Re: [Xenomai-help] Analogy Differential Mode

[Alexis Berlemont <alexis.berlemont@domain.hid>]

Hi,

Wong Sheng Chao wrote:
> Hi all
> 
> I'm still trying to figure out how to configure my NI card to read voltage
> signal in Differential Mode rather than single ended. 
Sorry. I skipped your mail without subject.

>I had been reading
> the API and it seems that I need to create a structure and define it's
> member accordingly
> 
> struct a4l_channel {
> 	unsigned long flags; /*!< Channel flags to define the reference. */
> 	unsigned long nb_bits; /*!< Channel resolution. */
> };
> typedef struct a4l_channel a4l_chan_t;
> 
> with the member flags being one of the following,
> 
> A4L_CHAN_AREF_GROUND 0x1
> A4L_CHAN_AREF_COMMON 0x2
> A4L_CHAN_AREF_DIFF 0x4
> A4L_CHAN_AREF_OTHER 0x8
> 
> and in my case A4L_CHAN_AREF_DIFF
> 
> My question is which function should I use to send this structure to
> configure the reference mode and where? I'm thinking it should be between
> these two functions, but i'm still not sure how I can achieve this.
> 

You should send a command structure thanks to a4l_snd_command().

See http://www.xenomai.org/documentation/xenomai-2.5/html/api/index.html:

/* The channel descriptor table */
static unsigned int chans[MAX_NB_CHAN];

/* The command to send  */
a4l_cmd_t cmd = {
	.idx_subd = ID_SUBD,
	.flags = 0,
	.start_src = TRIG_NOW,
	.start_arg = 0,
	.scan_begin_src = TRIG_TIMER,
	.scan_begin_arg = 8000000,	/* in ns */
	.convert_src = TRIG_TIMER,
	.convert_arg = 500000,	/* in ns */
	.scan_end_src = TRIG_COUNT,
	.scan_end_arg = 0,
	.stop_src = TRIG_COUNT,
	.stop_arg = NB_SCAN,
	.nb_chan = 0,
	.chan_descs = chans,
};

for (i = 0; i < ...; i++)
    chans[0] = PACK(0, 0, AREF(AREF_DIFF))
                    |  |  |_reference flags
                    |  |_range number
                    |_channel number

By the way, I had a quick look into the pcimio driver and I am not
sure that the driver supports differential mode for your
card. According to the function ni_load_channelgain_list(), M series
boards are OK (which is not the case, I think) and 611x models.

If the card PCI_6034E support "diff" mode, the driver should be
updated. 

> a4l_open();
> 
> //configure differential mode here.
> 
> a4l_fill();
> 
> 
> My current setup is as follow
> Distribution: Ubuntu 10.04
> Linux kernel: 2.6.37.3
> adeos patch: 2.9-00
> xenomai: 2.5.6
> DAQ card: National Instruments PCI_6034E
> 
> Thanks
> Chao
> 
> 
> 
> 
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-- 
Alexis.