rockbox/apps/plugins/alpine_cdc.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 *
 * Copyright (C) 2003-2005 Jörg Hohensohn
 *
 * Alpine CD changer Project
 * This is a feasibility study for Archos emulating an Alpine M-Bus CD changer.
 * 
 * Currently it will do seeks and change tracks, but nothing like disks.
 * The debug version shows a dump of the M-Bus communication on screen.
 *
 * Usage: Start plugin, it will stay in the background and do the emulation.
 * You need to make an adapter with an 8-pin DIN plug for the radio at one end
 * and a 4-ring 3.5 mm plug for the Archos headphone jack at the other.
 * The Archos remote pin connects to the M-Bus, audio as usual.
 *
 * 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; either version 2
 * of the License, or (at your option) any later version.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/

#include "plugin.h"

#ifdef HAVE_LCD_CHARCELLS /* player model */
#define LINES    2
#define COLUMNS 11
#else /* recorder models */
#define LINES    8
#define COLUMNS 32 /* can't really tell for proportional font */
#endif

/****************** imports ******************/

#include "sh7034.h"
#include "system.h"

/****************** constants ******************/

/* measured bit time on the M-Bus is 3.075 ms = 325.2 Hz */
#define MBUS_BAUDRATE 3252 /* make it 10 * bittime */
#define MBUS_STEP_FREQ (MBUS_BAUDRATE/2) /* 5 steps per bit */
#define MBUS_BIT_FREQ (MBUS_BAUDRATE/10) /* the true bit frequency again */

#define MBUS_MAX_SIZE      16 /* maximum length of an M-Bus packet, incl. checksum */
#define MBUS_RCV_QUEUESIZE  4 /* how many packets can be queued by receiver */

#define ERI1  (*((volatile unsigned long*)0x090001A0)) /* RX error */
#define RXI1  (*((volatile unsigned long*)0x090001A4)) /* RX */

#define PB10 0x0400

/* receive status */
#define RX_BUSY      0 /* reception in progress */
#define RX_RECEIVED  1 /* valid data available */
#define RX_FRAMING   2 /* frame error */
#define RX_OVERRUN   3 /* receiver overrun */
#define RX_PARITY    4 /* parity error */
#define RX_SYMBOL    5 /* invalid bit timing */
#define RX_OVERFLOW  6 /* buffer full */
#define RX_OVERLAP   7 /* receive interrupt while transmitting */

/* timer operation mode */
#define TM_OFF        0 /* not in use */
#define TM_TRANSMIT   1 /* periodic timer to transmit */
#define TM_RX_TIMEOUT 2 /* single shot for receive timeout */

/* emulation play state */
#define EMU_IDLE      0
#define EMU_PREPARING 1
#define EMU_STOPPED   2
#define EMU_PAUSED    3
#define EMU_PLAYING   4
#define EMU_SPINUP    5
#define EMU_FF        6
#define EMU_FR        7


/****************** prototypes ******************/

void timer_init(unsigned hz, unsigned to); /* setup static timer registers and values */
void timer_set_mode(int mode); /* define for what the timer should be used right now */
void timer4_isr(void); /* IMIA4 ISR */

void transmit_isr(void); /* 2nd level ISR for M-Bus transmission */

void uart_init(unsigned baudrate); /* UART setup */
void uart_rx_isr(void) __attribute__((interrupt_handler)); /* RXI1 ISR */
void uart_err_isr(void) __attribute__((interrupt_handler)); /* ERI1 ISR */
void receive_timeout_isr(void); /* 2nd level ISR for receiver timeout */

void mbus_init(void); /* prepare the M-Bus layer */
int mbus_send(unsigned char* p_msg, int digits); /* packet send */
int mbus_receive(unsigned char* p_msg, unsigned bufsize, int timeout); /* packet receive */

unsigned char calc_checksum(unsigned char* p_msg, int digits); /* make M-Bus checksum */
bool bit_test(unsigned char* buf, unsigned bit); /* test one bit of M-Bus packet */
void bit_set(unsigned char* buf, unsigned bit, bool val); /* set/clear one bit of M-Bus packet */

void print_scroll(char* string); /* implements a scrolling screen */
void dump_packet(char* dest, int dst_size, char* src, int n); /* convert packet to ASCII */

void emu_init(void); /* init changer emulation */
void emu_process_packet(unsigned char* mbus_msg, int msg_size); /* feed a received radio packet */
void emu_tick(void); /* for regular actions of the emulator */

int get_playtime(void); /* return the current track time in seconds */
int get_tracklength(void); /* return the total length of the current track */
void set_track(int selected);
int get_track(void); /* return the track number */
void set_play(void); /* start or resume playback */
void set_pause(void); /* pause playback */
void set_stop(void); /* stop playback */
void set_position(int seconds); /* seek */
void get_playmsg(void); /* update the play message with Rockbox info */
void get_diskmsg(void); /* update the disk status message with Rockbox info */

void sound_neutral(void); /* set to everything flat and 0 dB volume */
void sound_normal(void); /* return to user settings */

void thread(void); /* the thread running it all */
int main(const void* parameter); /* main loop */
enum plugin_status plugin_start(const void* parameter); /* entry */


