rp2: use irq_add_shared_handler() for DMA_IRQ_0 instead of fixed isr_dma_0()#11054
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…dma_0() audio_dma.c defined the DMA_IRQ_0 handler as the fixed isr_dma_0() linker symbol and dispatched to both audio and rp2pio from it. Per the Pico SDK docs this is impolite: it permanently owns the vector and prevents other code from cooperating on the IRQ at runtime. It also meant rp2pio's DMA completion was silently broken when CIRCUITPY_AUDIOCORE=0, since the dispatch lived inside that guard. Convert DMA_IRQ_0 to per-subsystem shared handlers: audiocore and rp2pio each register their own handler with irq_add_shared_handler(), add it on the first channel they enable and remove it on the last, and acknowledge only their own channels. picodvi's exclusive DMA_IRQ_1 handler is unchanged. Document the DMA IRQ allocation policy (which IRQs are shared vs. exclusive) in common-hal/microcontroller/__init__.c. Adds manual hardware regression tests under tests/circuitpython-manual/rp2pio/ that exercise audio DMA, rp2pio background write, and rp2pio background read sharing DMA_IRQ_0. They use only pre-existing public APIs and pass identically before and after this change. Closes adafruit#9992 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Looks good to me. Thanks for the fix!
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This post was mostly written by Claude Code. I originally addressed this bug using Copilot, which was using ChatGPT-4.5, but Claude did a much better job. Copilot's own tests would not run. The Claude code is cleaner as well. -- @dhalbert
Addresses #9992.
Problem
ports/raspberrypi/audio_dma.cdefined the DMA_IRQ_0 handler as the fixedisr_dma_0()linker symbol and dispatched to both audio and rp2pio from it. Per the Pico SDK docs, definingisr_dma_0makes that function the permanent DMA_IRQ_0 vector and prevents other code from cooperating on the IRQ at runtime ("can cause link conflicts at runtime, and offers no runtime performance benefit"). See also the discussion in #9868.Two concrete issues:
#if CIRCUITPY_AUDIOCORE, yet rp2pio relied on it — so rp2pio background DMA was silently broken whenCIRCUITPY_AUDIOCORE=0.Change
Convert DMA_IRQ_0 to per-subsystem shared handlers:
audio_dma.c) and rp2pio (StateMachine.c) each register their own handler viairq_add_shared_handler(), add it on the first channel they enable and remove it on the last, and acknowledge only their own channels.dma_hw->inte0/irq_set_mask_enabled()manipulation is replaced withdma_irqn_set_channel_enabled()/irq_set_enabled().DMA_IRQ_1handler is unchanged.common-hal/microcontroller/__init__.c.This also fixes the
CIRCUITPY_AUDIOCORE=0case, since rp2pio now owns its own handler.Testing
Builds clean for RP2040 (
raspberry_pi_pico_w) and RP2350 (raspberry_pi_pico2).Adds manual hardware regression tests under
tests/circuitpython-manual/rp2pio/that exercise audio DMA, rp2pio background write, and rp2pio background read sharing DMA_IRQ_0. They use only pre-existing public APIs and pass identically on firmware built before and after this change (verified on hardware).I tested using the regressions tests listed above, and also tested on Fruit Jam using a hacked-up version of the Fruit Jam OS startup animation program. I made it repeat over and over, and also added some NeoPixel manipulations. It worked. -- @dhalbert
🤖 Generated with Claude Code