[ts-7000] Confused about 7250 A/D

["naturalwatt" <>]

I am very confused about how the A/D works on the 7250. Reading the Linux 
Developers
Manual it talks about an a2d_driver.o, which is not present in the 
lib/modules/kernel
hierarchy nor in the source tree for ts11.

There is a helpful example here, the adc_7250 program, which works as 
advertised, using
direct memory access.

The description in the 7250 Manual, and the EP9301 User Guide, implies that you 
read in a
32 bit value and must blank off all but the lower twelve bits. (0xFFF).

The adc_7250 program masks off 16 bits, using 0xFFFF, and include logic like 
this:

if(avg < 0x7000)
avg = avg + 0x10000;

if(virgin == TRUE) //use approximation
{
avg = avg - 0x9E58;
val = ((double)avg * 3.3) / 0xC350;
}

I am getting raw values like this:
Voltage ; Decimal : hex
0.2V      : 40921 0x9fed
1.6V      : 248 0xf8
3.3V      : 25122 0x6222

The above C code converts the raw values, but I don't understand why. Surely 
the raw
values should go from 0x000 to 0xfff, from 0V to 3.3V?

What am I missing?

Thanks in advance,

Martin








 
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