/****************** data types ******************/

/* one entry in the receive queue */
typedef struct
{
    unsigned char buf[MBUS_MAX_SIZE]; /* message buffer */
    unsigned size; /* length of data in the buffer */
    unsigned error; /* error code from reception */
} t_rcv_queue_entry;


/****************** globals ******************/


/* information owned by the timer transmit ISR */
struct 
{
    unsigned char send_buf[MBUS_MAX_SIZE]; /* M-Bus message */
    unsigned send_size; /* current length of data in the buffer */
    unsigned index; /* index for which byte to send */
    unsigned byte; /* which byte to send */
    unsigned bitmask; /* which bit to send */
    unsigned step; /* where in the pulse are we */
    bool bit; /* currently sent bit */
    bool collision; /* set if a collision happened */
    bool busy; /* flag if in transmission */
} gSendIRQ;


/* information owned by the UART receive ISR */
struct 
{
    t_rcv_queue_entry queue[MBUS_RCV_QUEUESIZE]; /* M-Bus message queue */
    unsigned buf_read; /* readout maintained by the user application */
    unsigned buf_write; /* writing maintained by ISR */
    bool overflow; /* indicate queue overflow */
    unsigned byte; /* currently assembled byte */
    unsigned bit; /* which bit to receive */
} gRcvIRQ;


/* information owned by the timer */
struct
{
    unsigned mode; /* off, transmit, receive timout */
    unsigned transmit; /* value for transmit */
    unsigned timeout; /* value for receive timeout */
} gTimer;


/* information owned by the changer emulation */
struct
{
    unsigned char playmsg[15]; /* current play state msg */
    unsigned char changemsg[11]; /* changing message */
    unsigned char diskmsg[12]; /* disk status message */
    long poll_interval; /* call the emu each n ticks */
    int time; /* seconds within the song */
    int set_state; /* the desired state to change into */
} gEmu;


/* communication to the worker thread */
struct 
{
    bool foreground; /* set as long as we're owning the UI */
    bool exiting; /* signal to the thread that we want to exit */
    unsigned int thread; /* worker thread id */
} gTread;


/****************** implementation ******************/


/* setup static timer registers and values */
void timer_init(unsigned hz, unsigned to)
{
    rb->memset(&gTimer, 0, sizeof(gTimer));
    
    gTimer.transmit = TIMER_FREQ / hz; /* time for bit transitions */
    gTimer.timeout = TIMER_FREQ / to; /* time for receive timeout */
}


/* define for what the timer should be used right now */
void timer_set_mode(int mode)
{
    TCNT4 = 0; /* start counting at 0 */
    gTimer.mode = mode; /* store the mode */

    if (mode == TM_RX_TIMEOUT)
    {
        rb->timer_register(1, NULL, gTimer.timeout, timer4_isr IF_COP(, CPU));
        IPRD = (IPRD & 0xFF0F) | 11 << 4;  /* interrupt priority */
    }
    else if (mode == TM_TRANSMIT)
    {
        rb->timer_register(1, NULL, gTimer.transmit, timer4_isr IF_COP(, CPU));
        IPRD = (IPRD & 0xFF0F) | 14 << 4;  /* interrupt priority */
    }
    else
    {
        rb->timer_unregister();
    }
}


void timer4_isr(void) /* IMIA4 */
{
    switch (gTimer.mode)
    {   /* distribute the interrupt */
    case TM_TRANSMIT:
        transmit_isr();
        break;
    case TM_RX_TIMEOUT:
        receive_timeout_isr();
        rb->timer_unregister(); /* single shot */
        break;
    default:
        timer_set_mode(TM_OFF); /* spurious interrupt */
    } /* switch */
}


/* About Alpine M-Bus
 * ------------------
 *
 * The protocol uses a single wire in half duplex mode.
 * A bit like I2C, this wire is either pulled low or left floating high.
 * Bit time is ~3 ms, a "zero" is coded as ~0.6 ms low, a "one" as ~1.8 ms low.
 * Nice to view in a 0.6 ms grid:
 *
 *    0   0.6  1.2  1.8  2.4  3.0
 *    |    |    |    |    |    |
 *  __      ___________________
 *    \____/                   \    "zero" bit
 *  __                _________
 *    \______________/         \    "one" bit
 *
 * So I send out the data in a timer interrupt spawned to 0.6 ms.
 * In phases where the line is floating high, I can check for collisions.
 * (happens if the other side driving it low, too.)
 *
 * Data is transmitted in multiples of 4 bit, to ease BCD representation.
 */


/* 2nd level ISR for M-Bus transmission */
void transmit_isr(void)
{
    bool exit = false;

