dif_uart.h

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// Copyright lowRISC contributors.
// Licensed under the Apache License, Version 2.0, see LICENSE for details.
// SPDX-License-Identifier: Apache-2.0

#ifndef OPENTITAN_SW_DEVICE_LIB_DIF_DIF_UART_H_
#define OPENTITAN_SW_DEVICE_LIB_DIF_DIF_UART_H_

/**
 * @file
 * @brief <a href="/hw/ip/uart/doc/">UART</a> Device Interface Functions
 */

#include <stdint.h>

#include "sw/device/lib/base/mmio.h"
#include "sw/device/lib/dif/dif_warn_unused_result.h"

// Header Extern Guard (so header can be used from C and C++)
#ifdef __cplusplus
extern "C" {
#endif  // __cplusplus

/**
 * A toggle state: enabled, or disabled.
 *
 * This enum may be used instead of a `bool` when describing an enabled/disabled
 * state.
 */
typedef enum dif_uart_toggle {
  /**
   * The "enabled" state.
   */
  kDifUartToggleEnabled,
  /**
   * The "disabled" state.
   */
  kDifUartToggleDisabled,
} dif_uart_toggle_t;

/**
 * A parity state: odd, or even.
 */
typedef enum dif_uart_parity {
  /**
   * Indicates the "odd" parity.
   */
  kDifUartParityOdd = 0,
  /**
   * Indicates the "even" parity.
   */
  kDifUartParityEven,
} dif_uart_parity_t;

/**
 * Hardware instantiation parameters for UART.
 *
 * This struct describes information about the underlying hardware that is
 * not determined until the hardware design is used as part of a top-level
 * design.
 */
typedef struct dif_uart_params {
  /**
   * The base address for the UART hardware registers.
   */
  mmio_region_t base_addr;
} dif_uart_params_t;

/**
 * Runtime configuration for UART.
 *
 * This struct describes runtime information for one-time configuration of the
 * hardware.
 */
typedef struct dif_uart_config {
  /**
   * The UART baudrate.
   */
  uint32_t baudrate;
  /**
   * The frequency of the clock driving the UART.
   */
  uint32_t clk_freq_hz;
  /**
   * Whether to enable parity checking.
   */
  dif_uart_toggle_t parity_enable;
  /**
   * The parity to set.
   */
  dif_uart_parity_t parity;
} dif_uart_config_t;

/**
 * A handle to UART.
 *
 * This type should be treated as opaque by users.
 */
typedef struct dif_uart { dif_uart_params_t params; } dif_uart_t;

/**
 * The result of a UART operation.
 */
typedef enum dif_uart_result {
  /**
   * Indicates that the operation succeeded.
   */
  kDifUartOk = 0,
  /**
   * Indicates some unspecified failure.
   */
  kDifUartError = 1,
  /**
   * Indicates that some parameter passed into a function failed a
   * precondition.
   *
   * When this value is returned, no hardware operations occured.
   */
  kDifUartBadArg = 2,
} dif_uart_result_t;

/**
 * The result of a UART operation.
 */
typedef enum dif_uart_config_result {
  /**
   * Indicates that the operation succeeded.
   */
  kDifUartConfigOk = kDifUartOk,
  /**
   * Indicates some unspecified failure.
   */
  kDifUartConfigError = kDifUartError,
  /**
   * Indicates that some parameter passed into a function failed a
   * precondition.
   *
   * When this value is returned, no hardware operations occured.
   */
  kDifUartConfigBadArg = kDifUartBadArg,
  /**
   * Indicates that the given configuration parameters are not valid.
   */
  kDifUartConfigBadConfig,
  /**
   * Indicates that the calculated NCO value was not valid.
   */
  kDifUartConfigBadNco,
} dif_uart_config_result_t;

/**
 * A UART interrupt request type.
 */
typedef enum dif_uart_irq {
  /**
   * Fired when the TX FIFO dips below its watermark.
   */
  kDifUartIrqTxWatermark = 0,
  /**
   * Fired when the RX FIFO goes over its watermark.
   */
  kDifUartIrqRxWatermark,
  /**
   * Fired when the TX FIFO is empty.
   */
  kDifUartIrqTxEmpty,
  /**
   * Fired when the RX FIFO overflows.
   */
  kDifUartIrqRxOverflow,
  /**
   * Fired when an RX framing error occurs.
   */
  kDifUartIrqRxFrameErr,
  /**
   * Fired to indicate an RX break condition.
   */
  kDifUartIrqRxBreakErr,
  /**
   * Fired when the RX FIFO timeout expires before it is emptied.
   */
  kDifUartIrqRxTimeout,
  /**
   * Fired when an RX parity error is detected.
   */
  kDifUartIrqRxParityErr,
} dif_uart_irq_t;

