/***************************************************************************
 *   Copyright (C) 04/2013 by Olaf Rempel                                  *
 *   razzor@kopf-tisch.de                                                  *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; version 2 of the License,               *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/
#include <avr/io.h>
#include <avr/interrupt.h>

#define F_CPU 11059200
#include <util/delay.h>

/*
 * attiny2313
 * lfuse: 0xff (ext. crystal, slow rising power, max startup time)
 * hfuse: 0xdb (2.7V BOD)
 * efuse: 0xff (self Prog enabled)
 *
 * PB0 -> NC
 * PB1 -> reset-out
 * PB2 -> /WR SRAM
 * PB3 -> SRCK (shift register clock)
 * PB4 -> SER (shift register input)
 * PB5 -> CCK (counter clock)
 * PB6 -> RCK (counter and shift register store clock)
 * PB7 -> /OE (output enable counter, shift register, reset-out, A16)
 * PD0 <- RXD
 * PD1 -> TXD
 * PD2 <- /PowerFail
 * PD3 -> A16
 * PD4 -> /LED_GN
 * PD5 -> /LED_RT
 * PD6 -> /OE (output enable RAM and address buffer, counter clear)
 */

#define RESET_OUT       PORTB1
#define nRAM_WR         PORTB2
#define SREG_CLK        PORTB3
#define SREG_DAT        PORTB4
#define CNT_CLK         PORTB5
#define REG_STORE       PORTB6
#define nEMU_EN         PORTB7

#define RXD             PORTD0
#define TXD             PORTD1
#define nPOWERFAIL      PORTD2
#define EMU_A16         PORTD3
#define nLED_GN         PORTD4
#define nLED_RT         PORTD5
#define nTARGET_EN      PORTD6

#define BAUDRATE        115200

#define UART_CALC_BAUDRATE(baudRate) (((uint32_t)F_CPU) / (((uint32_t)baudRate)*16) -1)

/* ************************************************************************* */

#define MSGTYPE_VERSION_REQ     0x01    /* no payload */
#define MSGTYPE_PAGESIZE_REQ    0x02    /* no payload */
#define MSGTYPE_CONFIG_REQ      0x03    /* eprom_type(1), pagesize(1), reset_polarity(1) */
#define MSGTYPE_PROGMODE_REQ    0x04    /* progmode(1) */
#define MSGTYPE_SETADDRESS_REQ  0x05    /* address(3) msb first */
#define MSGTYPE_WRITE_REQ       0x06    /* data(0-pagesize) */
#define MSGTYPE_READ_REQ        0x07    /* length(1) */

#define MSGTYPE_ERROR_RSP       0x80    /* error_code(1) */
#define MSGTYPE_VERSION_RSP     0x81    /* version(?) */
#define MSGTYPE_PAGESIZE_RSP    0x82    /* pagesize(1) */
#define MSGTYPE_CONFIG_RSP      0x83    /* no payload */
#define MSGTYPE_PROGMODE_RSP    0x84    /* no payload */
#define MSGTYPE_SETADDRESS_RSP  0x85    /* no payload */
#define MSGTYPE_WRITE_RSP       0x86    /* no payload */
#define MSGTYPE_READ_RSP        0x87    /* data(0-pagesize) */

#define SUCCESS                 0x00
#define ERROR_UNKNOWN_COMMAND   0x01    /* unknown message type */
#define ERROR_NOT_SUPPORTED     0x02    /* command not supported */
#define ERROR_INVALID_MODE      0x03    /* invalid progmode */
#define ERROR_INVALID_PARAMETER 0x04    /* invalid parameter in request */
#define ERROR_INVALID_ADDRESS   0x05    /* write outside of configured region */

#define RESET_POLARITY_LOW      0x00    /* low active reset */
#define RESET_POLARITY_HIGH     0x01    /* high active reset */

#define EPROM_TYPE_2K           0x02    /* 2716 */
#define EPROM_TYPE_4K           0x04    /* 2732 */
#define EPROM_TYPE_8K           0x08    /* 2764 */
#define EPROM_TYPE_16K          0x10    /* 27128 */
#define EPROM_TYPE_32K          0x20    /* 27256 */
#define EPROM_TYPE_64K          0x40    /* 27512 */
#define EPROM_TYPE_128K         0x80    /* 27010 */

