finally add my Alpine car CD changer emulator, although very few people may use it

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@5618 a1c6a512-1295-4272-9138-f99709370657

2 files changed, 1204 insertions, 0 deletions

diff --git a/apps/plugins/SOURCES b/apps/plugins/SOURCES
index 775e20e9ee..1948cf663e 100644
--- a/apps/plugins/SOURCES
+++ b/apps/plugins/SOURCES
@@ -54,3 +54,8 @@ euroconverter.c
 jackpot.c
 nim.c
 #endif /* #ifdef HAVE_LCD_CHARCELLS */
+
+#ifndef HAVE_MMC
+/* not for Ondio, has no remote control pin */
+alpine_cdc.c
+#endif
diff --git a/apps/plugins/alpine_cdc.c b/apps/plugins/alpine_cdc.c
new file mode 100644
index 0000000000..16ebf3950f
--- /dev/null
+++ b/apps/plugins/alpine_cdc.c
@@ -0,0 +1,1199 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ *
+ * Copyright (C) 2003 Jörg Hohensohn
+ *
+ * Alpine CD changer Project
+ * This is a feasibility study for Archos emulating an Alpine M-Bus CD changer.
+ * 
+ * Currently realized as a plugin, which can't control the mp3 playback.
+ * It "just" follows all radio commands and answers accordingly.
+ * 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.
+ *
+ * All files in this archive are subject to the GNU General Public License.
+ * See the file COPYING in the source tree root for full license agreement.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+/* Only build for (correct) target */
+#if !defined(SIMULATOR) && CONFIG_CPU==SH7034 && !defined(HAVE_MMC)
+
+#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 "plugin.h"
+#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(void* parameter); /* main loop */
+enum plugin_status plugin_start(struct plugin_api* api, 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 
+{
+    int id; /* ID of the thread */
+    bool foreground; /* set as long as we're owning the UI */
+    bool exiting; /* signal to the thread that we want to exit */
+    bool ended; /* response from the thread, that is has exited */
+} gTread;
+
+static struct plugin_api* rb; /* here is the global API struct pointer */
+
+
+/****************** implementation ******************/
+
+
+/* setup static timer registers and values */
+void timer_init(unsigned hz, unsigned to)
+{
+    rb->memset(&gTimer, 0, sizeof(gTimer));
+    
+    gTimer.transmit = FREQ / hz; /* time for bit transitions */
+    gTimer.timeout = 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->plugin_register_timer(gTimer.timeout, 11, timer4_isr);
+    }
+    else if (mode == TM_TRANSMIT)
+    {
+        rb->plugin_register_timer(gTimer.transmit, 14, timer4_isr);
+    }
+    else
+    {
+        rb->plugin_unregister_timer();
+    }
+}
+
+
+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->plugin_unregister_timer(); /* 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]);
+#ifndef HAVE_LCD_CHARCELLS
+    rb->lcd_update();
+#endif
+    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/4] & (0x01 << bit%4)) != 0;
+}
+
+
+void bit_set(unsigned char* buf, unsigned bit, bool val)
+{
+    if (val)
+        buf[bit/4] |= (0x01 << bit%4);
+    else
+        buf[bit/4] &= ~(0x01 << bit%4);
+}
+
+
+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 mpeg 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->mpeg_status())
+        {
+        case MPEG_STATUS_PLAY:
+            print_scroll("MpegStat 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 MPEG_STATUS_PLAY | MPEG_STATUS_PAUSE:
+            print_scroll("MpegStat 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("MpegStat 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->mpeg_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->mpeg_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("mpeg_next");
+        rb->mpeg_next();
+    }
+    else if (selected < get_track())
+    {
+        print_scroll("mpeg_prev");