    TSR4 &= ~0x01; /* clear the interrupt */

    switch(gSendIRQ.step++)
    {
    case 0:
        and_b(~0x04, &PBDRH); /* low (read-modify-write access may have changed it while it was input) */
        or_b(0x04, &PBIORH); /* drive low (output) */
        break;
    case 1: /* 0.6 ms */
        if (!gSendIRQ.bit) /* sending "zero"? */
            and_b(~0x04, &PBIORH); /* float (input) */
        break;
    case 2: /* 1.2 ms */
        if (!gSendIRQ.bit && ((PBDR & PB10) == 0))
            gSendIRQ.collision = true;
        break;
    case 3: /* 1.8 ms */
        if (gSendIRQ.bit) /* sending "one"? */
            and_b(~0x04, &PBIORH); /* float (input) */
        else if ((PBDR & PB10) == 0)
            gSendIRQ.collision = true;
        break;
    case 4: /* 2.4 ms */
        if ((PBDR & PB10) == 0)
            gSendIRQ.collision = true;
        
        /* prepare next round */
        gSendIRQ.step = 0;
        gSendIRQ.bitmask >>= 1;
        if (gSendIRQ.bitmask)
        {   /* new bit */
            gSendIRQ.bit = (gSendIRQ.byte & gSendIRQ.bitmask) != 0;
        }
        else
        {   /* new byte */
            if (++gSendIRQ.index < gSendIRQ.send_size)
            {
                gSendIRQ.bitmask = 0x08;
                gSendIRQ.byte = gSendIRQ.send_buf[gSendIRQ.index];
                gSendIRQ.bit = (gSendIRQ.byte & gSendIRQ.bitmask) != 0;
            }
            else
                exit = true; /* done */
        }
        break;
    }

    if (exit || gSendIRQ.collision)
    {   /* stop transmission */
        or_b(0x20, PBCR1_ADDR+1); /* RxD1 again for PB10 */
        timer_set_mode(TM_OFF); /* stop the timer */
        gSendIRQ.busy = false; /* do this last, to avoid race conditions */
    }
}


/* For receiving, I use the "normal" serial RX feature of the CPU,
 * so we can receive within an interrupt, no line polling necessary.
 * Luckily, the M-Bus bit always starts with a falling edge and ends with a high,
 * this matches with the start bit and the stop bit of a serial transmission.
 * The baudrate is set such that the M-Bus bit time (ca. 3ms) matches
 * the serial reception time of one byte, so we receive one byte per
 * M-Bus bit.
 * Start bit, 8 data bits and stop bit (total=10) nicely fall into the 5
 * phases like above:
 *
 *    0      0.6     1.2     1.8     2.4     3.0 ms
 *    |       |       |       |       |       |    time
 *  __         _______________________________
 *    \_______/                               \    "zero" bit
 *  __                         _______________
 *    \_______________________/               \    "one" bit
 *
 *    |   |   |   |   |   |   |   |   |   |   |    serial sampling interval
 *    Start 0   1   2   3   4   5   6   7  Stop    bit (LSB first!)
 *
 * By looking at the bit pattern in the serial byte we can distinguish 
 * the short low from the longer low, tell "zero" and "one" apart.
 * So we receive 0xFE for a "zero", 0xE0 for a "one".
 * It may be necessary to treat the bits next to transitions as don't care,
 * in case the timing is not so accurate.
 * Bits are always sent "back-to-back", so I detect the packet end by timeout.
 */


void uart_init(unsigned baudrate) 
{
    RXI1 = (unsigned long)uart_rx_isr; /* install ISR */
    ERI1 = (unsigned long)uart_err_isr; /* install ISR */

    SCR1 = 0x00; /* disable everything; select async mode with SCK pin as I/O */
    SMR1 = 0x00; /* async, 8N1, NoMultiProc, sysclock/1 */
    BRR1 = ((FREQ/(32*baudrate))-1);
                 
    IPRE = (IPRE & ~0xf000) | 0xc000; /* interrupt on level 12 */

    rb->sleep(1); /* hardware needs to settle for at least one bit interval */

    and_b(~(SCI_RDRF | SCI_ORER | SCI_FER | SCI_PER), &SSR1); /* clear any receiver flag */
    or_b(SCI_RE | SCI_RIE , &SCR1); /* enable the receiver with interrupt */
}


void uart_rx_isr(void) /* RXI1 */
{
    unsigned char data;
    t_rcv_queue_entry* p_entry = &gRcvIRQ.queue[gRcvIRQ.buf_write]; /* short cut */
    
    data = RDR1; /* get data */
    
    and_b(~SCI_RDRF, &SSR1); /* clear data received flag */

    if (gTimer.mode == TM_TRANSMIT)
        p_entry->error = RX_OVERLAP; /* oops, we're also transmitting, stop */
    else
        timer_set_mode(TM_RX_TIMEOUT); /* (re)spawn timeout */

    if (p_entry->error != RX_BUSY)
        return;

    if ((data & ~0x00) == 0xFE) /* 01111111 in line order (reverse) */
    {   /* "zero" received */
        gRcvIRQ.byte <<= 1;
    }
    else if ((data & ~0x00) == 0xE0) /* 00000111 in line order (reverse) */
    {   /* "one" received */
        gRcvIRQ.byte = gRcvIRQ.byte << 1 | 0x01;
    }
    else
    {   /* unrecognized pulse */
        p_entry->error = RX_SYMBOL;
    }