#define PROGMODE_DISABLED       0x00    /* target running, no write access to RAM */
#define PROGMODE_ENABLED        0x01    /* target reset, write access to RAM */

#define PAGESIZE_MAX            128

/* ************************************************************************* */

struct _globdata {
    uint32_t    address_max;
    uint32_t    address;

    uint8_t     progmode;
    uint8_t     reset_polarity;
    uint8_t     pagesize;

    uint8_t     address_mask;
};

static const uint8_t version_str[] = "epromsim v1.00";
static struct _globdata gdata = { 0 };


/* *************************************************************************
 * send one byte to UART
 * ************************************************************************* */
static void ser_send(uint8_t data)
{
    loop_until_bit_is_set(UCSRA, UDRIE);
    UDR = data;
} /* ser_send */


/* *************************************************************************
 * receive one byte from UART
 * ************************************************************************* */
static uint8_t ser_recv(void)
{
    loop_until_bit_is_set(UCSRA, RXC);
    return UDR;
} /* ser_recv */


/* *************************************************************************
 * shift one byte out to register (LSB first)
 * ************************************************************************* */
static void shift_data(uint8_t data)
{
    uint8_t mask;

    for (mask = 0x01; mask != 0; mask <<= 1)
    {
        if (data & mask)
        {
            PORTB |= (1<<SREG_DAT);
        }
        else
        {
            PORTB &= ~(1<<SREG_DAT);
        }

        /* positive edge clocks in data */
        PORTB |= (1<<SREG_CLK);
        PORTB &= ~(1<<SREG_CLK);
    }
} /* shift_data */


/* *************************************************************************
 * store pulse for register and counter
 * ************************************************************************* */
static void store_pulse(void)
{
    /* positive edge transfers data to output buffer */
    PORTB |= (1<<REG_STORE);
    PORTB &= ~(1<<REG_STORE);
} /* store_pulse */


/* *************************************************************************
 * write pulse for SRAM
 * ************************************************************************* */
static void write_pulse(void)
{
    /* positive edge clocks in data */
    PORTB &= ~(1<<nRAM_WR);
    PORTB |= (1<<nRAM_WR);
} /* write_pulse */


/* *************************************************************************
 * reset address counter
 * ************************************************************************* */
static void address_reset(void)
{
    PORTD &= ~(1<<nTARGET_EN);
    PORTD |= (1<<nTARGET_EN);
} /* address_reset */


/* *************************************************************************
 * increment address counter
 * ************************************************************************* */
static void address_inc_pulse(void)
{
    /* positive edge increments counter */
    PORTB |= (1<<CNT_CLK);
    PORTB &= ~(1<<CNT_CLK);
} /* address_inc_pulse */


/* *************************************************************************
 * controls A16 line
 * ************************************************************************* */
static void address_set_a16(uint8_t enable)
{
    if (enable)
    {
        PORTD |= (1<<EMU_A16);
    }
    else
    {
        PORTD &= ~(1<<EMU_A16);
    }
} /* address_set_a16 */


/* *************************************************************************
 * switch access to RAM between emulator and target
 * ************************************************************************* */
static void set_progmode(uint8_t progmode)
{
    gdata.progmode = progmode;

    if (progmode)
    {
        /* switch RAM access to EMU */
        PORTD |= (1<<nTARGET_EN);
        PORTD &= ~(1<<nLED_RT);
        PORTB &= ~(1<<nEMU_EN);
    }
    else
    {
        /* set eprom address line mask */
        shift_data(gdata.address_mask);
        shift_data(0x00);
        store_pulse();

        /* switch RAM access to TARGET */
        PORTB |= (1<<nEMU_EN);
        PORTD &= ~(1<<nTARGET_EN);
        PORTD |= (1<<nLED_RT);

        /* address counter is reset */
        gdata.address = 0x00;
    }

    /* set RESET_OUT */
    if (progmode ^ gdata.reset_polarity)
    {
        PORTB &= ~(1<<RESET_OUT);
    }
    else
    {
        PORTB |= (1<<RESET_OUT);
    }
} /* set_progmode */


/* *************************************************************************
 * set_address
 * ************************************************************************* */
static void set_address(uint32_t address)
{
    /* reset address counter */
    if (address < gdata.address)
    {
        address_reset();
        gdata.address = 0;
    }

    // TODO: A16 is not controlled by counter

    while (gdata.address++ < address)
    {
        address_inc_pulse();
    }
} /* set_address */


/* *************************************************************************
 * write_data
 * ************************************************************************* */
static void write_data(uint8_t length)
{
    while (length--)
    {
        address_set_a16(gdata.address++ > 0xFFFF);

        shift_data(ser_recv());
        store_pulse();
        write_pulse();
        address_inc_pulse();
    }
} /* write_data */


/* *************************************************************************
 * fill RAM with 0xFF
 * ************************************************************************* */
static void do_clear(void)
{
    uint16_t i = 0xFFFF;

    shift_data(0xFF);

    PORTD &= ~(1<<EMU_A16);
    do {
        store_pulse();
        write_pulse();
        address_inc_pulse();
    } while (i--);

    PORTD |= (1<<EMU_A16);
    do {
        store_pulse();
        write_pulse();
        address_inc_pulse();
    } while (i--);
} /* do_clear */


/* *************************************************************************
 * configures number of addresslines
 * ************************************************************************* */
static uint8_t set_eprom_type(uint8_t type)
{
    switch (type)
    {
        case EPROM_TYPE_2K:
            gdata.address_max   = 0x0800;
            gdata.address_mask  = 0x00;
            break;

        case EPROM_TYPE_4K:
            gdata.address_max   = 0x1000;
            gdata.address_mask  = 0x80;
            break;

        case EPROM_TYPE_8K:
            gdata.address_max   = 0x2000;
            gdata.address_mask  = 0xC0;
            break;

        case EPROM_TYPE_16K:
            gdata.address_max   = 0x4000;
            gdata.address_mask  = 0xE0;
            break;

        case EPROM_TYPE_32K:
            gdata.address_max   = 0x8000;
            gdata.address_mask  = 0xF0;
            break;

        case EPROM_TYPE_64K:
            gdata.address_max   = 0x10000;
            gdata.address_mask  = 0xF8;
            break;

        case EPROM_TYPE_128K:
            gdata.address_max   = 0x20000;
            gdata.address_mask  = 0xFC;
            break;

        default:
            return ERROR_INVALID_PARAMETER;
    }

    return SUCCESS;
} /* set_eprom_type */


#if 0
/* Powerfail / Wakeup */
ISR(INT0_vect)
{
    if (1) {
        /*
         * Power Fail:
         * - enable RESET_OUT
         * - disable nTARGET_EN
         * - enable rising edge INT0 (nPOWERFAIL)
         * - disable pullups
         * - put MCU in standby
         */
        do_reset(1);

        /* disable green LED */
        PORTD |= (1<<nLED_GN);
    } else {
        /*
         * Power Restore:
         * - enable pullups
         * - enable falling edge INT0 (nPOWERFAIL)
         * - enable nTARGET_EN again
         * - disable RESET_OUT
         */

        /* enable green LED */
        PORTD &= ~(1<<nLED_GN);

        do_reset(0);
    }
}
#endif


int main(void) __attribute__ ((noreturn));
int main(void)
{
    DDRB = 0xFF;
    PORTB = (1<<nRAM_WR) | (1<<nEMU_EN);

    DDRD = ~((1<<RXD) | (1<<nPOWERFAIL));
    PORTD = (1<<RXD) | (1<<nPOWERFAIL) | (1<<nLED_GN) | (1<<nLED_RT) | (1<<nTARGET_EN);

    /* enable UART 115200,8n1 */
    UBRRH = (UART_CALC_BAUDRATE(BAUDRATE)>>8) & 0xFF;
    UBRRL = (UART_CALC_BAUDRATE(BAUDRATE) & 0xFF);
    UCSRC = (1<<UCSZ1) | (1<<UCSZ0);
    UCSRB = (1<<RXEN) | (1<<TXEN);

#if 0
    /* powerfail: detect falling edge on INT0 */
    MCUCR = (1<<ISC01);
    GIMSK = (1<<INT0);
    sei();
#endif

    /* enable LED and reset Counter */
    PORTD &= ~((1<<nLED_GN) | (1<<nTARGET_EN));

