In the lower half UART driver for PIC32MZ architecture, adding the
TIOCxBRK ioctl calls, which allow an application to transmit a UART
line BREAK signal.
This architecture does not support BSD-style BREAK in hardware so our
implementation follows the precedent set in STM32, GD32, and Kinetis
architectures: By default, if only PIC32MZ_UART_BREAKS is configured,
we produce the hardware-native BREAK, which lasts for 12 bit lengths;
if, in addition, PIC32MZ_SERIALBRK_BSDCOMPAT is configured, we
generate a BSD-style BREAK by putting the TX pin in GPIO mode and
driving it low "manually" until told to stop.
* arch/mips/src/pic32mz/Kconfig
(config PIC32MZ_UART_BREAKS): New. Appears as
CONFIG_PIC32MZ_UART_BREAKS in code.
(config PIC32MZ_SERIALBRK_BSDCOMPAT): New. Appears as
CONFIG_PIC32MZ_SERIALBRK_BSDCOMPAT in code.
* arch/mips/src/pic32mz/hardware/pic32mz_pps.h
(__PPS_OUTPUT_REGADDR_TO_GPIO, PPS_OUTPUT_REGADDR_TO_GPIO): New
macros to automatically determine the GPIO port and pin from the
corresponding PPS (Peripheral Pin Select) define. Since there is a
one-to-one correspondence between PPS output mappings and a single
port and pin, these macros avoid writing redundant pin mappings. We
use this when switching the TX pin from UART to GPIO to generate
the BREAK and we could use it in other peripheral drivers in the
future to override hardware behavior.
* arch/mips/src/pic32mz/pic32mz_serial.c
(struct up_dev_s): Add new field 'brk' to indicate line break in
progress when built with PIC32MZ_UART_BREAKS. If generating BSD-
compatible BREAKs, also add tx_gpio, tx_pps_reg, and tx_pps_val, to
let us toggle the pin between UART and GPIO modes.
(up_ioctl): Add cases for TIOCSBRK and TIOCCBRK to turn BREAK on and
off, with both hardware-native and BSD-compatible implementations.
This is similar to the STM32F7 implementation.
(up_txint): Block enabling TX interrupt if line break in progress.
This is similar to the STM32F7 implementation.
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