    if (p_entry->error == RX_BUSY)
    {
        if (++gRcvIRQ.bit >= 4)
        {   /* byte completed */
            if (p_entry->size >= sizeof(p_entry->buf))
            {
                p_entry->error = RX_OVERFLOW; /* buffer full */
            }
            else
            {
                p_entry->buf[p_entry->size] = gRcvIRQ.byte;
                gRcvIRQ.byte = 0;
                gRcvIRQ.bit = 0;
                p_entry->size++;
            }
        }
    }
}


void uart_err_isr(void) /* ERI1 */
{
    t_rcv_queue_entry* p_entry = &gRcvIRQ.queue[gRcvIRQ.buf_write]; /* short cut */

    if (p_entry->error == RX_BUSY)
    {   /* terminate reception in case of error */
        if (SSR1 & SCI_FER) 
            p_entry->error = RX_FRAMING;
        else if (SSR1 & SCI_ORER)
            p_entry->error = RX_OVERRUN;
        else if (SSR1 & SCI_PER)
            p_entry->error = RX_PARITY;
    }

    /* clear any receiver flag */
    and_b(~(SCI_RDRF | SCI_ORER | SCI_FER | SCI_PER), &SSR1);
}


/* 2nd level ISR for receiver timeout, this finalizes reception */
void receive_timeout_isr(void)
{
    t_rcv_queue_entry* p_entry = &gRcvIRQ.queue[gRcvIRQ.buf_write]; /* short cut */

    timer_set_mode(TM_OFF); /* single shot */

    if (p_entry->error == RX_BUSY) /* everthing OK so far? */
        p_entry->error = RX_RECEIVED; /* end with valid data */

    /* move to next queue entry */
    gRcvIRQ.buf_write++;
    if (gRcvIRQ.buf_write >= MBUS_RCV_QUEUESIZE)
        gRcvIRQ.buf_write = 0;
    p_entry = &gRcvIRQ.queue[gRcvIRQ.buf_write];

    if (gRcvIRQ.buf_write == gRcvIRQ.buf_read)
    {   /* queue overflow */
        gRcvIRQ.overflow = true;
        /* what can I do? Continueing overwrites the oldest. */
    }

    gRcvIRQ.byte = 0;
    gRcvIRQ.bit = 0;
    p_entry->size = 0;
    p_entry->error = RX_BUSY; /* enable receive on new entry */
}


/* generate the checksum */
unsigned char calc_checksum(unsigned char* p_msg, int digits)
{
    int chk = 0;
    int i;
    
    for (i=0; i<digits; i++)
    {
        chk ^= p_msg[i];
    }
    chk = (chk+1) % 16;
    
    return chk;
}


/****************** high-level M-Bus functions ******************/

void mbus_init(void)
{
    /* init the send object */
    rb->memset(&gSendIRQ, 0, sizeof(gSendIRQ));
    timer_init(MBUS_STEP_FREQ, (MBUS_BIT_FREQ*10)/15); /* setup frequency and timeout (1.5 bit) */

    /* init receiver */
    rb->memset(&gRcvIRQ, 0, sizeof(gRcvIRQ));
    uart_init(MBUS_BAUDRATE);
}


/* send out a number of BCD digits (one per byte) with M-Bus protocol */
int mbus_send(unsigned char* p_msg, int digits)
{
    /* wait for previous transmit/receive to end */
    while(gTimer.mode != TM_OFF) /* wait for "free line" */
        rb->sleep(1);
    
    /* fill in our part */
    rb->memcpy(gSendIRQ.send_buf, p_msg, digits);

    /* add checksum */
    gSendIRQ.send_buf[digits] = calc_checksum(p_msg, digits);
    digits++;

    /* debug dump, to be removed */
    if (gTread.foreground)
    {
        char buf[MBUS_MAX_SIZE+1];
        dump_packet(buf, sizeof(buf), gSendIRQ.send_buf, digits);
        /*print_scroll(buf); */
    }

    gSendIRQ.send_size = digits;

    /* prepare everything so the ISR can start right away */
    gSendIRQ.index = 0;
    gSendIRQ.byte = gSendIRQ.send_buf[0];
    gSendIRQ.bitmask = 0x08;
    gSendIRQ.step = 0;
    gSendIRQ.bit = (gSendIRQ.byte & gSendIRQ.bitmask) != 0;
    gSendIRQ.collision = false;
    gSendIRQ.busy = true;

    /* last chance to wait for a new detected receive to end */
    while(gTimer.mode != TM_OFF) /* wait for "free line" */
        rb->sleep(1);
    
    and_b(~0x30, PBCR1_ADDR+1); /* GPIO for PB10 */
    timer_set_mode(TM_TRANSMIT); /* run */

    /* make the call blocking until sent out */
    rb->sleep(digits*4*HZ/MBUS_BIT_FREQ); /* should take this long */

    while(gSendIRQ.busy) /* poll in case it lasts longer */
        rb->sleep(1); /* (should not happen) */

