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We read the raw data from the disc, extract the Q sub-channel and decode the ISRC. This gives better results (no duplicate ISRCs) than using the read ISRC sub-channel command. Probably due to bad implementation on some drives / drivers.
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| Original file line number | Diff line number | Diff line change |
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| /* -------------------------------------------------------------------------- | ||
| MusicBrainz -- The Internet music metadatabase | ||
| Copyright (C) 2013 Johannes Dewender | ||
| This library is free software; you can redistribute it and/or | ||
| modify it under the terms of the GNU Lesser General Public | ||
| License as published by the Free Software Foundation; either | ||
| version 2.1 of the License, or (at your option) any later version. | ||
| This library is distributed in the hope that it will be useful, | ||
| but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| Lesser General Public License for more details. | ||
| You should have received a copy of the GNU Lesser General Public | ||
| License along with this library; if not, write to the Free Software | ||
| Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | ||
| --------------------------------------------------------------------------- */ | ||
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| #include <stdio.h> | ||
| #include <string.h> | ||
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| #include "discid/discid_private.h" | ||
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| /* Send a scsi command and receive data. */ | ||
| int scsi_cmd(int fd, unsigned char *cmd, int cmd_len, | ||
| const char *data, int data_len); | ||
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| static void decode_isrc(unsigned char *q_channel, char *isrc) { | ||
| int isrc_pos; | ||
| int data_pos; | ||
| int bit_pos; | ||
| int bit; | ||
| unsigned char buffer; | ||
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| isrc_pos = 0; | ||
| /* q_channel[0] = 0x03 -> mode 3 -> ISRC data */ | ||
| data_pos = 1; | ||
| bit_pos = 7; | ||
| buffer = 0; | ||
| /* first 5 chars of ISRC are alphanumeric and 6-bit BCD encoded */ | ||
| for (bit = 0; bit < 5*6; bit++) { | ||
| buffer = buffer << 1; | ||
| if ((q_channel[data_pos] & (1 << bit_pos)) == (1 << bit_pos)) { | ||
| buffer++; | ||
| } | ||
| bit_pos--; | ||
| if ((bit + 1)%8 == 0) { | ||
| bit_pos = 7; | ||
| data_pos++; | ||
| } | ||
| if ((bit + 1)%6 == 0) { | ||
| /* 0x3f = only lowest 6 bits set */ | ||
| isrc[isrc_pos] = '0' + (buffer & 0x3f); | ||
| isrc_pos++; | ||
| buffer = 0; | ||
| } | ||
| } | ||
| /* buffer[4] includes 2 zero bits | ||
| * last 7 chars of ISRC are only numeric and 4-bit encoded | ||
| */ | ||
| isrc[5] = '0' + (q_channel[5] >> 4); | ||
| isrc[6] = '0' + (q_channel[5] & 0x0f); | ||
| isrc[7] = '0' + (q_channel[6] >> 4); | ||
| isrc[8] = '0' + (q_channel[6] & 0x0f); | ||
| isrc[9] = '0' + (q_channel[7] >> 4); | ||
| isrc[10] = '0' + (q_channel[7] & 0x0f); | ||
| isrc[11] = '0' + (q_channel[8] >> 4); | ||
| /* q_channel[9] are zero bits | ||
| * q_channel 10-12 are AFRAME | ||
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| */ | ||
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| } | ||
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| void read_track_isrc_raw(int fd, mb_disc_private *disc, int track_num) { | ||
| /* there should be at least one ISRC in 100 sectors per spec | ||
| * We try 150 (= 2 seconds) to be sure, but break when successfull | ||
| */ | ||
| const int SEC_NUM = 150; | ||
| unsigned char cmd[12]; | ||
| unsigned char data[SEC_NUM*2448]; /* overall data */ | ||
| unsigned char q_buffer; | ||
| unsigned char q_data[12]; /* sub-channel data in 1 sector */ | ||
| char isrc[ISRC_STR_LENGTH+1]; | ||
| unsigned long offset; | ||
| int char_num; | ||
| int sector; | ||
| int i; | ||
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| memset(cmd, 0, sizeof cmd); | ||
| memset(data, 0, sizeof data); | ||
| memset(isrc, 0, sizeof isrc); | ||
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| offset = disc->track_offsets[track_num]; | ||
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| /* 0xbe = READ CD, implementation optional in contrast to 0x42 | ||
| * support given with GET CONFIGURATION (0x46) | ||
| * Support part of: | ||
| * Multi-Read Feature (0x001d) and | ||
| * CD Read Feature (0x001e), | ||
| */ | ||
| cmd[0] = 0xbe; /* READ CD */ | ||
| cmd[2] = offset >> 32; | ||
| cmd[3] = offset >> 16; | ||
| cmd[4] = offset >> 8; | ||
| cmd[5] = offset; /* from where to start reading */ | ||
| cmd[6] = SEC_NUM >> 16; | ||
| cmd[7] = SEC_NUM >> 8; | ||
| cmd[8] = SEC_NUM; /* sectors to read */ | ||
| cmd[9] = 0xF8; /* 11111000 sync=1 all-header=11 user=1, ecc=1 | ||
| * no-error=00 */ | ||
| cmd[10] = 0x01; /* Sub-Channel Selection raw P-W=001*/ | ||
| /* cmd[11] = control byte */ | ||
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| if (scsi_cmd(fd, cmd, sizeof cmd, data, sizeof data) != 0) { | ||
| fprintf(stderr, "Warning: Cannot get ISRC code for track %d\n", | ||
| track_num); | ||
| return; | ||
| } | ||
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| /* each sector has 96 bytes for one Q-channel type | ||
| * We try until we finde an ISRC Q-channel | ||
| */ | ||
| for (sector = 0; sector < SEC_NUM; sector++) { | ||
| char_num = 0; | ||
| memset(q_data, 0, sizeof q_data); | ||
| q_buffer = 0; | ||
| /* the first 2352 bytes are raw data without sub-channels | ||
| * We only want the 96 bit sub-channel data | ||
| */ | ||
| for (i = 2352; i < 2448; i++) { | ||
| q_buffer = q_buffer << 1; | ||
| /* the 6th bit is the Q-channel bit | ||
| * we want to collect these bits | ||
| */ | ||
| if ((data[i + (sector*2448)] & (1 << 6)) == (1 << 6)) { | ||
| q_buffer++; | ||
| } | ||
| if ((i+1)%8 == 0) { | ||
| /* we have gathered one complete byte */ | ||
| q_data[char_num] = q_buffer; | ||
| if (char_num == 0) { | ||
| /* test if we got the right type | ||
| * of q-channel (ADR = 0x03) | ||
| * upper 4 bit are CONTROL | ||
| * Go to next sector otherwise | ||
| */ | ||
| if ((q_buffer & 0x0F) != 0x03) { | ||
| break; | ||
| } | ||
| } | ||
| char_num++; | ||
| q_buffer = 0; | ||
| } | ||
| } | ||
| if ((q_data[0] & 0x0F) == 0x03) { | ||
| /* we found a Q-channel with ISRC data */ | ||
| decode_isrc(q_data, isrc); | ||
| break; | ||
| } | ||
| } | ||
| strncpy(disc->isrc[track_num], isrc, ISRC_STR_LENGTH); | ||
| } | ||
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| /* EOF */ | ||
I think I might be mistaken here. I found a SCSI-3 MMC draft which states there are 4 ZERO bits (which would be the rest of q_channel[8] and 8 bits AFRAME, which would be q_channel[9].
So q_channel 10-11 ar e the 16 CRC bits. and there is no q_channel[12]. (there are only 12 bytes).