uart.h

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#ifndef _IPXE_UART_H
#define _IPXE_UART_H

/** @file
 *
 * 16550-compatible UART
 *
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <stdint.h>

/** Transmitter holding register */
#define UART_THR 0x00

/** Receiver buffer register */
#define UART_RBR 0x00

/** Interrupt enable register */
#define UART_IER 0x01

/** FIFO control register */
#define UART_FCR 0x02
#define UART_FCR_FE     0x01    /**< FIFO enable */

/** Line control register */
#define UART_LCR 0x03
#define UART_LCR_WLS0   0x01    /**< Word length select bit 0 */
#define UART_LCR_WLS1   0x02    /**< Word length select bit 1 */
#define UART_LCR_STB    0x04    /**< Number of stop bits */
#define UART_LCR_PEN    0x08    /**< Parity enable */
#define UART_LCR_EPS    0x10    /**< Even parity select */
#define UART_LCR_DLAB   0x80    /**< Divisor latch access bit */

#define UART_LCR_WORD_LEN(x)    ( ( (x) - 5 ) << 0 )    /**< Word length */
#define UART_LCR_STOP_BITS(x)   ( ( (x) - 1 ) << 2 )    /**< Stop bits */
#define UART_LCR_PARITY(x)      ( ( (x) - 0 ) << 3 )    /**< Parity */

/**
 * Calculate line control register value
 *
 * @v word_len          Word length (5-8)
 * @v parity            Parity (0=none, 1=odd, 3=even)
 * @v stop_bits         Stop bits (1-2)
 * @ret lcr             Line control register value
 */
#define UART_LCR_WPS( word_len, parity, stop_bits )     \
        ( UART_LCR_WORD_LEN ( (word_len) ) |            \
          UART_LCR_PARITY ( (parity) ) |                \
          UART_LCR_STOP_BITS ( (stop_bits) ) )

/** Default LCR value: 8 data bits, no parity, one stop bit */
#define UART_LCR_8N1 UART_LCR_WPS ( 8, 0, 1 )

/** Modem control register */
#define UART_MCR 0x04
#define UART_MCR_DTR    0x01    /**< Data terminal ready */
#define UART_MCR_RTS    0x02    /**< Request to send */

/** Line status register */
#define UART_LSR 0x05
#define UART_LSR_DR     0x01    /**< Data ready */
#define UART_LSR_THRE   0x20    /**< Transmitter holding register empty */
#define UART_LSR_TEMT   0x40    /**< Transmitter empty */

/** Scratch register */
#define UART_SCR 0x07

/** Divisor latch (least significant byte) */
#define UART_DLL 0x00

/** Divisor latch (most significant byte) */
#define UART_DLM 0x01

/** Maximum baud rate */
#define UART_MAX_BAUD 115200

/** A 16550-compatible UART */
struct uart {
        /** I/O port base address */
        void *base;
        /** Baud rate divisor */
        uint16_t divisor;
        /** Line control register */
        uint8_t lcr;
};

/** Symbolic names for port indexes */
enum uart_port {
        COM1 = 1,
        COM2 = 2,
        COM3 = 3,
        COM4 = 4,
};

#include <bits/uart.h>

void uart_write ( struct uart *uart, unsigned int addr, uint8_t data );
uint8_t uart_read ( struct uart *uart, unsigned int addr );
int uart_select ( struct uart *uart, unsigned int port );

/**
 * Check if received data is ready
 *
 * @v uart              UART
 * @ret ready           Data is ready
 */
static inline int uart_data_ready ( struct uart *uart ) {
        uint8_t lsr;

        lsr = uart_read ( uart, UART_LSR );
        return ( lsr & UART_LSR_DR );
}

/**
 * Receive data
 *
 * @v uart              UART
 * @ret data            Data
 */
static inline uint8_t uart_receive ( struct uart *uart ) {

        return uart_read ( uart, UART_RBR );
}

extern void uart_transmit ( struct uart *uart, uint8_t data );
extern void uart_flush ( struct uart *uart );
extern int uart_exists ( struct uart *uart );
extern int uart_init ( struct uart *uart, unsigned int baud, uint8_t lcr );

#endif /* _IPXE_UART_H */