    /* debug output, to be removed */
    if (gTread.foreground)
    {
        if (gSendIRQ.collision)
            print_scroll("collision");
    }

    return gSendIRQ.collision;
}


/* returns the size of message copy, 0 if timed out, negative on error */
int mbus_receive(unsigned char* p_msg, unsigned bufsize, int timeout)
{
    int retval = 0;

    do
    {
        if (gRcvIRQ.buf_read != gRcvIRQ.buf_write)
        {   /* something in the queue */
            t_rcv_queue_entry* p_entry = &gRcvIRQ.queue[gRcvIRQ.buf_read]; /* short cut */

            if (p_entry->error == RX_RECEIVED)
            {   /* seems valid */
                rb->memcpy(p_msg, p_entry->buf, MIN(p_entry->size, bufsize));
                retval = p_entry->size; /* return message size */
            }
            else
            {   /* an error occured */
                retval = - p_entry->error; /* return negative number */
            }
            
            /* next queue readout position */
            gRcvIRQ.buf_read++;
            if (gRcvIRQ.buf_read >= MBUS_RCV_QUEUESIZE)
                gRcvIRQ.buf_read = 0;

            return retval; /* exit */
        }
        
        if (timeout != 0 || gTimer.mode != TM_OFF) /* also carry on if reception in progress */
        {
            if (timeout != -1 && timeout != 0) /* if not infinite or expired */
                timeout--;
    
            rb->sleep(1); /* wait a while */
        }

    } while (timeout != 0 || gTimer.mode != TM_OFF);

    return 0; /* timeout */
}


/****************** MMI helper fuctions ******************/


void print_scroll(char* string)
{
    static char screen[LINES][COLUMNS+1]; /* visible strings */
    static unsigned pos = 0; /* next print position */
    static unsigned screentop = 0; /* for scrolling */

    if (!gTread.foreground)
        return; /* just to protect careless callers */

    if (pos >= LINES)
    {   /* need to scroll first */
        int i;
        rb->lcd_clear_display();
        screentop++;
        for (i=0; i<LINES-1; i++)
            rb->lcd_puts(0, i, screen[(i+screentop) % LINES]);

        pos = LINES-1;
    }
    
    /* no strncpy avail. */
    rb->snprintf(screen[(pos+screentop) % LINES], sizeof(screen[0]), "%s", string);

    rb->lcd_puts(0, pos, screen[(pos+screentop) % LINES]);
    rb->lcd_update();
    pos++;
}


void dump_packet(char* dest, int dst_size, char* src, int n)
{
    int i;
    int len = MIN(dst_size-1, n);

    for (i=0; i<len; i++)
    {   /* convert to hex digits */
        dest[i] = src[i] < 10 ? '0' + src[i] : 'A' + src[i] - 10;
    }
    dest[i] = '\0'; /* zero terminate string */
}


/****************** CD changer emulation ******************/

bool bit_test(unsigned char* buf, unsigned bit)
{
    return (buf[bit>>2] & BIT_N(bit&3)) != 0;
}


void bit_set(unsigned char* buf, unsigned bit, bool val)
{
    if (val)
        buf[bit>>2] |= BIT_N(bit&3);
    else
        buf[bit>>2] &= ~BIT_N(bit&3);
}


void emu_init(void)
{
    rb->memset(&gEmu, 0, sizeof(gEmu));

    gEmu.poll_interval = HZ;

    /* init the play message to 990000000000000 */
    gEmu.playmsg[0] = gEmu.playmsg[1] = 0x9;

    /* init the changing message to 9B900000001 */
    gEmu.changemsg[0] = gEmu.changemsg[2] = 0x9;
    gEmu.changemsg[1] = 0xB;
    gEmu.changemsg[10] = 0x1;

    /* init the disk status message to 9C1019999990 */
    rb->memset(&gEmu.diskmsg, 0x9, sizeof(gEmu.diskmsg));
    gEmu.diskmsg[1] = 0xC;
    gEmu.diskmsg[2] = gEmu.diskmsg[4] = 0x1;
    gEmu.diskmsg[3] = gEmu.diskmsg[11] = 0x0;
}

/* feed a radio command into the emulator */
void emu_process_packet(unsigned char* mbus_msg, int msg_size)
{
    bool playmsg_dirty = false;
    bool diskmsg_dirty = false;

    if (msg_size == 2 && mbus_msg[0] == 1 && mbus_msg[1] == 8)
    {   /* 18: ping */
        mbus_send("\x09\x08", 2); /* 98: ping OK */
    }
    else if (msg_size == 5 && mbus_msg[0] == 1 && mbus_msg[1] == 1 && mbus_msg[2] == 1)
    {   /* set play state */
        if (bit_test(mbus_msg, 16))
        {
            if (gEmu.set_state == EMU_FF || gEmu.set_state == EMU_FR) /* was seeking? */
            {   /* seek to final position */
                set_position(gEmu.time);
            }
            else if (gEmu.set_state != EMU_PLAYING || gEmu.set_state != EMU_PAUSED)
            {   /* was not playing yet, better send disk message */
                diskmsg_dirty = true;
            }
            set_play();
            gEmu.set_state = EMU_PLAYING;
            playmsg_dirty = true;
        }
        
