Scott, regarding:

I don't think clock and cs are dependent on each other. They are both
just outputs of the master controller.

For example, if I pull cs from my gumstix and try some i/o, mosi and
clk don't change behavior.

they are not dependent in how OMAP 3530 works in hardware.

I think they are dependent in how the software works:

.modalias = "ads7846" in board-overo.c sends to init.d a test whether touchscreen 7846 is
mounted or not in hardware.

At the boot, the script init.d in /etc/ creates other scripts rc0.d, rc1.d,... based on whether
7846 is mounted.

If it is, the log of the boot file says so, in what bus (1,2,3,4), in what channel (0,1) and puts that Chip
Select to 0.

If it is not, the log of the boot file says so.

This is detection of SPI devices sitting on the SPI bus.

The 1278 detection fails here.

The 7846 detection works.

Once a SPI device is detected by boot on a bus, on a Chip Select, then the driver for that device
(here ads7846.c) runs (tests again for touchscreen presence, receives and transmits SPI messages).

Ion A. Beza.

On Thu, Feb 25, 2010 at 1:22 PM, Scott Ellis <scottellis.developer@gmail.com> wrote:
I don't think clock and cs are dependent on each other. They are both
just outputs of the master controller.

For example, if I pull cs from my gumstix and try some i/o, mosi and
clk don't change behavior. Same signal on the analyzer. Obviously
nothing coming back on miso since my device requires cs.

I think cs is purely for the slave's benefit. Unless maybe there is
some sort of clock-stretching behaviour the slave could do like I2C.
But even if that were so, I don't think the overo McSPI driver is
watching for that, just based on the test I just did.

I even put a constant high on the cs line going to the gum, not
connected to the slave device and the gumstix output didn't change.
Again no miso of course.
(Probably shouldn't have done that test ;-)


On 2/25/10, Tony Oxendahl <toxend@gmail.com> wrote:
> Scott,
>
> SPI would clock only when the Chip Select line for a peripheral is low.
>
> So, SPI would clock only when the Chip Select 0 line for ADS 1278 is low.
>
> Up until the "booting" word showing in the log file of the boot, CS0 = 0.
> It's seen like this with a Voltmeter.
> Detection of 1278 doesn't take place, according to messages in the log file
> of the boot.
> It should according to .modalias in board_overo.c.
>
> When a device is not detected on SPI 1 Chip Select 0, then on SPI 1, Chip
> Select becomes 1.
>
> In the log of the boot file, at the "remounting root fs" level, Chip Select
> is 1.
> After "remounting root fs", ads1278.c and omap2_mcspi.c are not executed
> because
> CS0 = 1.
>
> I am studying more your:
>
> SPI setup on module load using the
>> spi_alloc/spi_add functions. I think this is new kernel spi stuff.
>>
>>
> Ion A. Beza.
>
> On Thu, Feb 25, 2010 at 11:28 AM, Scott Ellis <
> scottellis.developer@gmail.com> wrote:
>

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