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Merge branch 'fix/mcpwm_cap_prescale_v5.4' into 'release/v5.4'
fix(mcpwm): correct the wrong capture prescale (v5.4) See merge request espressif/esp-idf!52507
This commit is contained in:
morris
74
docs/_static/mcpwm/capture_prescale_both.svg
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74
docs/_static/mcpwm/capture_prescale_both.svg
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<?xml version="1.0" encoding="UTF-8"?>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 700 440" font-family="'DejaVu Sans Mono', 'Consolas', 'Liberation Mono', monospace">
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<rect width="700" height="440" fill="#ffffff" rx="8"/>
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<text x="350" y="24" text-anchor="middle" font-size="13" fill="#333" font-weight="700">Both edges</text>
|
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<text x="350" y="42" text-anchor="middle" font-size="10" fill="#666">API prescale = same-edge ratio</text>
|
||||
|
||||
<text x="20" y="68" font-size="12" fill="#333" font-weight="700">A. prescale = 1 (bypass)</text>
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<g transform="translate(80, 78)">
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<text x="-10" y="36" text-anchor="end" font-size="11" fill="#1e88e5" font-weight="600">input</text>
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<polyline fill="none" stroke="#1e88e5" stroke-width="2"
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points="0,40 0,12 35,12 35,40 70,40 70,12 105,12 105,40 140,40 140,12 175,12 175,40 210,40"/>
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<g fill="#e53935"><circle cx="0" cy="12" r="3.5"/><circle cx="70" cy="12" r="3.5"/><circle cx="140" cy="12" r="3.5"/></g>
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<g fill="#fb8c00"><rect x="31" y="8" width="8" height="8"/><rect x="101" y="8" width="8" height="8"/><rect x="171" y="8" width="8" height="8"/></g>
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<text x="-10" y="100" text-anchor="end" font-size="11" fill="#333" font-weight="600">capture</text>
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<line x1="0" y1="92" x2="210" y2="92" stroke="#999" stroke-width="1.5"/>
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<line x1="0" y1="12" x2="0" y2="92" stroke="#e53935" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="35" y1="40" x2="35" y2="92" stroke="#fb8c00" stroke-width="1" stroke-dasharray="3,3"/>
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<polyline points="70,92 70,72 82,72 82,92" fill="none" stroke="#e53935" stroke-width="2"/>
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<polyline points="105,92 105,72 117,72 117,92" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<text x="6" y="66" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
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<text x="41" y="66" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<text x="76" y="66" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
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<text x="111" y="66" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<text x="250" y="36" font-size="10" fill="#e53935" font-weight="600">R = GPIO rising</text>
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<text x="250" y="54" font-size="10" fill="#fb8c00" font-weight="600">F = GPIO falling</text>
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</g>
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<text x="20" y="228" font-size="12" fill="#333" font-weight="700">B. prescale = 4</text>
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<g transform="translate(80, 250)">
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<text x="-10" y="36" text-anchor="end" font-size="11" fill="#1e88e5" font-weight="600">input</text>
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<polyline fill="none" stroke="#1e88e5" stroke-width="2"
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points="0,40 0,12 35,12 35,40 70,40 70,12 105,12 105,40 140,40 140,12 175,12 175,40 210,40 210,12 245,12 245,40 280,40 280,12 315,12 315,40 350,40 350,12 385,12 385,40 420,40 420,12 455,12 455,40 490,40 490,12"/>
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<!-- first at cycle 1, then every 2: 1(R),3(F),5(R),7(F) -->
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<g fill="#1e88e5"><circle cx="70" cy="12" r="3.5"/><circle cx="210" cy="12" r="3.5"/><circle cx="350" cy="12" r="3.5"/><circle cx="490" cy="12" r="3.5"/></g>
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<g fill="#bbb"><circle cx="0" cy="12" r="3"/><circle cx="140" cy="12" r="3"/><circle cx="280" cy="12" r="3"/><circle cx="420" cy="12" r="3"/></g>
