XADC Wizard - Reading analog inputs

[carlos-e-teixeira]

Hi Mr. Pavel, I'm trying now to read some analog values using the IP XADC Wizard. For hardware configuration, I used the TCL code you implemented.

cell xilinx.com:ip:xadc_wiz:3.3 xadc_0 {
  DCLK_FREQUENCY 143
  ADC_CONVERSION_RATE 100
  XADC_STARUP_SELECTION independent_adc
  CHANNEL_ENABLE_VAUXP0_VAUXN0 true
  CHANNEL_ENABLE_VAUXP1_VAUXN1 true
  CHANNEL_ENABLE_VAUXP8_VAUXN8 true
  CHANNEL_ENABLE_VAUXP9_VAUXN9 true
  CHANNEL_ENABLE_VP_VN true
} {
  Vp_Vn Vp_Vn
  Vaux0 Vaux0
  Vaux1 Vaux1
  Vaux8 Vaux8
  Vaux9 Vaux9
}

apply_bd_automation -rule xilinx.com:bd_rule:axi4 -config {
  Master /ps_0/M_AXI_GP0
  Clk Auto
} [get_bd_intf_pins xadc_0/s_axi_lite]

set_property RANGE 64K [get_bd_addr_segs ps_0/Data/SEG_xadc_0_Reg]
set_property OFFSET 0x40020000 [get_bd_addr_segs ps_0/Data/SEG_xadc_0_Reg]

For my C application, I declared a volatile pointer and the memory mapping of this pointer is also according to your code ('sdr-transceiver-hpsdr.c') and hardware addressing.

volatile int32_t *xadc;
xadc = mmap(NULL, 16*sysconf(_SC_PAGESIZE), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x40020000);

From now on, I'm not sure about the next steps (pieces of code) to be implemented in order to get 4 analog values corresponding to the 4 slow analog inputs available on the connector E2 of the Red Pitaya.

I did not understand what you've implemented. I know the XADC block only converts analog values to digital vectors of 12 bits, doesn't it?

Also, I know the XADC block accepts bipolar analog voltages (-0.5V to +0.5V) and unipolar analog voltages (0V to +1V). Since I'm using the temperature sensor LM35, I think I will not have any problem to read it.

I appreciate again in advance your help! Thank you so much! Best regards!

[pavel-demin]

Please, don't call me Mr Pavel.

The only program where I'm using the XADC block is sdr-transceiver-hpsdr.c. I'm reading the data with the following code:

int32_t value;
value = xadc[144] >> 3;
value = xadc[145] >> 3;
value = xadc[152] >> 3;
value = xadc[153] >> 3;

The addresses are from the XADC Wizard documentation (PG091, page 18).

[carlos-e-teixeira]

Sorry Pavel, I was trying to be courteous.

So... I totally understand now, but just one more question. Why do you use a right-shift operation of 3 positions? Would not it be a right-shift operation of 4 positions, since we have 16-bits registers that keep the 12-bit MSB justified result of A/D conversion on the corresponding auxiliary analog input.

Thank you again, Pavel! You help me a lot! Best regards!

[pavel-demin]

Why do you use a right-shift operation of 3 positions? Would not it be a right-shift operation of 4 positions, since we have 16-bits registers that keep the 12-bit MSB justified result of A/D conversion on the corresponding auxiliary analog input.

You're right. The right-shift by 4 is the most correct way to process the XADC data.

However, in my program I was looking for a way to obtain 12-bit values for the unipolar analog voltages and the right-shift by 3 worked well enough.