/**
 * A snapshot of the enablement state of the interrupts for UART.
 *
 * This is an opaque type, to be used with the `dif_uart_irq_disable_all()` and
 * `dif_uart_irq_restore_all()` functions.
 */
typedef uint32_t dif_uart_irq_snapshot_t;

/**
 * A UART FIFO watermark depth configuration.
 */
typedef enum dif_uart_watermark {
  /**
   * Indicates a one-byte watermark.
   */
  kDifUartWatermarkByte1 = 0,
  /**
   * Indicates a four-byte watermark.
   */
  kDifUartWatermarkByte4,
  /**
   * Indicates an eight-byte watermark.
   */
  kDifUartWatermarkByte8,
  /**
   * Indicates a sixteen-byte watermark.
   */
  kDifUartWatermarkByte16,
  /**
   * Indicates a thirty-byte watermark.
   */
  kDifUartWatermarkByte30,
} dif_uart_watermark_t;

/**
 * A UART FIFO reset selection.
 */
typedef enum dif_uart_fifo_reset {
  /**
   * Indicates that the RX FIFO should be reset.
   */
  kDifUartFifoResetRx = 0,
  /**
   * Indicates that the TX FIFO should be reset.
   */
  kDifUartFifoResetTx,
  /**
   * Indicates that both FIFOs should be reset.
   */
  kDifUartFifoResetAll,
} dif_uart_fifo_reset_t;

/**
 * A UART system/line loopback configuration.
 */
typedef enum dif_uart_loopback {
  /**
   * Indicates that outgoing TX bits should be recieved through RX.
   */
  kDifUartLoopbackSystem = 0,
  /**
   * Indicates that incoming RX bits should be forwarded to TX.
   */
  kDifUartLoopbackLine,
} dif_uart_loopback_t;

/**
 * The size of the UART TX and RX FIFOs, in bytes.
 */
extern const uint32_t kDifUartFifoSizeBytes;

/**
 * Creates a new handle for UART.
 *
 * This function does not actuate the hardware.
 *
 * @param params Hardware instantiation parameters.
 * @param uart Out param for the initialized handle.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_init(dif_uart_params_t params, dif_uart_t *uart);

/**
 * Configures UART with runtime information.
 *
 * This function should need to be called once for the lifetime of `handle`.
 *
 * @param uart A UART handle.
 * @param config Runtime configuration parameters.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_config_result_t dif_uart_configure(const dif_uart_t *uart,
                                            dif_uart_config_t config);

/**
 * Returns whether a particular interrupt is currently pending.
 *
 * @param uart A UART handle.
 * @param irq An interrupt type.
 * @param is_pending Out-param for whether the interrupt is pending.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_is_pending(const dif_uart_t *uart,
                                          dif_uart_irq_t irq, bool *is_pending);

/**
 * Acknowledges a particular interrupt, indicating to the hardware that it has
 * been successfully serviced.
 *
 * @param uart A UART handle.
 * @param irq An interrupt type.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_acknowledge(const dif_uart_t *uart,
                                           dif_uart_irq_t irq);

/**
 * Checks whether a particular interrupt is currently enabled or disabled.
 *
 * @param uart A UART handle.
 * @param irq An interrupt type.
 * @param state Out-param toggle state of the interrupt.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_get_enabled(const dif_uart_t *uart,
                                           dif_uart_irq_t irq,
                                           dif_uart_toggle_t *state);

/**
 * Sets whether a particular interrupt is currently enabled or disabled.
 *
 * @param uart A UART handle.
 * @param irq An interrupt type.
 * @param state The new toggle state for the interrupt.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_set_enabled(const dif_uart_t *uart,
                                           dif_uart_irq_t irq,
                                           dif_uart_toggle_t state);

/**
 * Forces a particular interrupt, causing it to be serviced as if hardware had
 * asserted it.
 *
 * @param uart A UART handle.
 * @param irq An interrupt type.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_force(const dif_uart_t *uart,
                                     dif_uart_irq_t irq);

/**
 * Disables all interrupts, optionally snapshotting all toggle state for later
 * restoration.
 *
 * @param uart A UART handle.
 * @param snapshot Out-param for the snapshot; may be `NULL`.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_disable_all(const dif_uart_t *uart,
                                           dif_uart_irq_snapshot_t *snapshot);

/**
 * Restores interrupts from the given snapshot.
 *
 * This function can be used with `dif_uart_irq_disable_all()` to temporary
 * interrupt save-and-restore.
 *
 * @param uart A UART handle.
 * @param snapshot A snapshot to restore from.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_irq_restore_all(
    const dif_uart_t *uart, const dif_uart_irq_snapshot_t *snapshot);

/**
 * Sets the RX FIFO watermark.
 *
 * This function is only useful when the corresponding interrupt is enabled.
 * When the queued RX FIFO number of bytes rises to or above this
 * level, the RX watermark interrupt is raised.
 *
 * @param uart A UART handle.
 * @param watermark RX FIFO watermark.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_watermark_rx_set(const dif_uart_t *uart,
                                            dif_uart_watermark_t watermark);