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<g fill="#ccc"><rect x="31" y="8" width="8" height="8"/><rect x="101" y="8" width="8" height="8"/><rect x="171" y="8" width="8" height="8"/><rect x="241" y="8" width="8" height="8"/><rect x="311" y="8" width="8" height="8"/><rect x="381" y="8" width="8" height="8"/><rect x="451" y="8" width="8" height="8"/></g>
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<text x="70" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 1</text>
|
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<text x="210" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 3</text>
|
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<text x="350" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 5</text>
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<text x="490" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 7</text>
|
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<text x="-10" y="100" text-anchor="end" font-size="11" fill="#333" font-weight="600">capture</text>
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<line x1="0" y1="92" x2="490" y2="92" stroke="#999" stroke-width="1.5"/>
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<line x1="70" y1="12" x2="70" y2="92" stroke="#e53935" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="210" y1="12" x2="210" y2="92" stroke="#fb8c00" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="350" y1="12" x2="350" y2="92" stroke="#e53935" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="490" y1="12" x2="490" y2="92" stroke="#fb8c00" stroke-width="1" stroke-dasharray="3,3"/>
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<polyline points="70,92 70,70 82,70 82,92" fill="none" stroke="#e53935" stroke-width="2"/>
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<polyline points="210,92 210,70 222,70 222,92" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<polyline points="350,92 350,70 362,70 362,92" fill="none" stroke="#e53935" stroke-width="2"/>
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<polyline points="490,92 490,70 502,70 502,92" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<text x="76" y="64" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
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<text x="216" y="64" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<text x="356" y="64" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
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<text x="496" y="64" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<line x1="70" y1="110" x2="70" y2="120" stroke="#666"/><line x1="210" y1="110" x2="210" y2="120" stroke="#666"/>
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<line x1="70" y1="115" x2="210" y2="115" stroke="#666" stroke-width="1.5" marker-end="url(#arr)"/>
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<text x="140" y="134" text-anchor="middle" font-size="10" fill="#666" font-weight="600">adj = 2 x T = (prescale/2) x T</text>
|
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|
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<line x1="70" y1="144" x2="70" y2="154" stroke="#e53935"/><line x1="350" y1="144" x2="350" y2="154" stroke="#e53935"/>
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<line x1="70" y1="149" x2="350" y2="149" stroke="#e53935" stroke-width="1.5" marker-end="url(#arr)"/>
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<text x="210" y="168" text-anchor="middle" font-size="11" fill="#e53935" font-weight="600">R-to-R = 4 x T = prescale x T</text>
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</g>
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</svg>
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|
After Width: | Height: | Size: 6.5 KiB |
61
docs/_static/mcpwm/capture_prescale_falling.svg
vendored
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61
docs/_static/mcpwm/capture_prescale_falling.svg
vendored
Normal file
@@ -0,0 +1,61 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 700 420" font-family="'DejaVu Sans Mono', 'Consolas', 'Liberation Mono', monospace">
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<rect width="700" height="420" fill="#ffffff" rx="8"/>
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<text x="350" y="24" text-anchor="middle" font-size="13" fill="#333" font-weight="700">Falling-edge only</text>
|
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<text x="350" y="42" text-anchor="middle" font-size="10" fill="#666">API prescale = same-edge ratio</text>
|
||||
|
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<text x="20" y="68" font-size="12" fill="#333" font-weight="700">A. prescale = 1 (bypass)</text>
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<g transform="translate(80, 78)">
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<text x="-10" y="36" text-anchor="end" font-size="11" fill="#1e88e5" font-weight="600">input</text>
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<polyline fill="none" stroke="#1e88e5" stroke-width="2"
