[PATCH] bsps/xilinx-zynqmp: Avoid constant UART reinit

[Kinsey Moore]

I only settled on ' ' because it was already being used and clearly brought the UART back into a fully operational state. I'll take a look at other characters to see what else might work.

Kinsey

-----Original Message-----
From: Gedare Bloom <gedare at rtems.org> 
Sent: Monday, April 12, 2021 13:49
To: Kinsey Moore <kinsey.moore at oarcorp.com>
Cc: devel at rtems.org
Subject: Re: [PATCH] bsps/xilinx-zynqmp: Avoid constant UART reinit

am curious, are there any non-printable character that can be used to kick it?

On Fri, Apr 9, 2021 at 4:35 PM Kinsey Moore <kinsey.moore at oarcorp.com> wrote:
>
> Constantly reinitializing the Cadence UART on every character output
> causes data corruption/loss on some ZynqMP hardware. Only initialize
> the UART once for early output and give it a kick on startup.
> ---
>  bsps/aarch64/xilinx-zynqmp/console/console.c | 6 ++++++
>  bsps/shared/dev/serial/zynq-uart-polled.c    | 9 ++++++---
>  2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/bsps/aarch64/xilinx-zynqmp/console/console.c b/bsps/aarch64/xilinx-zynqmp/console/console.c
> index 84e158d3f6..8b12d59d4c 100644
> --- a/bsps/aarch64/xilinx-zynqmp/console/console.c
> +++ b/bsps/aarch64/xilinx-zynqmp/console/console.c
> @@ -112,6 +112,12 @@ static void zynqmp_debug_console_early_init(char c)
>      &zynqmp_uart_instances[BSP_CONSOLE_MINOR].base;
>
>    zynq_uart_initialize(base);
> +  BSP_output_char = zynqmp_debug_console_out;
> +  /*
> +   * Some ZynqMP UARTs have a hardware bug that causes TX/RX logic restarts to
> +   * require a kick after baud rate registers are initialized.
> +   */
> +  zynqmp_debug_console_out(' ');
>    zynqmp_debug_console_out(c);
>  }
>
> diff --git a/bsps/shared/dev/serial/zynq-uart-polled.c b/bsps/shared/dev/serial/zynq-uart-polled.c
> index 442431d502..74e7255ec2 100644
> --- a/bsps/shared/dev/serial/zynq-uart-polled.c
> +++ b/bsps/shared/dev/serial/zynq-uart-polled.c
> @@ -128,14 +128,17 @@ void zynq_uart_initialize(rtems_termios_device_context *base)
>
>    regs->control &= ~(ZYNQ_UART_CONTROL_RXEN | ZYNQ_UART_CONTROL_TXEN);
>    regs->control = ZYNQ_UART_CONTROL_RXDIS
> -    | ZYNQ_UART_CONTROL_TXDIS
> -    | ZYNQ_UART_CONTROL_RXRES
> -    | ZYNQ_UART_CONTROL_TXRES;
> +    | ZYNQ_UART_CONTROL_TXDIS;
>    regs->mode = ZYNQ_UART_MODE_CHMODE(ZYNQ_UART_MODE_CHMODE_NORMAL)
>      | ZYNQ_UART_MODE_PAR(ZYNQ_UART_MODE_PAR_NONE)
>      | ZYNQ_UART_MODE_CHRL(ZYNQ_UART_MODE_CHRL_8);
>    regs->baud_rate_gen = ZYNQ_UART_BAUD_RATE_GEN_CD(brgr);
>    regs->baud_rate_div = ZYNQ_UART_BAUD_RATE_DIV_BDIV(bauddiv);
> +  /* A Tx/Rx logic reset must be issued after baud rate manipulation */
> +  regs->control = ZYNQ_UART_CONTROL_RXDIS
> +    | ZYNQ_UART_CONTROL_TXDIS
> +    | ZYNQ_UART_CONTROL_RXRES
> +    | ZYNQ_UART_CONTROL_TXRES;
>    regs->rx_fifo_trg_lvl = ZYNQ_UART_RX_FIFO_TRG_LVL_RTRIG(0);
>    regs->rx_timeout = ZYNQ_UART_RX_TIMEOUT_RTO(0);
>    regs->control = ZYNQ_UART_CONTROL_RXEN
> --
> 2.20.1
>
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