arch/sim: don't block on the wrapped RX segment of the simulated UART - #20028
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raiden00pl wants to merge 2 commits into
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arch/sim: don't block on the wrapped RX segment of the simulated UART#20028raiden00pl wants to merge 2 commits into
raiden00pl wants to merge 2 commits into
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The console fd is blocking (host_uart_start() never sets O_NONBLOCK), so when a burst of input ends exactly at the wrap boundary of the RX circular buffer, the second host_uart_gets() in tty_dmareceive() blocks inside the timer callback and freezes the whole simulator until the host sends another byte. Poll the fd first so the wrapped segment is only read when data is really available. Assisted-by: Claude Code Signed-off-by: raiden00pl <raiden00@railab.me>
raiden00pl
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xiaoxiang781216
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September 1, 2026 08:01
fix nxstyle errors Signed-off-by: raiden00pl <raiden00@railab.me>
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jerpelea
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Sep 1, 2026
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| xfer->nbytes = ret; | ||
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| if (ret == xfer->length && xfer->nlength > 0) | ||
| /* The console fd is blocking, so only continue into the wrapped |
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should we change fd to the non-blocking mode
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Summary
The console fd is blocking (host_uart_start() never sets O_NONBLOCK), so when a burst of input ends exactly at the wrap boundary of the RX circular buffer, the second host_uart_gets() in tty_dmareceive() blocks inside the timer callback and freezes the whole simulator until the host sends another byte. Poll the fd first so the wrapped segment is only read when data is really available.
Impact
we can remove workaround in NTFC for sim:
https://github.com/apache/nuttx-ntfc/blob/f68efe4e6080c0fa7018664cd284789d3314cf55/src/ntfc/device/sim.py#L38-L39
Testing
Simulator works on NTFC without workaround from above