marker=True))
+    o.append(line(C1_CX, CORE_Y + CORE_H, C1_CX, CACHE_Y, marker=True))
+    o.append(line(C0_CX, CACHE_Y + CACHE_H, C0_CX, DRAM_Y + 6.0, C_LINE, 0.6))
+    o.append(line(C0_CX, DRAM_Y + 6.0, DRAM_X + 8.0, DRAM_Y, C_LINE, 0.6))
+    o.append(line(C1_CX, CACHE_Y + CACHE_H, C1_CX, DRAM_Y + 6.0, C_LINE, 0.6))
+    o.append(line(C1_CX, DRAM_Y + 6.0, DRAM_X + DRAM_W - 8.0, DRAM_Y, C_LINE, 0.6))
+    return o
+
+
+# ==========================================================================
+#  layer 1 - scaffold: full structure, everyone agrees x = 0
+# ==========================================================================
+def layer1():
+    o = [defs()]
+    o += core_box(CORE0_X)
+    o += core_box(CORE1_X)
+    o += bus_lines()
+    o += cache_box_frame(CORE0_X)
+    o += cache_box_frame(CORE1_X)
+    o += cache_tag(CORE0_X)
+    o += cache_tag(CORE1_X)
+    o += cache_value(CORE0_X, "x = 0", C_STALE)
+    o += cache_value(CORE1_X, "x = 0", C_STALE)
+    o += dram_box_frame()
+    o += dram_tag()
+    o += dram_value("x = 0", C_STALE)
+    return o
+
+
+# ==========================================================================
+#  layer 2 - core0 writes: only its own cache changes
+# ==========================================================================
+def layer2():
+    o = []
+    # cover old value + box fill with an updated-state box, then new value
+    o.append(rect(CORE0_X, CACHE_Y, CACHE_W, CACHE_H, C_FILL1, C_MACH, 1.1))
+    o += cache_tag(CORE0_X)
+    o += cache_value(CORE0_X, "x = 1", C_MACH)
+    return o
+
+
+# ==========================================================================
+#  layer 3 - core1 reads its own cache: emphasise the access, value unchanged
+# ==========================================================================
+def layer3():
+    o = []
+    cx = CORE1_X + CACHE_W / 2.0
+    # small self-loop "read" arrow from core1 down into its own cache
+    top = CORE_Y + CORE_H + 1.5
+    bot = CACHE_Y - 1.5
+    r = 5.0
+    o.append(f'<path d="M {cx-3:.2f},{top:.2f} '
+             f'C {cx-3-r:.2f},{(top+bot)/2:.2f} {cx-3-r:.2f},{(top+bot)/2:.2f} '
+             f'{cx-3:.2f},{bot:.2f}" stroke="{C_STALE}" stroke-width="0.6" '
+             f'fill="none" marker-end="url(#arrow)"/>')
+    o.append(rect(CORE1_X, CACHE_Y, CACHE_W, CACHE_H, C_FILL0, C_STALE, 1.1))
+    o += cache_tag(CORE1_X)
+    o += cache_value(CORE1_X, "x = 0", C_STALE)
+    return o
+
+
+# ==========================================================================
+#  layer 4 - later, unobserved: x = 1 reaches DRAM; core1 still stale
+# ==========================================================================
+def layer4():
+    o = []
+    # a faint "time passing" mark between the structure and nothing else
+    ty = DRAM_Y - 9.0
+    dots = "".join(f'<circle cx="{DRAM_CX-8+4*i:.1f}" cy="{ty:.1f}" r="0.7" '
+                    f'fill="{C_STALE}"/>' for i in range(5))
+    o.append(dots)
+    o.append(rect(DRAM_X, DRAM_Y, DRAM_W, DRAM_H, C_FILL1, C_MACH, 1.1))
+    o += dram_tag()
+    o += dram_value("x = 1", C_MACH)
+    return o
+
+
+# ==========================================================================
+def layer(lid, label, body, display="inline"):
+    return (f'<g inkscape:groupmode="layer" id="{lid}" '
+            f'inkscape:label="{label}" style="display:{display}">\n  '
+            + "\n  ".join(body) + "\n</g>")
+
+
+def build():
+    layers = [
+        layer("layer-1-scaffold", "1 - scaffold (x=0 everywhere)", layer1()),
+        layer("layer-2-core0-write", "2 - core0 writes x=1", layer2()),
+        layer("layer-3-core1-read", "3 - core1 reads: still x=0", layer3()),
+        layer("layer-4-propagate", "4 - later: DRAM sees x=1, core1 still stale",
+              layer4()),
+    ]
+    return f'''<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg"
+     xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+     xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+     width="{W}mm" height="{H}mm" viewBox="0 0 {W} {H}" version="1.1">
+  <sodipodi:namedview inkscape:document-units="mm" units="mm"/>
+  <title>Cache coherence and observability</title>
+{chr(10).join(layers)}
+</svg>
+'''
+
+
+if __name__ == "__main__":
+    open("/mnt/user-data/outputs/coherence.svg", "w").write(build())
+    print("written")

FrOSCon26/examples/demo-uring.cpp

@@ -203,6 +203,9 @@ UringVideoPlayer::addNextReadSubmissions (io_uring& uRing, int inputFD)
     {
       size_t srcOffset = calcSrcFrame (nextRead_);
       io_uring_sqe* readSubmission = io_uring_get_sqe (&uRing);
+      if (nullptr == readSubmission)
+        __FAIL ("URing slot allocation failed");
+
       io_uring_prep_read (readSubmission
                          ,inputFD
                          ,& buffer_[nextRead_ % RING_SIZ]

FrOSCon26/examples/egl-display.hpp

@@ -45,7 +45,7 @@ class EglDisplay
     using Buffer = std::array<PIX, WIDTH*HEIGHT * 3 >;
 
     /**
-     * Interface retrieve pixel data for video frames to display.
+     * Interface: retrieve pixel data for video frames to display.
      * - this is a Glib::Dispatcher, and the attached slot shall be
      *   triggered whenever data for a new frame is available
      * - pixel data is accessed (threadsafe) by invoking #retrieveFrame()
@@ -85,7 +85,7 @@ class EglDisplay
     float scaleX_{1};
     float scaleY_{1};
 
-    /** Callback functor to access current pixel data */
+    /** Callback to retrieve pixel data */
     PixelFeed& pixelFeed_{};
 
     void openDisplay (Gtk::Window&);