nRF52 UARTE EasyDMA TX — unmodified Zephyr console boots in the sim#340
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The Nrf52Uarte model tracked registers but TASKS_STARTTX did nothing — no DMA read of the TXD buffer, no output, no completion events. nRF drivers (nrfx/Zephyr) drive the console exclusively through UARTE EasyDMA, so the console was silent and a polling `poll_out` hung forever waiting on EVENTS_TXSTOPPED. Implement EasyDMA TX via the existing needs_bus_tick/tick_with_bus pattern (the RADIO PACKETPTR precedent): on STARTTX, DMA-read TXD.MAXCNT bytes from TXD.PTR, emit them to stdout + the capture sink, set TXD.AMOUNT, and raise the begin→drain→stop events (TXSTARTED/TXDRDY/ENDTX/TXSTOPPED) the driver polls — nrfx enables the ENDTX_STOPTX short and waits on TXSTOPPED. - Point nrf52840 uart0 at the EasyDMA model (it is a UARTE in silicon; the legacy `"uart"` mapping was the inaccuracy), irq 2. - Wire Bus::attach_uart_tx_sink to capture/echo the UARTE console. - Add an EasyDMA TX regression test. Result: unmodified Zephyr v3.7 hello_world boots and prints "Hello World! nrf52840dk/nrf52840" in the sim, both via the top-level run and `labwired test` (uart_contains assertion).
The UARTE model gained an EasyDMA TX path so an unmodified nrfx/Zephyr console boots under the sim. That changes a peripheral model after the 2026-06-17 silicon capture, which the drift gate flags. Record a dated drift_ack on nrf52840 and the Seeed XIAO (same silicon), and regenerate VALIDATION_STATUS.md. Additive change; the prior register sweep holds and a UARTE TX live diff stays tracked.
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What
Implements nRF52 UARTE EasyDMA TX so unmodified Zephyr (and any nrfx-based) firmware can use the console.
Nrf52Uartepreviously tracked registers butTASKS_STARTTXdid nothing — no DMA read of the TXD buffer, no output, no completion events. Since nrfx/Zephyr drive the console exclusively through UARTE EasyDMA, the console was silent and a pollingpoll_outhung forever onEVENTS_TXSTOPPED.Changes
Nrf52Uartevia the existingneeds_bus_tick/tick_with_buspattern (the RADIO PACKETPTR precedent): on STARTTX, DMA-readTXD.MAXCNTbytes fromTXD.PTR, emit to stdout + capture sink, setTXD.AMOUNT, and raise the begin→drain→stop events (TXSTARTED/TXDRDY/ENDTX/TXSTOPPED). nrfx enables theENDTX_STOPTXshort and waits onTXSTOPPED, so that one must fire.nrf52840uart0 at the EasyDMA model (nrf52840_uart, irq 2) — it is a UARTE in silicon; the legacy"uart"mapping was the inaccuracy.Bus::attach_uart_tx_sinkto capture/echo the UARTE console.Verification
Unmodified Zephyr v3.7.2 LTS
samples/hello_world(built gnuarmemb, no SDK) boots and prints:both via the top-level run and
labwired test --script(uart_containsassertion → exit 0). Full nRF52 + UARTE test suites pass; no regressions.This is Phase 0 of a broader Zephyr integration (west runner + hosted Zephyr build to follow). The SCB
SYSRESETREQwarm-reset that Zephyr'sSystemInitneeds is already onmain; this PR is the remaining console piece.