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On Raspberry Pi 4 and earlier models the firmware provides a low speed (up to 115200 baud) bit-bashed UART on arbitrary GPIOs using the second VPU core. The firmware driver is designed to support 19200 baud. Higher rates up to 115200 seem to work but there may be more jitter. This can be useful for debug or managing additional low speed peripherals if the hardware PL011 and 8250 hardware UARTs are already used for console / bluetooth. The firmware driver requires a fixed core clock frequency and also requires the VPU PWM audio driver to be disabled (dtparam=audio=off) Runtime configuration is handled via the vc-mailbox APIs with the FIFO buffers being allocated in uncached VPU addressable memory. The FIFO pointers are stored in spare VideoCore multi-core sync registers in order to reduce the number of uncached SDRAM accesses thereby reducing jitter. Signed-off-by: Tim Gover <tim.gover@raspberrypi.com> serial: rpi-fw-uart: Demote debug log messages A dev_info call in rpi_fw_uart_configure causes kernel log output every time one opens the UART. Demote it to dev_dbg. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Linux kernel
There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first.
In order to build the documentation, use make htmldocs or
make pdfdocs. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.
Build status for rpi-6.1.y:
Build status for rpi-6.6.y:
Build status for rpi-6.12.y:
