import smbus

WHICH_BUS = 0 # RPi Rev1 board

ADDR = 0x5a # default MPR121 address (of 4 possible)

# MPR121 registers
MHD_R = 0x2b
NHD_R = 0x2c
NCL_R = 0x2d
FDL_R = 0x2e

MHD_F = 0x2f
NHD_F = 0x30
NCL_F = 0x31
FDL_F = 0x32

ELE0_T = 0x41
ELE0_R = 0x42
ELE1_T = 0x43
ELE1_R = 0x44
ELE2_T = 0x45
ELE2_R = 0x46
ELE3_T = 0x47
ELE3_R = 0x48
ELE4_T = 0x49
ELE4_R = 0x4a
ELE5_T = 0x4b
ELE5_R = 0x4c
ELE6_T = 0x4d
ELE6_R = 0x4e
ELE7_T = 0x4f
ELE7_R = 0x50
ELE8_T = 0x51
ELE8_R = 0x52
ELE9_T = 0x53
ELE9_R = 0x54
ELE10_T = 0x55
ELE10_R = 0x56
ELE11_T = 0x57
ELE11_R = 0x58

AFE1 = 0x5c
AFE2 = 0x5d
ECR = 0x5e

GPIO_CTL0 = 0x73
GPIO_CTL1 = 0x74
GPIO_DAT = 0x75
GPIO_DIR = 0x76
GPIO_EN = 0x77
GPIO_SET = 0x78
GPIO_CLR = 0x79
GPIO_TOG = 0x7a

AUTO_CFG0 = 0x7b
AUTO_CFG1 = 0x7c
AUTO_USL = 0x7d
AUTO_LSL = 0x7e
AUTO_TL = 0x7f


class MPR121(object):
    def __init__(self, which, addr=ADDR):
        self.bus = smbus.SMBus(which)
        self.addr = addr

    def write(self, reg, value):
        self.bus.write_byte_data(self.addr, reg, value)

    def read(self, reg):
        ### this doesn't work on MPR121. requires a REPEATED START.
        return self.bus.read_byte_data(self.addr, reg)

    def config(self):
        # ensure the MPR121 is in Stop Mode
        self.write(ECR, 0x00)

        self.write(MHD_R, 0x01)
        self.write(NHD_R, 0x01)
        self.write(NCL_R, 0x00)
        self.write(FDL_R, 0x00)

        self.write(MHD_F, 0x01)
        self.write(NHD_F, 0x01)
        self.write(NCL_F, 0xff)
        self.write(FDL_F, 0x02)

        self.write(ELE0_T, 0x0f)
        self.write(ELE0_R, 0x0a)
        self.write(ELE1_T, 0x0f)
        self.write(ELE1_R, 0x0a)
        self.write(ELE2_T, 0x0f)
        self.write(ELE2_R, 0x0a)
        self.write(ELE3_T, 0x0f)
        self.write(ELE3_R, 0x0a)
        self.write(ELE4_T, 0x0f)
        self.write(ELE4_R, 0x0a)
        self.write(ELE5_T, 0x0f)
        self.write(ELE5_R, 0x0a)

        self.write(AFE2, 0x04)

        # enable ELE11 as CMOS output, set to GND, then enable it
        self.write(GPIO_CTL0, 0x00) # CTL0
        self.write(GPIO_CTL1, 0x00) # CTL1

        self.write(GPIO_DIR, 0x80) # DIR

        self.write(GPIO_DAT, 0x00) # DAT

        self.write(GPIO_EN, 0x80) # EN

        # Set up the auto-config
        self.write(AUTO_USL, 0xc9) # for 3.3V operation
        self.write(AUTO_TL, 0xb5)  # 90% of USL
        self.write(AUTO_LSL, 0x83) # 65% of USL
        self.write(AUTO_CFG0, 0x0b) # note: AFES == FFI
        self.write(AUTO_CFG1, 0x00)

        # Turn on first 11 electrodes, and run auto-config
        self.write(ECR, 0x0b)

    def reset(self):
        self.write(0x80, 0x63)

    def touches(self):
        try:
            return self.bus.read_word_data(self.addr, 0)
        except IOError:
            return 0x0000

    def spin(self):
        import time
        while 1:
            print '0x%04x' % (self.touches(),)
            time.sleep(0.1)


def run():
    chip = MPR121(WHICH_BUS)
    chip.config()
    ### do something