Question on AUX ADC of AD9862

GNU Radio
1

Hi,

I want to read RSSI value using analog AUX ADC, I think we can read

RSSI
through AUX_ADC_A1 pin of AD9862, I looked through the code
of usrp_read_aux_adc in file
/root/gnuradio/gnuradio-3.1.3/usrp/host/lib/legacy/usrp_primes.cc,

bool
usrp_read_aux_adc (struct usb_dev_handle *udh, int slot,
int which_adc, int *value)
{
*value = 0;
int which_codec;
if (!slot_to_codec (slot, &which_codec))
return false;
if (!(0 <= which_codec && which_codec < 2)){
fprintf (stderr, “usrp_read_aux_adc: invalid adc = %d\n”,
which_adc);
return false;
}
unsigned char aux_adc_control =
AUX_ADC_CTRL_REFSEL_A // on chip reference
| AUX_ADC_CTRL_REFSEL_B; // on chip reference
int rd_reg = 26; // base address of two regs to read for result
// program the ADC mux bits
if (tx_slot_p (slot))
aux_adc_control |= AUX_ADC_CTRL_SELECT_A2 | AUX_ADC_CTRL_SELECT_B2;
else {
rd_reg += 2;
aux_adc_control |= AUX_ADC_CTRL_SELECT_A1 | AUX_ADC_CTRL_SELECT_B1;
}
// I’m not sure if we can set the mux and issue a start conversion
// in the same cycle, so let’s do them one at a time.
usrp_9862_write (udh, which_codec, 34, aux_adc_control);
if (which_adc == 0)
aux_adc_control |= AUX_ADC_CTRL_START_A;
else {
rd_reg += 4;
aux_adc_control |= AUX_ADC_CTRL_START_B;
}
// start the conversion
usrp_9862_write (udh, which_codec, 34, aux_adc_control);
// read the 10-bit result back
unsigned char v_lo = 0;
unsigned char v_hi = 0;
bool r = usrp_9862_read (udh, which_codec, rd_reg, &v_lo);
r &= usrp_9862_read (udh, which_codec, rd_reg + 1, &v_hi);

if ®
*value = ((v_hi << 2) | ((v_lo >> 6) & 0x3)) << 2; // format
as
12-bit
return r;
}

my question is:
1.The AD 9862 specification says: “The AUX SPI can be enabled and
configured
by setting register AUX ADC CTRL. Setting register use pins high enables
the
AUX SPI port.”, but in the above code AUX_ADC_CTRL_AUX_SPI was not set
high(
In my opinion, aux_adc_control should be added with | =
AUX_ADC_CTRL_AUX_SPI
because usrp_9862_write and usrp_9862_read all need SPI operation, so we
should enable AUX API), Is this a mistype or another method ?
2.stefan.bruens in the list had said that the low 16 bits is the RSSI
value,
I want to know why did the above code combine the high and low 16-bit
and
format the data into 12-bit ?
3. Even with the RSSI value (int type), what should I do to convert that
value into dBm unit ?

    Thanks.