+        rb->mpeg_prev();
+    }
+}
+
+/* return the track number */
+int get_track(void)
+{
+    struct mp3entry* p_mp3entry;
+
+    p_mp3entry = rb->mpeg_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->mpeg_status() == MPEG_STATUS_PLAY)
+        return;
+
+    if (rb->mpeg_status() == (MPEG_STATUS_PLAY | MPEG_STATUS_PAUSE))
+    {
+        print_scroll("mpeg_resume");
+        rb->mpeg_resume();
+    }
+    else
+    {
+        print_scroll("mpeg_play(0)");
+        rb->mpeg_play(0);
+    }
+}
+
+/* pause playback */
+void set_pause(void)
+{
+    if (rb->mpeg_status() == MPEG_STATUS_PLAY)
+    {
+        print_scroll("mpeg_pause");
+        rb->mpeg_pause();
+    }
+}
+
+/* stop playback */
+void set_stop(void)
+{
+    if (rb->mpeg_status() & MPEG_STATUS_PLAY)
+    {
+        print_scroll("mpeg_stop");
+        rb->mpeg_stop();
+    }
+}
+
+/* seek */
+void set_position(int seconds)
+{
+    if (rb->mpeg_status() & MPEG_STATUS_PLAY)
+    {
+        print_scroll("mpeg_ff_rewind");
+        rb->mpeg_ff_rewind(seconds * 1000);
+    }
+}
+
+/****************** main thread + helper ******************/
+
+/* set to everything flat and 0 dB volume */
+void sound_neutral(void)
+{    /* neutral sound settings */
+    rb->mpeg_sound_set(SOUND_BASS, 0);
+    rb->mpeg_sound_set(SOUND_TREBLE, 0);
+    rb->mpeg_sound_set(SOUND_BALANCE, 0);
+    rb->mpeg_sound_set(SOUND_VOLUME, 92); /* 0 dB */
+    rb->mpeg_sound_set(SOUND_LOUDNESS, 0);
+    rb->mpeg_sound_set(SOUND_SUPERBASS, 0);
+    rb->mpeg_sound_set(SOUND_AVC, 0);
+}
+
+/* return to user settings */
+void sound_normal(void)
+{   /* restore sound settings */
+    rb->mpeg_sound_set(SOUND_BASS, rb->global_settings->bass);
+    rb->mpeg_sound_set(SOUND_TREBLE, rb->global_settings->treble);
+    rb->mpeg_sound_set(SOUND_BALANCE, rb->global_settings->balance);
+    rb->mpeg_sound_set(SOUND_VOLUME, rb->global_settings->volume);
+    rb->mpeg_sound_set(SOUND_LOUDNESS, rb->global_settings->loudness);
+    rb->mpeg_sound_set(SOUND_SUPERBASS, rb->global_settings->superbass);
+    rb->mpeg_sound_set(SOUND_AVC, rb->global_settings->avc);
+}
+
+/* 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);
+
+    gTread.ended = true; /* acknowledge the exit */
+    rb->remove_thread(gTread.id); /* commit suicide */
+    rb->yield(); /* pass control to other threads, we won't return */
+}
+
+/* callback to end the TSR plugin, called before a new one gets loaded */
+void exit_tsr(void)
+{
+    gTread.exiting = true; /* tell the thread to end */
+    while (!gTread.ended) /* wait until it did */
+        rb->yield();
+
+    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 */
+}
+
+/****************** main ******************/
+
+
+int main(void* parameter)
+{
+    (void)parameter;
+    /*int button; */
+    int stacksize;
+    void* stack;
+
+    mbus_init(); /* init the M-Bus layer */
+    emu_init(); /* init emulator */
+
+    rb->splash(HZ/5, true, "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(&stacksize); /* use the rest as stack */
+    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, true, "Out of memory");
+        return -1;
+    }
+
+    rb->memset(&gTread, 0, sizeof(gTread));
+    gTread.foreground = true;
+    gTread.id = rb->create_thread(thread, stack, stacksize, "CDC");
+
+#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(struct plugin_api* api, void* parameter)
+{
+    /* this macro should be called as the first thing you do in the plugin.
+       it test that the api version and model the plugin was compiled for
+       matches the machine it is running on */
+    TEST_PLUGIN_API(api);
+    rb = api; /* copy to global api pointer */
+
+    /* now go ahead and have fun! */
+    return (main(parameter)==0) ? PLUGIN_OK : PLUGIN_ERROR;
+}
+
+#endif /* #ifndef SIMULATOR, etc. */