drivers/periph/uart: add periph_uart_tx_ondemand feature#20108
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benpicco merged 4 commits intoRIOT-OS:masterfrom Dec 14, 2023
Merged
drivers/periph/uart: add periph_uart_tx_ondemand feature#20108benpicco merged 4 commits intoRIOT-OS:masterfrom
benpicco merged 4 commits intoRIOT-OS:masterfrom
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Platform: ARM
benpicco
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Nov 24, 2023
| #ifndef SOFT_UART_PARAMS_H | ||
| #define SOFT_UART_PARAMS_H | ||
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| #include "board.h" |
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This is not exactly related to this PR, but without it SOFT_UART_PARAM_xx set in board.h would not get applied.
I first thought of using the software UART to invert the line polarity, but then I found I can use a real UART instead if I re-configure the TX pin.
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Contribution description
We have a one-wire bus where the idle level is LOW:
If two sensors pull the bus high at the same time, no-one will be able to send anything.
To make this work with standard UART where idle is LOW, we employ a little hack in which we de-mux the UART TX pin when we are not sending and only mux it to TX when we want to send a frame.
This generates a spurious 0 byte after the de-muxing, but since our DOSE frames are well delimited, this noise outside the frame is no issue.
Testing procedure
This bus is really slow (2400 Baud) but it works:
Issues/PRs references
previous attempt at this was #14300