/**
 * Sets the TX FIFO watermark.
 *
 * This function is only useful when the corresponding interrupt is enabled.
 * When the queued RX FIFO number of bytes rises to or above this
 * level, the RX watermark interrupt is raised.
 *
 * @param uart A UART handle.
 * @param watermark TX FIFO watermark.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_watermark_tx_set(const dif_uart_t *uart,
                                            dif_uart_watermark_t watermark);

/**
 * Sends bytes over UART.
 *
 * Can be used from inside an UART ISR.
 *
 * This function attempts to write `bytes_requested` number of bytes to the
 * UART TX FIFO from `bytes_requested`, and passes `bytes_written` back to
 * the caller. `bytes_written` is optional, NULL should be passed in if the
 * value is not needed.
 *
 * @param uart A UART handle.
 * @param data Data to be written.
 * @param bytes_requested Number of bytes requested to be written by the caller.
 * @param[out] bytes_written Number of bytes written (optional).
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_bytes_send(const dif_uart_t *uart,
                                      const uint8_t *data,
                                      size_t bytes_requested,
                                      size_t *bytes_written);

/**
 * Recieves bytes over UART.
 *
 * Can be used from inside an UART ISR.
 *
 * This function attempts to read `bytes_requested` number of bytes from the
 * UART RX FIFO into `data`, and passes `bytes_read` back to the caller.
 * `bytes_read` is optional, NULL should be passed in if the value is not
 * needed.
 *
 * @param uart A UART handle.
 * @param bytes_requested Number of bytes requested to be read by the caller.
 * @param[out] data Buffer for up to `bytes_requested` bytes of read data.
 * @param[out] bytes_read Number of bytes read (optional).
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_bytes_receive(const dif_uart_t *uart,
                                         size_t bytes_requested, uint8_t *data,
                                         size_t *bytes_read);

/**
 * Transmits a single UART byte (polled).
 *
 * This operation is polled, and will busy wait until a byte has been sent.
 *
 * Must not be used inside an ISR.
 *
 * @param uart A UART handle.
 * @param byte Byte to be transmitted.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_byte_send_polled(const dif_uart_t *uart,
                                            uint8_t byte);

/**
 * Receives a single UART byte (polled).
 *
 * This operation is polled, and will busy wait until a byte has been read.
 *
 * Must not be used inside an ISR.
 *
 * @param uart A UART handle.
 * @param[out] byte Received byte.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_byte_receive_polled(const dif_uart_t *uart,
                                               uint8_t *byte);

/**
 * Gets the number of bytes available to be read from the UART RX FIFO.
 *
 * This function can be used to check FIFO full and empty conditions.
 *
 * @param uart A UART handle.
 * @param[out] num_bytes Number of bytes available to be read.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_rx_bytes_available(const dif_uart_t *uart,
                                              size_t *num_bytes);

/**
 * Gets the number of bytes available to be written from the UART TX FIFO.
 *
 * This function can be used to check FIFO full and empty conditions.
 *
 * @param uart A UART handle.
 * @param[out] num_bytes Number of bytes available to be written.
 * @return The result of the operation.
 */
DIF_WARN_UNUSED_RESULT
dif_uart_result_t dif_uart_tx_bytes_available(const dif_uart_t *uart,
                                              size_t *num_bytes);
/**
 * UART TX reset RX/TX FIFO.
 *
 * Reset both FIFOs, or the requested one.
 *
 * @param uart A UART handle.
 * @param reset FIFO to reset (RX or TX).
 * @return The result of the operation.
 */
dif_uart_result_t dif_uart_fifo_reset(const dif_uart_t *uart,
                                      dif_uart_fifo_reset_t reset);

/**
 * Enables or disables a transmit/receive loopback.
 *
 * This API can be used for testing, such as to validate transmit and receive
 * routines.
 *
 * Loopback should only be enabled when device is in the IDLE state to prevent
 * data loss/coruption. Behaviour depends on the `loopback` parameter:
 *    - `kDifUartLoopbackSystem`:
 *      Receives the data that is being transmitted. No external data can be
 *      received (from the RX line). When enabled the TX line goes high.
 *    - `kDifUartLoopbackLine`:
 *      Transmits the data that is being received. No internal data can be
 *      sent out (from the TX FIFO). When enabled the RX line goes high.
 *
 * @param uart A UART handle.
 * @param loopback Loopback type (transmit/receive).
 * @param enable Enable/disable control flag.
 * @return The result of the operation.
 */
dif_uart_result_t dif_uart_loopback_set(const dif_uart_t *uart,
                                        dif_uart_loopback_t loopback,
                                        dif_uart_toggle_t enable);

#ifdef __cplusplus
}  // extern "C"
#endif  // __cplusplus

#endif  // OPENTITAN_SW_DEVICE_LIB_DIF_DIF_UART_H_