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As of 2016, RME discontinued its Fireface series, thus it's OK for us to focus on released firmwares to drive known units. As long as investigating Fireface 400 with Windows driver and comparing the result to FFADO implementation, I can see these firmwares have different register assignments. On the other hand, according to manuals of each models, features relevant to packet streaming seem to be common, because GUIs for these models have the same options. It's reasonable to assume an abstraction layer of protocols to communicate to each models. This commit adds the abstraction layer for the protocols. This layer includes some functions to operate common features of models in this series. In IEC 61883-1/6, the sequence of packet can transfer timing information to synchronize receivers to transmitters. Units of each node on IEEE 1394 bus can generate transmitter's timing clock by handling value of SYT field in CIP header with high-precision clock. For audio and music units on IEEE 1394 bus, this recovered clock is designed to used for sampling clock to capture/generate PCM frames on DSP/ADC/DAC. (Actually, in this world, there's no units to implement this specification as is, as long as I know). Fireface series doesn't use this mechanism. Besides, It doesn't use isochronous packet with CIP header. It uses internal crystal unit as its initial sampling clock. When detecting input signals which can be available for sampling clock (e.g. ADAT input), drivers can configure units to use the signals as source of sampling clock. When something goes wrong, e.g. frequency mismatching between the signal and configured value, units fallback to the other detected signals alternatively. When detecting no alternatives, internal crystal unit is used as source of sampling clock. On manual of Fireface 400, this mechanism is described as 'Autosync'. On the units, packet streaming is controlled by write transactions to certain registers. Format of the packet, e.g. the number of data channels in a data block, is also configured by the same manner. For this purpose, .begin_session and .finish_session is added. The remarkable point of this protocol is to allow drivers to configure arbitrary sampling transmission frequency; e.g. 12.345 Hz. As long as I know, there's no actual DAC/ADC chips which support this kind of capability. I think a pair of packet streaming layer and data block processing layer is isolated from sampling data processing layer in a point of governed clock. In short, between these parts, resampling layer exists. Actually, for Fireface 400, write transactions to 0x'0000'8010'051c has an effect to change sampling clock frequency with base frequencies (32.0/44.1/48.0 kHz) and its multipliers (x2/x4), regardless of sampling transmission frequency. For this reason, the abstraction layer doesn't handle parameters for sampling clock. Instead, each implementation of .begin_session is expected to configure sampling transmission frequency. For packet streaming layer, it's enough to get current selection of source signals for the sampling clock and its frequency. In the abstraction layer, when internal crystal is selected, drivers can sets arbitrary sampling frequency, else they should follow configured frequency. For this purpose, .get_clock is added. Drivers are allows to bank up data fetching from a pair of packet streaming/data block processing layer and sampling data processing layer. This feature seems to suppress noises at starting/stopping packet streaming. For this purpose, .switch_fetching_mode is added. As I described in the above, units have remarkable mechanism to manage sampling clock and process sampling data. For debugging purpose, .dump_sync_status and .dump_clock_config are added. I don't have a need to common interface to represent the status and configuration, developers can add actual implementation of the abstraction layer as they like. Unlike PCM frames, MIDI messages are transferred by asynchronous communication over IEEE 1394 bus, thus target addresses are important for this feature. The .midi_high_addr_reg, .midi_rx_port_0_reg and .midi_rx_port_1_reg are for this purpose. I'll describe them in following commit. Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Signed-off-by: Takashi Iwai <tiwai@suse.de> |
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