    /* init RAM */
    set_eprom_type(EPROM_TYPE_128K);
    set_progmode(PROGMODE_ENABLED);
    do_clear();
    set_progmode(PROGMODE_DISABLED);

    while (1)
    {
        uint8_t msgtype = ser_recv();
        uint8_t length = ser_recv();
        uint8_t error_code = ERROR_INVALID_PARAMETER;

        switch (msgtype)
        {
            case MSGTYPE_VERSION_REQ:
                if (length == 0x00)
                {
                    ser_send(MSGTYPE_VERSION_RSP);
                    ser_send(sizeof(version_str) -1);

                    const uint8_t * p_data = version_str;
                    while (*p_data)
                    {
                        ser_send(*p_data++);
                    }

                    error_code = SUCCESS;
                }
                break;

            case MSGTYPE_PAGESIZE_REQ:
                if (length == 0x00)
                {
                    ser_send(MSGTYPE_PAGESIZE_RSP);
                    ser_send(0x01);
                    ser_send(PAGESIZE_MAX);

                    error_code = SUCCESS;
                }
                break;

            case MSGTYPE_CONFIG_REQ:
                if (length == 0x03)
                {
                    uint8_t eprom_type = ser_recv();
                    uint8_t pagesize = ser_recv();
                    uint8_t reset_polarity = ser_recv();

                    if (gdata.progmode == PROGMODE_ENABLED)
                    {
                        error_code = ERROR_INVALID_MODE;
                    }
                    else
                    {
                        if ((reset_polarity <= RESET_POLARITY_HIGH) &&
                            (pagesize <= PAGESIZE_MAX) &&
                            (set_eprom_type(eprom_type) == SUCCESS)
                           )
                        {
                            gdata.pagesize = pagesize;
                            gdata.reset_polarity = reset_polarity;

                            ser_send(MSGTYPE_CONFIG_RSP);
                            ser_send(0x00);
                            error_code = SUCCESS;
                        }
                    }
                }
                break;

            case MSGTYPE_PROGMODE_REQ:
                if (length == 0x01)
                {
                    uint8_t progmode = ser_recv();

                    if (progmode <= PROGMODE_ENABLED)
                    {
                        set_progmode(progmode);

                        ser_send(MSGTYPE_PROGMODE_RSP);
                        ser_send(0x00);
                        error_code = SUCCESS;
                    }
                }
                break;

            case MSGTYPE_SETADDRESS_REQ:
                if (length == 0x03)
                {
                    uint32_t address;

                    address = ser_recv();
                    address = (address << 8) | ser_recv();
                    address = (address << 8) | ser_recv();

                    if (address < gdata.address_max)
                    {
                        if (gdata.progmode == PROGMODE_DISABLED)
                        {
                            error_code = ERROR_INVALID_MODE;
                        }
                        else
                        {
                            set_address(address);

                            ser_send(MSGTYPE_SETADDRESS_RSP);
                            ser_send(0x00);
                            error_code = SUCCESS;
                        }
                    }
                }
                break;

            case MSGTYPE_WRITE_REQ:
                if ((length > 0) &&
                    (length <= gdata.pagesize)
                   )
                {
                    if ((gdata.address >= gdata.address_max) ||
                        ((gdata.address + length) > gdata.address_max)
                       )
                    {
                        error_code = ERROR_INVALID_ADDRESS;
                    }
                    else if (gdata.progmode == PROGMODE_DISABLED)
                    {
                        error_code = ERROR_INVALID_MODE;
                    }
                    else
                    {
                        write_data(length);

                        ser_send(MSGTYPE_WRITE_RSP);
                        ser_send(0x00);
                        error_code = SUCCESS;
                    }
                }
                break;

            case MSGTYPE_READ_REQ:
                error_code = ERROR_NOT_SUPPORTED;
                break;

            default:
                error_code = ERROR_UNKNOWN_COMMAND;
                break;
        }

        if (error_code != SUCCESS)
        {
            /* read remaining request */
            while (length--)
            {
                (void)ser_recv();
            }

            ser_send(MSGTYPE_ERROR_RSP);
            ser_send(0x01);
            ser_send(error_code);
        }
    }
} /* main */