File content as of revision 181:57724642e740:

/* mbed Microcontroller Library
 * Copyright (c) 2006-2013 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
// math.h required for floating point operations for baud rate calculation
#include "mbed_assert.h"
#include <math.h>
#include <string.h>
#include <stdlib.h>

#include "serial_api.h"
#include "cmsis.h"
#include "pinmap.h"

/******************************************************************************
 * INITIALIZATION
 ******************************************************************************/
#define UART_NUM    1

static const PinMap PinMap_UART_TX[] = {
    {P0_19, UART_0, 1},
    {P1_13, UART_0, 3},
    {P1_27, UART_0, 2},
    { NC  , NC    , 0}
};

static const PinMap PinMap_UART_RX[] = {
    {P0_18, UART_0, 1},
    {P1_14, UART_0, 3},
    {P1_26, UART_0, 2},
    {NC   , NC    , 0}
};

static uint32_t serial_irq_ids[UART_NUM] = {0};
static uart_irq_handler irq_handler;

int stdio_uart_inited = 0;
serial_t stdio_uart;

void serial_init(serial_t *obj, PinName tx, PinName rx) {
    int is_stdio_uart = 0;
    
    // determine the UART to use
    UARTName uart_tx = (UARTName)pinmap_peripheral(tx, PinMap_UART_TX);
    UARTName uart_rx = (UARTName)pinmap_peripheral(rx, PinMap_UART_RX);
    UARTName uart = (UARTName)pinmap_merge(uart_tx, uart_rx);
    MBED_ASSERT((int)uart != NC);
    
    obj->uart = (LPC_USART_Type *)uart;
    LPC_SYSCON->SYSAHBCLKCTRL |= (1<<12);
    
    // [TODO] Consider more elegant approach
    // disconnect USBTX/RX mapping mux, for case when switching ports
    //pin_function(USBTX, 0);
    //pin_function(USBRX, 0);
    
    // enable fifos and default rx trigger level
    obj->uart->FCR = 1 << 0  // FIFO Enable - 0 = Disables, 1 = Enabled
                   | 0 << 1  // Rx Fifo Reset
                   | 0 << 2  // Tx Fifo Reset
                   | 0 << 6; // Rx irq trigger level - 0 = 1 char, 1 = 4 chars, 2 = 8 chars, 3 = 14 chars
    
    // disable irqs
    obj->uart->IER = 0 << 0  // Rx Data available irq enable
                   | 0 << 1  // Tx Fifo empty irq enable
                   | 0 << 2; // Rx Line Status irq enable
    
    // set default baud rate and format
    serial_baud  (obj, 9600);
    serial_format(obj, 8, ParityNone, 1);
    
    // pinout the chosen uart
    pinmap_pinout(tx, PinMap_UART_TX);
    pinmap_pinout(rx, PinMap_UART_RX);
    
    // set rx/tx pins in PullUp mode
    if (tx != NC) {
        pin_mode(tx, PullUp);
    }
    if (rx != NC) {
        pin_mode(rx, PullUp);
    }
    
    switch (uart) {
        case UART_0: obj->index = 0; break;
    }
    
    is_stdio_uart = (uart == STDIO_UART) ? (1) : (0);
    
    if (is_stdio_uart) {
        stdio_uart_inited = 1;
        memcpy(&stdio_uart, obj, sizeof(serial_t));
    }
}

void serial_free(serial_t *obj) {
    serial_irq_ids[obj->index] = 0;
}

// serial_baud
// set the baud rate, taking in to account the current SystemFrequency
void serial_baud(serial_t *obj, int baudrate) {
    LPC_SYSCON->UARTCLKDIV = 0x1;
    uint32_t PCLK = SystemCoreClock;
    // First we check to see if the basic divide with no DivAddVal/MulVal
    // ratio gives us an integer result. If it does, we set DivAddVal = 0,
    // MulVal = 1. Otherwise, we search the valid ratio value range to find
    // the closest match. This could be more elegant, using search methods
    // and/or lookup tables, but the brute force method is not that much
    // slower, and is more maintainable.
    uint16_t DL = PCLK / (16 * baudrate);
    
    uint8_t DivAddVal = 0;
    uint8_t MulVal = 1;
    int hit = 0;
    uint16_t dlv;
    uint8_t mv, dav;
    if ((PCLK % (16 * baudrate)) != 0) {     // Checking for zero remainder
        int err_best = baudrate, b;
        for (mv = 1; mv < 16 && !hit; mv++)
        {
            for (dav = 0; dav < mv; dav++)
            {
                // baudrate = PCLK / (16 * dlv * (1 + (DivAdd / Mul))
                // solving for dlv, we get dlv = mul * PCLK / (16 * baudrate * (divadd + mul))
                // mul has 4 bits, PCLK has 27 so we have 1 bit headroom which can be used for rounding
                // for many values of mul and PCLK we have 2 or more bits of headroom which can be used to improve precision
                // note: X / 32 doesn't round correctly. Instead, we use ((X / 16) + 1) / 2 for correct rounding

                if ((mv * PCLK * 2) & 0x80000000) // 1 bit headroom
                    dlv = ((((2 * mv * PCLK) / (baudrate * (dav + mv))) / 16) + 1) / 2;
                else // 2 bits headroom, use more precision
                    dlv = ((((4 * mv * PCLK) / (baudrate * (dav + mv))) / 32) + 1) / 2;

