%import textio %import floats %option no_sysinit %zeropage basicsafe ; ; IMA ADPCM decoding and playback example. ; https://wiki.multimedia.cx/index.php/IMA_ADPCM ; https://wiki.multimedia.cx/index.php/Microsoft_IMA_ADPCM ; ; IMA ADPCM encodes two 16-bit PCM audio samples in 1 byte (1 word per nibble) ; thus compressing the audio data by a factor of 4. ; The encoding precision is about 13 bits per sample so it's a lossy compression scheme. ; ; NOTE: this program requires 16 bits MONO audio, and 256 byte encoded block size! ; HOW TO CREATE SUCH IMA-ADPCM ENCODED AUDIO? Use sox or ffmpeg: ; $ sox --guard source.mp3 -r 8000 -c 1 -e ima-adpcm out.wav trim 01:27.50 00:09 ; $ ffmpeg -i source.mp3 -ss 00:01:27.50 -to 00:01:36.50 -ar 8000 -ac 1 -c:a adpcm_ima_wav -block_size 256 -map_metadata -1 -bitexact out.wav ; Or use a tool such as https://github.com/dbry/adpcm-xq . ; main { ubyte adpcm_blocks_left uword @requirezp nibblesptr sub start() { wavfile.parse() txt.print_uw(wavfile.adpcm_size) txt.print(" adpcm data size = ") txt.print_ub(wavfile.num_adpcm_blocks) txt.print(" blocks\nsamplerate = ") txt.print_uw(wavfile.sample_rate) txt.print(" vera rate = ") txt.print_uw(wavfile.vera_rate_hz) txt.print("\n(b)enchmark or (p)layback? ") when c64.CHRIN() { 'b' -> benchmark() 'p' -> playback() } } sub benchmark() { nibblesptr = wavfile.adpcm_data_ptr txt.print("\ndecoding all blocks...\n") c64.SETTIM(0,0,0) repeat wavfile.num_adpcm_blocks { adpcm.init(peekw(nibblesptr), @(nibblesptr+2)) nibblesptr += 4 repeat 252 { ubyte @zp nibble = @(nibblesptr) adpcm.decode_nibble(nibble & 15) ; first word adpcm.decode_nibble(nibble>>4) ; second word nibblesptr++ } } float duration_secs = (c64.RDTIM16() as float) / 60.0 float words_per_second = 505.0 * (wavfile.num_adpcm_blocks as float) / duration_secs txt.print_uw(words_per_second as uword) txt.print(" words/sec\n") } sub playback() { nibblesptr = wavfile.adpcm_data_ptr adpcm_blocks_left = wavfile.num_adpcm_blocks cx16.VERA_AUDIO_CTRL = %10101111 ; mono 16 bit cx16.VERA_AUDIO_RATE = 0 ; halt playback repeat 1024 { cx16.VERA_AUDIO_DATA = 0 } sys.set_irqd() cx16.CINV = &irq_handler cx16.VERA_IEN = %00001000 ; enable AFLOW sys.clear_irqd() cx16.VERA_AUDIO_RATE = wavfile.vera_rate ; start playback txt.print("\naudio via irq\n") repeat { ; audio will play via the IRQ. } ; not reached: ; cx16.VERA_AUDIO_CTRL = %00100000 ; cx16.VERA_AUDIO_RATE = 0 ; txt.print("audio off.\n") } sub irq_handler() { if cx16.VERA_ISR & %00001000 { ; AFLOW irq. ;; cx16.vpoke(1,$fa0c, $a0) ; paint a screen color ; refill the fifo buffer with two decoded adpcm blocks (252 nibbles -> 1008 bytes per block) repeat 2 { adpcm.init(peekw(nibblesptr), @(nibblesptr+2)) nibblesptr += 4 repeat 252 { ubyte @zp nibble = @(nibblesptr) adpcm.decode_nibble(nibble & 15) ; first word cx16.VERA_AUDIO_DATA = lsb(adpcm.predict) cx16.VERA_AUDIO_DATA = msb(adpcm.predict) adpcm.decode_nibble(nibble>>4) ; second word cx16.VERA_AUDIO_DATA = lsb(adpcm.predict) cx16.VERA_AUDIO_DATA = msb(adpcm.predict) nibblesptr++ } adpcm_blocks_left-- if adpcm_blocks_left==0 { ; restart adpcm data from the beginning nibblesptr = wavfile.adpcm_data_ptr adpcm_blocks_left = wavfile.num_adpcm_blocks } } } else { ; TODO not AFLOW, handle other IRQ } ;; cx16.vpoke(1,$fa0c, 0) ; back to other screen color %asm {{ ply plx pla rti }} } } adpcm { ; IMA ADPCM decoder. ; https://wiki.multimedia.cx/index.php/IMA_ADPCM ; https://wiki.multimedia.cx/index.php/Microsoft_IMA_ADPCM ubyte[] t_index = [ -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8] uword[] t_step = [ 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 19, 21, 23, 25, 28, 31, 34, 37, 41, 45, 50, 55, 60, 66, 73, 80, 88, 97, 107, 118, 130, 143, 157, 173, 190, 209, 230, 253, 279, 307, 337, 371, 408, 449, 494, 544, 598, 658, 724, 796, 876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899, 15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767] uword @zp predict ubyte @zp index uword @zp pstep sub init(uword startPredict, ubyte startIndex) { predict = startPredict index = startIndex pstep = t_step[index] } sub decode_nibble(ubyte nibble) { ; this is the hotspot of the decoder algorithm! cx16.r0s = 0 ; difference if nibble & %0100 cx16.r0s += pstep pstep >>= 1 if nibble & %0010 cx16.r0s += pstep pstep >>= 1 if nibble & %0001 cx16.r0s += pstep pstep >>= 1 cx16.r0s += pstep if nibble & %1000 cx16.r0s = -cx16.r0s predict += cx16.r0s as uword index += t_index[nibble] if index & 128 index = 0 else if index > len(t_step)-1 index = len(t_step)-1 pstep = t_step[index] } } wavfile { const ubyte WAVE_FORMAT_PCM = $1 const ubyte WAVE_FORMAT_ADPCM = $2 const ubyte WAVE_FORMAT_IEEE_FLOAT = $3 const ubyte WAVE_FORMAT_ALAW = $6 const ubyte WAVE_FORMAT_MULAW = $7 const ubyte WAVE_FORMAT_DVI_ADPCM = $11 uword sample_rate uword vera_rate_hz ubyte vera_rate uword adpcm_size uword adpcm_data_ptr ubyte num_adpcm_blocks sub parse() { ; "RIFF" , filesize (int32) , "WAVE", "fmt ", fmtsize (int32) ; we assume file sizes are <= 64Kb so don't have to worry about the upper 16 bits uword @zp header = &wavdata.wav_data if header[0]!=iso:'R' or header[1]!=iso:'I' or header[2]!=iso:'F' or header[3]!=iso:'F' or header[8]!=iso:'W' or header[9]!=iso:'A' or header[10]!=iso:'V' or header[11]!=iso:'E' or header[12]!=iso:'f' or header[13]!=iso:'m' or header[14]!=iso:'t' or header[15]!=iso:' ' { txt.print("not a valid wav file\n") sys.exit(1) } ; uword filesize = peekw(header+4) uword chunksize = peekw(header+16) uword wavefmt = peekw(header+20) uword nchannels = peekw(header+22) sample_rate = peekw(header+24) ; we assume sample rate <= 65535 so we can ignore the upper word uword block_align = peekw(header+32) if block_align!=256 or nchannels!=1 or wavefmt!=WAVE_FORMAT_DVI_ADPCM { txt.print("invalid wav specs\n") sys.exit(1) } ; skip chunks until we reach the 'data' chunk header += chunksize + 20 repeat { chunksize = peekw(header+4) ; assume chunk size never exceeds 64kb so ignore upper word if header[0]==iso:'d' and header[1]==iso:'a' and header[2]==iso:'t' and header[3]==iso:'a' break header += 8 + chunksize } adpcm_data_ptr = header + 8 adpcm_size = chunksize num_adpcm_blocks = (chunksize / 256) as ubyte ; NOTE: THE ADPCM DATA NEEDS TO BE ENCODED IN 256-byte BLOCKS ! const float vera_freq_factor = 25e6 / 65536.0 vera_rate = (sample_rate as float / vera_freq_factor) + 1.0 as ubyte vera_rate_hz = (vera_rate as float) * vera_freq_factor as uword } } wavdata { %option align_page wav_data: %asmbinary "adpcm-mono.wav" wav_data_end: }