mirror of https://gitee.com/openkylin/linux.git
6fb7db902b
As long as investigating Fireface 400, format of payload of each isochronous packet is not IEC 61883-1/6, thus its format of data block is not AM824. The remarkable points of the format are: * The payload just consists of some data channels of quadlet size without CIP header. * Each data channels includes data aligned to little endian order. * One data channel consists of two parts; 8 bit ancillary field and 24 bit PCM frame. Due to lack of CIP headers, rx/tx packets include no CIP headers and different way to check packet discontinuity. For tx packet, the ancillary field is used for counter. However, the way of counting is different depending on positions of data channels. At 44.1 kHz, ancillary field in: * 1st/6th/9th/10th/14th/17th data channels: not used for this purpose. * 2nd/18th data channels: incremented every data block (0x00-0xff). * 3rd/4th/5th/11th/12th/13th data channels: incremented every 256 data blocks (0x00-0x07). * 7th/8th/15th/16th data channels: incremented per the number of data blocks in a packet. The increment can occur per packet (0x00-0xff). For tx packet, tag of each isochronous packet is used for this purpose. The value of tag cyclically changes between 0, 1, 2 and 3 in this order. The interval is different depending on sampling transmission frequency. At 44.1/48.0 kHz, it's 256 data blocks. At 88.2 kHz, it's 96 data blocks. The number of data blocks in tx packet is exactly the same as SYT_INTERVAL. There's no empty packet or no-data packet, thus the throughput is not 8,000 packets per sec. On the other hand, the one in rx packet is 8,000 packets per sec, thus the number of data blocks is different between each packet, depending on sampling transmission frequency: * 44.1 kHz: 5 or 6 * 48.0 kHz: 5 or 6 or 7 * 88.2 kHz: 10 or 11 or 12 This commit adds data processing layer to satisfy the above specification in a policy of 'best effort'. Although PCM frames are handled for intermediate buffer to user space, the ancillary data is not handled at all to reduce CPU usage, thus counter is not checked. 0 is always used for tag of isochronous packet. Furthermore, the packet streaming layer is responsible for calculation of the number of data blocks for each packet, thus it's not exactly the same sequence from the above observation. Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Signed-off-by: Takashi Iwai <tiwai@suse.de> |
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| .. | ||
| Makefile | ||
| amdtp-ff.c | ||
| ff-midi.c | ||
| ff-proc.c | ||
| ff-transaction.c | ||
| ff.c | ||
| ff.h | ||