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points="0,40 0,12 35,12 35,40 70,40 70,12 105,12 105,40 140,40 140,12 175,12 175,40 210,40"/>
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<g fill="#ccc"><circle cx="0" cy="12" r="3"/><circle cx="70" cy="12" r="3"/><circle cx="140" cy="12" r="3"/></g>
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<text x="-10" y="100" text-anchor="end" font-size="11" fill="#fb8c00" font-weight="600">capture</text>
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<line x1="35" y1="40" x2="35" y2="92" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="175" y1="40" x2="175" y2="92" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<polyline points="35,92 35,72 47,72 47,92" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<polyline points="105,92 105,72 117,72 117,92" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<polyline points="175,92 175,72 187,72 187,92" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<text x="41" y="66" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<text x="111" y="66" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<text x="181" y="66" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
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<text x="250" y="40" font-size="10" fill="#555">Every falling edge -> F</text>
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<text x="250" y="58" font-size="10" fill="#888">Rising edges ignored</text>
|
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</g>
|
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|
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<text x="20" y="228" font-size="12" fill="#333" font-weight="700">B. prescale = 4</text>
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<g transform="translate(80, 250)">
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<text x="-10" y="36" text-anchor="end" font-size="11" fill="#1e88e5" font-weight="600">input</text>
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<polyline fill="none" stroke="#1e88e5" stroke-width="2"
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points="0,40 0,12 35,12 35,40 70,40 70,12 105,12 105,40 140,40 140,12 175,12 175,40 210,40 210,12 245,12 245,40 280,40 280,12 315,12 315,40 350,40 350,12 385,12 385,40 420,40 420,12 455,12 455,40 490,40 490,12"/>
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<!-- first at cycle 3, then every 4: cycle 3, 7 -->
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<g fill="#1e88e5"><circle cx="210" cy="12" r="3.5"/><circle cx="490" cy="12" r="3.5"/></g>
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<g fill="#bbb"><circle cx="0" cy="12" r="3"/><circle cx="70" cy="12" r="3"/><circle cx="140" cy="12" r="3"/><circle cx="280" cy="12" r="3"/><circle cx="350" cy="12" r="3"/><circle cx="420" cy="12" r="3"/></g>
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<g fill="#ccc"><rect x="31" y="8" width="8" height="8"/><rect x="101" y="8" width="8" height="8"/><rect x="171" y="8" width="8" height="8"/><rect x="241" y="8" width="8" height="8"/><rect x="311" y="8" width="8" height="8"/><rect x="381" y="8" width="8" height="8"/><rect x="451" y="8" width="8" height="8"/></g>
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<text x="210" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 3</text>
|
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<text x="490" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 7</text>
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<line x1="0" y1="52" x2="70" y2="52" stroke="#bbb" stroke-width="1"/>
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<line x1="0" y1="48" x2="0" y2="56" stroke="#bbb"/><line x1="70" y1="48" x2="70" y2="56" stroke="#bbb"/>
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<text x="35" y="68" text-anchor="middle" font-size="10" fill="#888">T</text>
|
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<text x="-10" y="108" text-anchor="end" font-size="11" fill="#fb8c00" font-weight="600">capture</text>
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<line x1="0" y1="100" x2="490" y2="100" stroke="#fb8c00" stroke-width="1.5"/>
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<line x1="210" y1="12" x2="210" y2="100" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="490" y1="12" x2="490" y2="100" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<polyline points="210,100 210,80 222,80 222,100" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<polyline points="490,100 490,80 502,80 502,100" fill="none" stroke="#fb8c00" stroke-width="2"/>
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<text x="216" y="74" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
|
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<text x="496" y="74" text-anchor="middle" font-size="10" fill="#fb8c00" font-weight="700">F</text>
|
||||
