cee.py

import usb.core

MODE_DISABLED=0
MODE_SVMI=1
MODE_SIMV=2
gainMapping = {1:0x00<<2, 2:0x01<<2, 4:0x02<<2, 8:0x03<<2, 16:0x04<<2, 32:0x05<<2, 64:0x06<<2, .5:0x07<<2}
chanMapping = {0:'a_i', 1:'a_v', 2:'b_v', 3:'b_i'}

def unpackSign(n):
	return n - (1<<12) if n>2048 else n

class CEE(object):
	def __init__(self):
		self.dev = usb.core.find(idVendor=0x9999, idProduct=0xffff)
		self.gains = 4*[1]
		self.setGain(0, 1) # set all gains to 1 
		self.setGain(1, 1)
		self.setGain(2, 1)
		self.setGain(3, 1)
		if not self.dev:
			raise IOError("device not found")
			
	def b12unpack(self, s):
		"Turn a 3-byte string containing 2 12-bit values into two ints"
		return s[0]|((s[1]&0x0f)<<8), ((s[1]&0xf0) >> 4)|(s[2]<<4)

	def readADC(self):
		data = self.dev.ctrl_transfer(0x40|0x80, 0xA0, 0, 0, 6)
		l = self.b12unpack(data[0:3]) + self.b12unpack(data[3:6])
		vals = map(unpackSign, l)
		return {
			'a_v': vals[0]/2048.0*5/self.gains[1],
			'a_i': ((vals[1]/2048.0*2.5))/45/.07/self.gains[0],
			'b_v': vals[2]/2048.0*5/self.gains[2],
			'b_i': ((vals[3]/2048.0*2.5))/45/.07/self.gains[3],
		}

	def set(self, chan, v=None, i=None):
		"""v is voltage in volts, i is current in amps"""
		cmd = 0xAA+chan
		if v is not None:
			dacval = int(round(v/5.0*4095))
			self.dev.ctrl_transfer(0x40|0x80, cmd, dacval, MODE_SVMI, 0)
		elif i is not None:
			dacval = int((2**12*(1.25+(45*.07*i)))/2.5)
			self.dev.ctrl_transfer(0x40|0x80, cmd, dacval, MODE_SIMV, 0)
		else:
			self.dev.ctrl_transfer(0x40|0x80, cmd, 0, MODE_DISABLED, 0)	

	def setGain(self, ADCChan, gain):
		"""ADCChan is a number between 0 and 3 corresponding 'chanMapping' or the on-hardware ADC mappings"""
		self.gains[ADCChan] = gain
		self.dev.ctrl_transfer(0x40|0x80, 0x65, gainMapping[gain], ADCChan, 0)

	def setA(self, v=None, i=None):
		self.set(0, v, i)
	
	def setB(self, v=None, i=None):
		self.set(1, v, i)

	def bootload(self):
		self.dev.ctrl_transfer(0x40|0x80, 0xBB, 0, 0, 1)

if __name__ == "__main__":
	cee = CEE()