Reading ADC channels using Raspberry Pi SPI interface

I am trying to read ADC channel 0 using SPI bus on Raspberry Pi and constantly outputting a 0.
Not sure why it is not working.
EDIT: I added sleep and wake up functions to try to get out of automatic sleep mode. It still seems to be outputting only 0.
Here is my updated code:

#!/usr/bin/python
import time
import sys
import spidev
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
spi=spidev.SpiDev()
SCLK=23
CS=26
MISO=21
spi.open(0,1)
spi.max_speed_hz = 4000000
spi.mode = 0
buff = 0
LTC_CONFIG_SLEEP = 1
currentLTCconfig = None

def Sleep():
  currentLTCconfig |= 0x01
  spi.xfer(currentLTCconfig)
  spi.xfer(0)    

def wake():
  wasSleep = currentLTCconfig & bin(LTC_CONFIG_SLEEP)
  currentLTCconfig &= ~bin(LTC_CONFIG_SLEEP)
  spi.xfer(currentLTCconfig)
  spi.xfer(0)
  if(wasSleep):
      delay(70)

def readADC(clkPin,csPin,misoPin,currentLTCconfig):
  buff=spi.xfer2([currentLTCconfig])
  newbuff = spi.xfer2([0])
  for y in buff:
      buff[y]<<8
      buff[y] |= 0xFF & (newbuff[y]>> 4) 
  return buff

if __name__=='__main__':
  try:
      while True:
          currentLTCconfig = 0x80
          val=readADC(SCLK,CS,MISO,currentLTCconfig)
          volt=val
          print('ADC value', str(volt))
  except KeyboardInterrupt:
          GPIO.cleanup()
          spi.close()
          sys.exit(0)
  #########################