        if (bit_test(mbus_msg, 17))
        {
            gEmu.set_state = EMU_PAUSED;
            playmsg_dirty = true;
            set_pause();
        }
        
        if (bit_test(mbus_msg, 14))
        {
            gEmu.set_state = EMU_STOPPED;
            playmsg_dirty = true;
            set_stop();
        }

        if (bit_test(mbus_msg, 18))
        {
            gEmu.set_state = EMU_FF;
            playmsg_dirty = true;
            set_pause();
        }

        if (bit_test(mbus_msg, 19))
        {
            gEmu.set_state = EMU_FR;
            playmsg_dirty = true;
            set_pause();
        }

        if (bit_test(mbus_msg, 12)) /* scan stop */
        {
            bit_set(gEmu.playmsg, 51, false);
            playmsg_dirty = true;
        }

        if (gEmu.set_state == EMU_FF || gEmu.set_state == EMU_FR)
            gEmu.poll_interval = HZ/4; /* faster refresh */
        else
            gEmu.poll_interval = HZ;
    }
    else if (msg_size == 8 && mbus_msg[0] == 1 && mbus_msg[1] == 1 && mbus_msg[2] == 4)
    {   /* set program mode */
        gEmu.playmsg[11] = mbus_msg[3]; /* copy repeat, random, intro */
        gEmu.playmsg[12] = mbus_msg[4]; /* ToDo */
        playmsg_dirty = true;
    }
    else if (msg_size ==8 && mbus_msg[0] == 1 && mbus_msg[1] == 1 && mbus_msg[2] == 3)
    {   /* changing */
        gEmu.time = 0; /* reset playtime */
        playmsg_dirty = true;
        if (mbus_msg[3] == 0)
        {   /* changing track */
            if (mbus_msg[4] == 0xA && mbus_msg[5] == 0x3)
            {    /* next random */
                gEmu.playmsg[3] = rb->rand() % 10; /* ToDo */
                gEmu.playmsg[4] = rb->rand() % 10;
            }
            else if  (mbus_msg[4] == 0xB && mbus_msg[5] == 0x3)
            {   /* previous random */
                gEmu.playmsg[3] = rb->rand() % 10; /* ToDo */
                gEmu.playmsg[4] = rb->rand() % 10;
            }
            else
            {   /* normal track select */
                set_track(mbus_msg[4]*10 + mbus_msg[5]);
            }
        }
        else
        {   /* changing disk */
            diskmsg_dirty = true;
            gEmu.changemsg[3] = mbus_msg[3]; /* copy disk */
            gEmu.diskmsg[2] = mbus_msg[3];
            gEmu.changemsg[7] = gEmu.playmsg[11]; /* copy flags from status */
            gEmu.changemsg[8] = gEmu.playmsg[12];
            /*gEmu.playmsg[3] = 0; */  /* reset to track 1 */
            /*gEmu.playmsg[4] = 1; */
            mbus_send(gEmu.changemsg, sizeof(gEmu.changemsg));
        }
    }
    else
    {   /* if in doubt, send Ack */
        mbus_send("\x09\x0F\x00\x00\x00\x00\x00", 7);
    }

    if (playmsg_dirty)
    {
        rb->yield(); /* give the audio thread a chance to process */
        get_playmsg(); /* force update */
        mbus_send(gEmu.playmsg, sizeof(gEmu.playmsg));
    }

    if (diskmsg_dirty)
    {
        get_diskmsg(); /* force update */
        mbus_send(gEmu.diskmsg, sizeof(gEmu.diskmsg));
    }
}


/* called each second in case the emulator has something to do */
void emu_tick(void)
{
    get_playmsg(); /* force update */
    if (bit_test(gEmu.playmsg, 56)) /* play bit */
    {
        unsigned remain; /* helper as we walk down the digits */
        
        switch(gEmu.set_state)
        {
        case EMU_FF:
            gEmu.time += 10;
        case EMU_FR:
            gEmu.time -= 5;

            if (gEmu.time < 0)
                gEmu.time = 0;
            else if (gEmu.time > get_tracklength())
                gEmu.time = get_tracklength();
        