                // datasheet says if DLL==DLM==0, then 1 is used instead since divide by zero is ungood
                if (dlv == 0)
                    dlv = 1;

                // datasheet says if dav > 0 then DL must be >= 2
                if ((dav > 0) && (dlv < 2))
                    dlv = 2;

                // integer rearrangement of the baudrate equation (with rounding)
                b = ((PCLK * mv / (dlv * (dav + mv) * 8)) + 1) / 2;

                // check to see how we went
                b = abs(b - baudrate);
                if (b < err_best)
                {
                    err_best  = b;

                    DL        = dlv;
                    MulVal    = mv;
                    DivAddVal = dav;

                    if (b == baudrate)
                    {
                        hit = 1;
                        break;
                    }
                }
            }
        }
    }
    
    // set LCR[DLAB] to enable writing to divider registers
    obj->uart->LCR |= (1 << 7);
    
    // set divider values
    obj->uart->DLM = (DL >> 8) & 0xFF;
    obj->uart->DLL = (DL >> 0) & 0xFF;
    obj->uart->FDR = (uint32_t) DivAddVal << 0
                   | (uint32_t) MulVal    << 4;
    
    // clear LCR[DLAB]
    obj->uart->LCR &= ~(1 << 7);
}

void serial_format(serial_t *obj, int data_bits, SerialParity parity, int stop_bits) {
    MBED_ASSERT((stop_bits == 1) || (stop_bits == 2)); // 0: 1 stop bits, 1: 2 stop bits
    MBED_ASSERT((data_bits > 4) && (data_bits < 9)); // 0: 5 data bits ... 3: 8 data bits
    MBED_ASSERT((parity == ParityNone) || (parity == ParityOdd) || (parity == ParityEven) ||
           (parity == ParityForced1) || (parity == ParityForced0));

    stop_bits -= 1;
    data_bits -= 5;

    int parity_enable, parity_select;
    switch (parity) {
        case ParityNone: parity_enable = 0; parity_select = 0; break;
        case ParityOdd : parity_enable = 1; parity_select = 0; break;
        case ParityEven: parity_enable = 1; parity_select = 1; break;
        case ParityForced1: parity_enable = 1; parity_select = 2; break;
        case ParityForced0: parity_enable = 1; parity_select = 3; break;
        default:
            break;
    }
    
    obj->uart->LCR = data_bits            << 0
                   | stop_bits            << 2
                   | parity_enable        << 3
                   | parity_select        << 4;
}

/******************************************************************************
 * INTERRUPTS HANDLING
 ******************************************************************************/
static inline void uart_irq(uint32_t iir, uint32_t index) {
    // [Chapter 14] LPC17xx UART0/2/3: UARTn Interrupt Handling
    SerialIrq irq_type;
    switch (iir) {
        case 1: irq_type = TxIrq; break;
        case 2: irq_type = RxIrq; break;
        default: return;
    }
    
    if (serial_irq_ids[index] != 0)
        irq_handler(serial_irq_ids[index], irq_type);
}

void uart0_irq() {uart_irq((LPC_USART->IIR >> 1) & 0x7, 0);}

void serial_irq_handler(serial_t *obj, uart_irq_handler handler, uint32_t id) {
    irq_handler = handler;
    serial_irq_ids[obj->index] = id;
}

void serial_irq_set(serial_t *obj, SerialIrq irq, uint32_t enable) {
    IRQn_Type irq_n = (IRQn_Type)0;
    uint32_t vector = 0;
    switch ((int)obj->uart) {
        case UART_0: irq_n=USART_IRQn ; vector = (uint32_t)&uart0_irq; break;
    }
    
    if (enable) {
        obj->uart->IER |= 1 << irq;
        NVIC_SetVector(irq_n, vector);
        NVIC_EnableIRQ(irq_n);
    } else { // disable
        int all_disabled = 0;
        SerialIrq other_irq = (irq == RxIrq) ? (TxIrq) : (RxIrq);

        obj->uart->IER &= ~(1 << irq);
        all_disabled = (obj->uart->IER & (1 << other_irq)) == 0;
        
        if (all_disabled)
            NVIC_DisableIRQ(irq_n);
    }
}

/******************************************************************************
 * READ/WRITE
 ******************************************************************************/
int serial_getc(serial_t *obj) {
    while (!serial_readable(obj));
    return obj->uart->RBR;
}

void serial_putc(serial_t *obj, int c) {
    while (!serial_writable(obj));
    obj->uart->THR = c;
}

int serial_readable(serial_t *obj) {
    return obj->uart->LSR & 0x01;
}

int serial_writable(serial_t *obj) {
    return obj->uart->LSR & 0x20;
}

void serial_clear(serial_t *obj) {
    obj->uart->FCR = 1 << 1  // rx FIFO reset
                   | 1 << 2  // tx FIFO reset
                   | 0 << 6; // interrupt depth
}

void serial_pinout_tx(PinName tx) {
    pinmap_pinout(tx, PinMap_UART_TX);
}

void serial_break_set(serial_t *obj) {
    obj->uart->LCR |= (1 << 6);
}

void serial_break_clear(serial_t *obj) {
    obj->uart->LCR &= ~(1 << 6);
}