<text x="350" y="90" text-anchor="middle" font-size="10" fill="#555">first = prescale - 1, then every 4</text>
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<line x1="210" y1="118" x2="210" y2="130" stroke="#333"/><line x1="490" y1="118" x2="490" y2="130" stroke="#333"/>
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<line x1="210" y1="124" x2="490" y2="124" stroke="#333" stroke-width="1.5" marker-end="url(#arr)"/>
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<text x="350" y="146" text-anchor="middle" font-size="11" fill="#333" font-weight="600">same-edge = 4 x T = prescale x T</text>
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</g>
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</svg>
|
||||
|
After Width: | Height: | Size: 5.4 KiB |
60
docs/_static/mcpwm/capture_prescale_rising.svg
vendored
Normal file
60
docs/_static/mcpwm/capture_prescale_rising.svg
vendored
Normal file
@@ -0,0 +1,60 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 700 400" font-family="'DejaVu Sans Mono', 'Consolas', 'Liberation Mono', monospace">
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</defs>
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<rect width="700" height="400" fill="#ffffff" rx="8"/>
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<text x="350" y="24" text-anchor="middle" font-size="13" fill="#333" font-weight="700">Rising-edge only</text>
|
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<text x="350" y="42" text-anchor="middle" font-size="10" fill="#666">API prescale = same-edge ratio</text>
|
||||
|
||||
<text x="20" y="68" font-size="12" fill="#333" font-weight="700">A. prescale = 1 (bypass)</text>
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<g transform="translate(80, 78)">
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<text x="-10" y="36" text-anchor="end" font-size="11" fill="#1e88e5" font-weight="600">input</text>
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<polyline fill="none" stroke="#1e88e5" stroke-width="2"
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points="0,40 0,12 35,12 35,40 70,40 70,12 105,12 105,40 140,40 140,12 175,12 175,40 210,40"/>
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<g fill="#1e88e5"><circle cx="0" cy="12" r="3.5"/><circle cx="70" cy="12" r="3.5"/><circle cx="140" cy="12" r="3.5"/></g>
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<g fill="#ccc"><rect x="31" y="8" width="8" height="8"/><rect x="101" y="8" width="8" height="8"/><rect x="171" y="8" width="8" height="8"/></g>
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<text x="-10" y="100" text-anchor="end" font-size="11" fill="#e53935" font-weight="600">capture</text>
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<line x1="0" y1="92" x2="210" y2="92" stroke="#e53935" stroke-width="1.5"/>
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<line x1="0" y1="12" x2="0" y2="92" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="70" y1="12" x2="70" y2="92" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<line x1="140" y1="12" x2="140" y2="92" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
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<polyline points="0,92 0,72 12,72 12,92" fill="none" stroke="#e53935" stroke-width="2"/>
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<polyline points="70,92 70,72 82,72 82,92" fill="none" stroke="#e53935" stroke-width="2"/>
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<polyline points="140,92 140,72 152,72 152,92" fill="none" stroke="#e53935" stroke-width="2"/>
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<text x="6" y="66" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
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<text x="76" y="66" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
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<text x="146" y="66" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
|
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<text x="250" y="40" font-size="10" fill="#555">Every rising edge -> R</text>
|
||||
<text x="250" y="58" font-size="10" fill="#888">Falling edges ignored</text>
|
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</g>
|
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|
||||
<text x="20" y="228" font-size="12" fill="#333" font-weight="700">B. prescale = 4</text>
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<g transform="translate(80, 250)">
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<text x="-10" y="36" text-anchor="end" font-size="11" fill="#1e88e5" font-weight="600">input</text>
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<polyline fill="none" stroke="#1e88e5" stroke-width="2"
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points="0,40 0,12 35,12 35,40 70,40 70,12 105,12 105,40 140,40 140,12 175,12 175,40 210,40 210,12 245,12 245,40 280,40 280,12 315,12 315,40 350,40 350,12 385,12 385,40 420,40 420,12"/>