            /* convert value to MM:SS */
            remain = (unsigned)gEmu.time;
            gEmu.playmsg[7] = remain / (10*60);
            remain -= gEmu.playmsg[7] * (10*60);
            gEmu.playmsg[8] = remain / 60;
            remain -= gEmu.playmsg[8] * 60;
            gEmu.playmsg[9] = remain / 10;
            remain -= gEmu.playmsg[9] * 10;
            gEmu.playmsg[10] = remain;
        }

        mbus_send(gEmu.playmsg, sizeof(gEmu.playmsg));
    }
}


/****************** communication with Rockbox playback ******************/


/* update the play message with Rockbox info */
void get_playmsg(void)
{
    int track, time;

    if (gEmu.set_state != EMU_FF && gEmu.set_state != EMU_FR)
    {
        switch(rb->audio_status())
        {
        case AUDIO_STATUS_PLAY:
            print_scroll("AudioStat Play");
            if (gEmu.set_state == EMU_FF || gEmu.set_state == EMU_FR)
                gEmu.playmsg[2] = gEmu.set_state; /* set FF/FR */
            else
                gEmu.playmsg[2] = EMU_PLAYING; /* set normal play */

            bit_set(gEmu.playmsg, 56, true); /* set play */
            bit_set(gEmu.playmsg, 57, false); /* clear pause */
            bit_set(gEmu.playmsg, 59, false); /* clear stop */
            break;

        case AUDIO_STATUS_PLAY | AUDIO_STATUS_PAUSE:
            print_scroll("AudioStat Pause");
            gEmu.playmsg[2] = EMU_PAUSED;
            bit_set(gEmu.playmsg, 56, false); /* clear play */
            bit_set(gEmu.playmsg, 57, true); /* set pause */
            bit_set(gEmu.playmsg, 59, false); /* clear stop */
            break;

        default:
            print_scroll("AudioStat 0");
            gEmu.playmsg[2] = EMU_STOPPED;
            bit_set(gEmu.playmsg, 56, false); /* clear play */
            bit_set(gEmu.playmsg, 57, false); /* clear pause */
            bit_set(gEmu.playmsg, 59, true); /* set stop */
            break;
        }

        /* convert value to MM:SS */
        time = get_playtime();
        gEmu.time = time; /* copy it */
        gEmu.playmsg[7] = time / (10*60);
        time -= gEmu.playmsg[7] * (10*60);
        gEmu.playmsg[8] = time / 60;
        time -= gEmu.playmsg[8] * 60;
        gEmu.playmsg[9] = time / 10;
        time -= gEmu.playmsg[9] * 10;
        gEmu.playmsg[10] = time;
    }
    else /* FF/FR */
    {
        gEmu.playmsg[2] = gEmu.set_state; /* in FF/FR, report that instead */
    }

    track = get_track();
    gEmu.playmsg[3] = track / 10;
    gEmu.playmsg[4] = track % 10;
}

/* update the disk status message with Rockbox info */
void get_diskmsg(void)
{
    int tracks = rb->playlist_amount();
    if (tracks > 99)
        tracks = 99;
    gEmu.diskmsg[5] = tracks / 10;
    gEmu.diskmsg[6] = tracks % 10;
}

/* return the current track time in seconds */
int get_playtime(void)
{
    struct mp3entry* p_mp3entry;

    p_mp3entry = rb->audio_current_track();
    if (p_mp3entry == NULL)
        return 0;

    return p_mp3entry->elapsed / 1000;
}

/* return the total length of the current track */
int get_tracklength(void)
{
    struct mp3entry* p_mp3entry;

    p_mp3entry = rb->audio_current_track();
    if (p_mp3entry == NULL)
        return 0;

    return p_mp3entry->length / 1000;
}

/* change to a new track */
void set_track(int selected)
{
    if (selected > get_track())
    {
        print_scroll("audio_next");
        rb->audio_next();
    }
    else if (selected < get_track())
    {
        print_scroll("audio_prev");
        rb->audio_prev();
    }
}

/* return the track number */
int get_track(void)
{
    struct mp3entry* p_mp3entry;

    p_mp3entry = rb->audio_current_track();
    if (p_mp3entry == NULL)
        return 0;

    return p_mp3entry->index + 1; /* track numbers start with 1 */
}

/* start or resume playback */
void set_play(void)
{
    if (rb->audio_status() == AUDIO_STATUS_PLAY)
        return;

    if (rb->audio_status() == (AUDIO_STATUS_PLAY | AUDIO_STATUS_PAUSE))
    {
        print_scroll("audio_resume");
        rb->audio_resume();
    }
    else
    {
        print_scroll("audio_play(0, 0)");
        rb->audio_play(0, 0);
    }
}

/* pause playback */
void set_pause(void)
{
    if (rb->audio_status() == AUDIO_STATUS_PLAY)
    {
        print_scroll("audio_pause");
        rb->audio_pause();
    }
}

/* stop playback */
void set_stop(void)
{
    if (rb->audio_status() & AUDIO_STATUS_PLAY)
    {
        print_scroll("audio_stop");
        rb->audio_stop();
    }
}

/* seek */
void set_position(int seconds)
{
    if (rb->audio_status() & AUDIO_STATUS_PLAY)
    {
        print_scroll("audio_ff_rewind");
        rb->audio_ff_rewind(seconds * 1000);
    }
}

/****************** main thread + helper ******************/

/* set to everything flat and 0 dB volume */
void sound_neutral(void)
{    /* neutral sound settings */
    rb->sound_set(SOUND_BASS, 0);
    rb->sound_set(SOUND_TREBLE, 0);
    rb->sound_set(SOUND_BALANCE, 0);
    rb->sound_set(SOUND_VOLUME, 0);
#if (CONFIG_CODEC == MAS3587F) || (CONFIG_CODEC == MAS3539F)
    rb->sound_set(SOUND_LOUDNESS, 0);
    rb->sound_set(SOUND_SUPERBASS, 0);
    rb->sound_set(SOUND_AVC, 0);
#endif
}

