summaryrefslogtreecommitdiffstats
path: root/apps/plugins/alpine_cdc.c
blob: 93d9418f6567c2b2990521e9bde8cdb61159eae4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
/***************************************************************************
 *             __________               __   ___.
 *   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;
}