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<!-- first at cycle 1, then every 4: cycle 1, 5 -->
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<g fill="#bbb"><circle cx="0" cy="12" r="3"/><circle cx="140" cy="12" r="3"/><circle cx="210" cy="12" r="3"/><circle cx="280" cy="12" r="3"/><circle cx="420" cy="12" r="3"/></g>
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<g fill="#1e88e5"><circle cx="70" cy="12" r="3.5"/><circle cx="350" cy="12" r="3.5"/></g>
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<text x="70" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 1</text>
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||||
<text x="350" y="-4" text-anchor="middle" font-size="9" fill="#1e88e5" font-weight="700">cycle 5</text>
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<line x1="0" y1="52" x2="70" y2="52" stroke="#bbb" stroke-width="1"/>
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<line x1="0" y1="48" x2="0" y2="56" stroke="#bbb"/><line x1="70" y1="48" x2="70" y2="56" stroke="#bbb"/>
|
||||
<text x="35" y="68" text-anchor="middle" font-size="10" fill="#888">T</text>
|
||||
<text x="-10" y="108" text-anchor="end" font-size="11" fill="#e53935" font-weight="600">capture</text>
|
||||
<line x1="0" y1="100" x2="420" y2="100" stroke="#e53935" stroke-width="1.5"/>
|
||||
<line x1="70" y1="12" x2="70" y2="100" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
|
||||
<line x1="350" y1="12" x2="350" y2="100" stroke="#ccc" stroke-width="1" stroke-dasharray="3,3"/>
|
||||
<polyline points="70,100 70,80 82,80 82,100" fill="none" stroke="#e53935" stroke-width="2"/>
|
||||
<polyline points="350,100 350,80 362,80 362,100" fill="none" stroke="#e53935" stroke-width="2"/>
|
||||
<text x="76" y="74" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
|
||||
<text x="356" y="74" text-anchor="middle" font-size="10" fill="#e53935" font-weight="700">R</text>
|
||||
<text x="210" y="90" text-anchor="middle" font-size="10" fill="#555">first = prescale/2 - 1, then every 4</text>
|
||||
<line x1="70" y1="118" x2="70" y2="130" stroke="#333"/><line x1="350" y1="118" x2="350" y2="130" stroke="#333"/>
|
||||
<line x1="70" y1="124" x2="350" y2="124" stroke="#333" stroke-width="1.5" marker-end="url(#arr)"/>
|
||||
<text x="210" y="146" text-anchor="middle" font-size="11" fill="#333" font-weight="600">same-edge = 4 x T = prescale x T</text>
|
||||
</g>
|
||||
</svg>
|
||||
|
After Width: | Height: | Size: 5.0 KiB |
@@ -936,6 +936,49 @@ The parameter ``user_data`` of :cpp:func:`mcpwm_capture_channel_register_event_c
|
||||
|
||||
This function will lazy install interrupt service for the MCPWM capture channel, whereas the service can only be removed in :cpp:type:`mcpwm_del_capture_channel`.
|
||||
|
||||
Input Prescale
|
||||
~~~~~~~~~~~~~~
|
||||
|
||||
The capture channel processes the input in a **fixed, serial** order:
|
||||
|
||||
1. **First** divide the GPIO waveform by ``prescale`` (``0`` or ``1`` means bypass);
|
||||
2. **Then** use ``pos_edge``/``neg_edge`` to decide which post-prescale events are reported to software.
|
||||
|
||||
So hardware does **not** first filter physical GPIO edges by polarity and only then divide them. With ``prescale > 1``:
|
||||
|
||||
- The :cpp:member:`cap_edge <mcpwm_capture_event_data_t::cap_edge>` seen in the callback may not match the physical GPIO edge.
|
||||
- Adjacent opposite-edge gaps are **not pulse width**, and **the true duty cycle cannot be recovered** from them.
|
||||
|
||||
Always compute period or frequency from timestamps of the same reported edge type.
|
||||
|
||||
.. note::
|
||||
|
||||
Keep ``prescale = 1`` and capture both edges when measuring pulse width or duty cycle. Raise ``prescale`` only when you need to reduce the capture rate for fast inputs and you only care about period or frequency.
|
||||
|
||||
The figures below show how ``prescale`` affects capture timing for rising-only, falling-only, and both-edge modes.
|
||||
|
||||
.. figure:: /../_static/mcpwm/capture_prescale_rising.svg
|
||||
:align: center
|
||||
:alt: Rising-edge only capture with prescale bypass and prescale 4.
|
||||
|
||||
Rising-edge only. With ``prescale = 1`` every rising edge captures as ``R``. With ``prescale > 1``, the first capture is at cycle ``prescale / 2 - 1``, then every ``prescale``-th rising edge.
|
||||
|
||||
.. figure:: /../_static/mcpwm/capture_prescale_falling.svg
|
||||
:align: center
|
||||
:alt: Falling-edge only capture with prescale bypass and prescale 4.
|
||||
|
||||
Falling-edge only. With ``prescale = 1`` every falling edge captures as ``F``. With ``prescale > 1``, GPIO falling edges do not directly produce captures; events land on rising steps while ``cap_edge`` still reports ``F``.
|
||||
|
||||
.. figure:: /../_static/mcpwm/capture_prescale_both.svg
|
||||
:align: center
|
||||
:alt: Both-edge capture with prescale bypass and prescale 4.
