On Thursday, April 07, 2016 9:48 AM, Hartley Sweeten wrote: > On Thursday, April 07, 2016 3:16 AM, Ian Abbott wrote: >> On 06/04/16 19:06, H Hartley Sweeten wrote: >>> The "hc" type boards have 64 analog input channels with a 64 entry queue. >>> All the others have 16 channels and a 256 entry queue. >>> >>> Currently the boardinfo 'qram_len' is used to initialize the subdevice >>> 'n_chan' and 'len_chanlist'. This works for the 64 channel boards but >>> sets the 'n_chan' wrong for the 16 channel boards. >> >> I think the 256 QRAM positions is to allow use with a set of EXP-1800 >> boards, each of which can multiplex one of the single-ended inputs of >> the DAS-1800 series into 16 channels. According to the user's guide, >> they can be daisy chained to provide up to 256 channels. >> >> Datasheet: >> >> http://www.tek.com/sites/tek.com/files/media/media/resources/exp-1800_ds.pdf >> >> User's Guide download page (need to fill in contact info!): >> >> http://www.tek.com/manual/exp-1800-users-guide-92160b-manual >> >> >> So it's probably best to leave the number of channels alone.
Finally able to get the user's guide to download. > The EXP-1800 support looks like it will need additional changes to the driver > in order to work correctly. According to the data sheet: > > 1) all board input channels must be configured as single-ended, > EXP-1800 inputs can be single-ended or differential. Not sure how > the board needs to be programmed to achieve this. > 2) only gains of 1 and 50 are selectable on a per-channel basis > 3) resolution is 12-bit, not clear how this works on a 16-bit board > 4) max ai speed depends on the EXP-1800 gain not the board > gain 1 = 312kHz sample rate > gain 50 = 150kHz sample rate > 5) gain must be the same on all channels and the boards gain must be 1 > > Additionally, it's not clear how the channel mapping works for each > EXP-1800 connected to a board input channel. The channel mapping is a bit warped as far as comedi is concerned. Each EXP-1800 is jumper configured for what board input channel will be used to return the 16 channels on the EXP-1800. The hi bits of the QRAM are output to the EXP-1800 boards to select the channel as the MUX4-7 pins on the connector. Channel mapping looks like this: On-board channel 0 EXP-1800 logical channels 0 to 15 On-board channel 1 EXP-1800 logical channels 16 to 31 ... On-board channel 15 EXP-1800 logical channels 240 to 255 So it looks like the QRAM 'channel' (i.e. the comedi channel) to physical channel mapping goes: channel 0 On-board channel 0 / EXP-1800 logical channel 0 channel 1 On-board channel 1 / EXP-1800 logical channel 16 channel 2 On-board channel 2 / EXP-1800 logical channel 32 channel 3 On-board channel 3 / EXP-1800 logical channel 48 channel 4 On-board channel 4 / EXP-1800 logical channel 64 channel 5 On-board channel 5 / EXP-1800 logical channel 80 channel 6 On-board channel 6 / EXP-1800 logical channel 96 channel 7 On-board channel 7 / EXP-1800 logical channel 112 channel 8 On-board channel 8 / EXP-1800 logical channel 128 channel 9 On-board channel 9 / EXP-1800 logical channel 144 channel 10 On-board channel 10 / EXP-1800 logical channel 160 channel 11 On-board channel 11 / EXP-1800 logical channel 176 channel 12 On-board channel 12 / EXP-1800 logical channel 192 channel 13 On-board channel 13 / EXP-1800 logical channel 208 channel 14 On-board channel 14 / EXP-1800 logical channel 224 channel 15 On-board channel 15 / EXP-1800 logical channel 240 channel 16 On-board channel 0 / EXP-1800 logical channel 1 channel 17 On-board channel 1 / EXP-1800 logical channel 17 ... channel 254 On-board channel 14 / EXP-1800 logical channel 239 channel 255 On-board channel 15 / EXP-1800 logical channel 255 So if no EXP-1800 boards are used the comedi channel matches the on-board channel. But, if any EXP-1800 boards are used the comedi channel to physical channel gets all screwy. Just using one EXP-1800 board connected to on-board channel 0 results in this comedi channel map for the 32 'usable' channels: channel 0 EXP-1800 logical channel 0 channel 1 On-board channel 1 channel 2 On-board channel 2 channel 3 On-board channel 3 channel 4 On-board channel 4 channel 5 On-board channel 5 channel 6 On-board channel 6 channel 7 On-board channel 7 channel 8 On-board channel 8 channel 9 On-board channel 9 channel 10 On-board channel 10 channel 11 On-board channel 11 channel 12 On-board channel 12 channel 13 On-board channel 13 channel 14 On-board channel 14 channel 15 On-board channel 15 channel 16 EXP-1800 logical channel 1 channel 32 EXP-1800 logical channel 2 channel 48 EXP-1800 logical channel 3 channel 64 EXP-1800 logical channel 4 channel 80 EXP-1800 logical channel 5 channel 96 EXP-1800 logical channel 6 channel 112 EXP-1800 logical channel 7 channel 128 EXP-1800 logical channel 8 channel 144 EXP-1800 logical channel 9 channel 160 EXP-1800 logical channel 10 channel 176 EXP-1800 logical channel 11 channel 192 EXP-1800 logical channel 12 channel 208 EXP-1800 logical channel 13 channel 224 EXP-1800 logical channel 14 channel 240 EXP-1800 logical channel 15 > I think it's better to set the number of channels to 16 and just support > the on-board analog inputs for now. Once the EXP-1800 support is > figured out it can be added. There is also the issue with the gain when using an EXP-1800 board. For now I think limiting the channels to 16 is the best option. Also, the driver doesn't state that the EXP-1800 boards are supported. I'm not sure the author (Frank Mori Hess) actually thought about or tested it when he originally wrote the driver. Regards, Hartley _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