/* return to user settings */
void sound_normal(void)
{   /* restore sound settings */
    rb->sound_set(SOUND_BASS, rb->global_settings->bass);
    rb->sound_set(SOUND_TREBLE, rb->global_settings->treble);
    rb->sound_set(SOUND_BALANCE, rb->global_settings->balance);
    rb->sound_set(SOUND_VOLUME, rb->global_settings->volume);
#if (CONFIG_CODEC == MAS3587F) || (CONFIG_CODEC == MAS3539F)
    rb->sound_set(SOUND_LOUDNESS, rb->global_settings->loudness);
    rb->sound_set(SOUND_SUPERBASS, rb->global_settings->superbass);
    rb->sound_set(SOUND_AVC, rb->global_settings->avc);
#endif
}

/* the thread running it all */
void thread(void)
{
    int msg_size;
    unsigned char mbus_msg[MBUS_MAX_SIZE];
    char buf[32];
    bool connected = false;
    long last_tick = *rb->current_tick; /* for 1 sec tick */

    do
    {
        msg_size = mbus_receive(mbus_msg, sizeof(mbus_msg), 1);
        if (msg_size > 0)
        {   /* received something */
            if(gTread.foreground)
            {
                dump_packet(buf, sizeof(buf), mbus_msg, msg_size);
                /*print_scroll(buf); */
            }
            if (msg_size > 2 && mbus_msg[0] == 1 
                && mbus_msg[msg_size-1] == calc_checksum(mbus_msg, msg_size-1))
            {   /* sanity and checksum OK */
                if (!connected)
                {   /* with the first received packet: */
                    sound_neutral(); /* set to flat and 0dB volume */
                    connected = true;
                }
                emu_process_packet(mbus_msg, msg_size-1); /* pass without chksum */
            }
            else if(gTread.foreground)
            {   /* not OK */
                print_scroll("bad packet");
            }
        }
        else if (msg_size < 0 && gTread.foreground)
        {   /* error */
            rb->snprintf(buf, sizeof(buf), "rcv error %d", msg_size);
            print_scroll(buf);
        }

        if (*rb->current_tick - last_tick >= gEmu.poll_interval)
        {   /* call the emulation regulary */
            emu_tick();
            last_tick += gEmu.poll_interval;
        }

    } while (!gTread.exiting);
}

/* callback to end the TSR plugin, called before a new one gets loaded */
static bool exit_tsr(bool reenter)
{
    if (reenter)
        return false; /* dont let it start again */
    gTread.exiting = true; /* tell the thread to end */
    rb->thread_wait(gTread.thread);  /* wait until it did */

    uart_init(BAUDRATE); /* return to standard baudrate */
    IPRE = (IPRE & ~0xF000); /* UART interrupt off */
    timer_set_mode(TM_OFF); /* timer interrupt off */

    sound_normal(); /* restore sound settings */
    return true;
}

/****************** main ******************/


int main(const void* parameter)
{
    (void)parameter;
#ifdef DEBUG
    int button;
#endif
    size_t buf_size;
    ssize_t stacksize;
    void* stack;

    mbus_init(); /* init the M-Bus layer */
    emu_init(); /* init emulator */

    rb->splash(HZ/5, "Alpine CDC"); /* be quick on autostart */

#ifdef DEBUG
    print_scroll("Alpine M-Bus Test");
    print_scroll("any key to TSR");
#endif

    /* init the worker thread */
    stack = rb->plugin_get_buffer(&buf_size); /* use the rest as stack */
    stacksize = buf_size;
    stack = (void*)(((unsigned int)stack + 100) & ~3); /* a bit away, 32 bit align */
    stacksize = (stacksize - 100) & ~3;
    if (stacksize < DEFAULT_STACK_SIZE)
    {
        rb->splash(HZ*2, "Out of memory");
        return -1;
    }

    rb->memset(&gTread, 0, sizeof(gTread));
    gTread.foreground = true;
    gTread.thread = rb->create_thread(thread, stack, stacksize, 0, "CDC"
                                      IF_PRIO(, PRIORITY_BACKGROUND)
                                      IF_COP(, CPU));

#ifdef DEBUG
    do
    {
        button = rb->button_get(true);
    } while (button & BUTTON_REL);
#endif

    gTread.foreground = false; /* we're in the background now */
    rb->plugin_tsr(exit_tsr); /* stay resident */
    
#ifdef DEBUG
    return rb->default_event_handler(button);
#else
    return 0;
#endif
}


/***************** Plugin Entry Point *****************/


enum plugin_status plugin_start(const void* parameter)
{
    /* now go ahead and have fun! */
    return (main(parameter)==0) ? PLUGIN_OK : PLUGIN_ERROR;
}