|
||||
|
||||
Both-edge capture. With ``prescale = 1``, ``R``/``F`` match the physical pin edges. With ``prescale > 1``, captures fire on rising pin steps only, while reported ``R``/``F`` alternate after prescaling.
|
||||
|
||||
.. warning::
|
||||
|
||||
Do not infer the physical GPIO transition from :cpp:member:`mcpwm_capture_event_data_t::cap_edge` when ``prescale > 1``, and do not treat adjacent opposite-edge gaps as pulse width.
|
||||
|
||||
Enable and Disable Capture Channel
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
|
||||
@@ -936,6 +936,49 @@ MCPWM 捕获通道支持在信号上检测到有效边沿时发送通知。须
|
||||
|
||||
此函数会延迟安装 MCPWM 捕获的中断服务。中断服务只能通过 :cpp:type:`mcpwm_del_capture_channel` 移除。
|
||||
|
||||
输入预分频
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
捕获通道内部按**固定顺序**串行处理输入：
|
||||
|
||||
1. 先用 ``prescale`` 对 GPIO 波形做分频（``0`` 或 ``1`` 表示 bypass）；
|
||||
2. 再根据 ``pos_edge``/``neg_edge`` 决定哪些分频后的事件上报给软件。
|
||||
|
||||
因此，硬件并不是先按物理 GPIO 边沿极性过滤，再对这些边沿做分频。对于 ``prescale > 1``：
|
||||
|
||||
- 回调里看到的 :cpp:member:`cap_edge <mcpwm_capture_event_data_t::cap_edge>` 可能和 GPIO 的真实物理边沿不一致。
|
||||
- 相邻异沿之间的时间差**不代表脉宽**，并且**无法据此还原真实占空比**。
|
||||
|
||||
计算周期或频率时，请始终使用相同上报边沿类型（同沿）的两次时间戳。
|
||||
|
||||
.. note::
|
||||
|
||||
测量脉宽或占空比时，请保持 ``prescale = 1`` 并同时捕获双边沿。只有在输入过快、你只关心周期或频率时，才建议提高 ``prescale`` 来降低捕获速率。
|
||||
|
||||
下图说明 ``prescale`` 对仅上升沿、仅下降沿和双边沿捕获时序的影响。
|
||||
|
||||
.. figure:: /../_static/mcpwm/capture_prescale_rising.svg
|
||||
:align: center
|
||||
:alt: 仅上升沿捕获：prescale bypass 与 prescale 4。
|
||||
|
||||
仅上升沿。``prescale = 1`` 时，每个上升沿都会捕获为 ``R``。``prescale > 1`` 时，首次捕获出现在 cycle ``prescale / 2 - 1``，之后每隔 ``prescale`` 个上升沿捕获一次。
|
||||
|
||||
.. figure:: /../_static/mcpwm/capture_prescale_falling.svg
|
||||
:align: center
|
||||
:alt: 仅下降沿捕获：prescale bypass 与 prescale 4。
|
||||
|
||||
仅下降沿。``prescale = 1`` 时，每个下降沿都会捕获为 ``F``。``prescale > 1`` 时，GPIO 的下降沿不会直接触发捕获；事件会落在上升沿步骤上，但 ``cap_edge`` 仍然上报 ``F``。
|
||||
|
||||
.. figure:: /../_static/mcpwm/capture_prescale_both.svg
|
||||
:align: center
|
||||
:alt: 双边沿捕获：prescale bypass 与 prescale 4。
|
||||
|
||||
双边沿。``prescale = 1`` 时，``R``/``F`` 与引脚真实边沿一致。``prescale > 1`` 时，捕获只会落在上升沿步骤上，而分频后的上报事件在 ``R``/``F`` 之间交替。
|
||||
|
||||
.. warning::
|
||||
|
||||
当 ``prescale > 1`` 时，不要根据 :cpp:member:`mcpwm_capture_event_data_t::cap_edge` 去推断 GPIO 的真实跳变方向，也不要把相邻异沿间隔当作脉宽。
|
||||
|
||||
启用或禁用捕获通道
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
|
||||
Reference in New Issue
Block a user