-- routines for ccs811, please load ccs811_setup.lua first

    
    
-- user defined function: read 1 byte of data from device
function read_reg(id, dev_addr, reg_addr, len)
    i2c.start(id)
    i2c.address(id, dev_addr, i2c.TRANSMITTER)
    i2c.write(id, reg_addr)
    i2c.stop(id)
    i2c.start(id)
    i2c.address(id, dev_addr, i2c.RECEIVER)
    c = i2c.read(id, len)
    i2c.stop(id)
    return c
end

-- user defined function: write some data to device
-- with address dev_addr starting from reg_addr
function write_reg(id, dev_addr, reg_addr, data)
    i2c.start(id)
    i2c.address(id, dev_addr, i2c.TRANSMITTER)
    i2c.write(id, reg_addr)
    c = i2c.write(id, data)
    i2c.stop(id)
    return c
end

function ccs811_readStatus()
	local reg = read_reg(0,ADDR_CCS811, CCS811_STATUS,1)
	-- print("Status: "..string.byte(reg))
	return reg
end

function ccs811_readHW()
	reg=read_reg(0,ADDR_CCS811, CCS811_HW_ID,1)
	print("HW-ID: "..string.byte(reg))
	reg=read_reg(0,ADDR_CCS811, CCS811_HW_VERSION,1)
	print("HW-Version: "..string.byte(reg))
end

function ccs811_reset()
	
	-- resets the device
	local ret = write_reg(0, ADDR_CCS811, CCS811_SW_RESET, {0x11, 0xE5, 0x72, 0x8A})
	print("reset bytes written: ".. ret)
	
	tmr.delay(CCS811_WAIT_AFTER_RESET_US)
	
	-- and put it into app mode
	local ret = write_reg(0, ADDR_CCS811, CCS811_APP_START, {})
	tmr.delay(CCS811_WAIT_AFTER_APPSTART_US)
	
	-- Check if the switch was successful
    local status = read_reg(0, ADDR_CCS811, CCS811_STATUS, 1);
      
    if( string.byte(status)~=0x90 ) then
      print("ccs811: Not in app mode, or no valid app: "..string.byte(status))
    end
	
	-- and set measure mode (DRIVE_MODE) to 001 -> measurement every second
	ret=write_reg(0, ADDR_CCS811, CCS811_MEAS_MODE, 0x10)
	print("reset measure mode bytes written: ".. ret)
	
end

function css811_readAppVersion()
	local reg = read_reg(0,ADDR_CCS811, CCS811_FW_APP_VERSION,2)
	print("AppVersion: "..string.byte(reg,1).."."..string.byte(reg,2))
end

function css811_readENV_DATA()
	local reg = read_reg(0,ADDR_CCS811, CCS811_ENV_DATA,4)
	return reg
end
function css811_writeEnvData(hum, temp)


	local reg=css811_readENV_DATA()
	print("ENV_DATA before: hum="..string.byte(reg,1).." "..string.byte(reg,2).."   temp="..string.byte(reg,3).." "..string.byte(reg,4))

	-- see datasheet for calculations
	local phum=math.floor(hum*2) -- we only use the integer part
	local ptemp=math.floor(temp+25)
	local data={phum, 0, ptemp, 0}
	
	local ret = write_reg(0, ADDR_CCS811, CCS811_ENV_DATA, data)
	print(" bytes written "..ret)
	print ("write to ENV_DATA: hum="..phum.."  temp="..ptemp)
	
	local ret=css811_readENV_DATA()
	print("ENV_DATA  after: hum="..string.byte(ret,1).." "..string.byte(ret,2).."   temp="..string.byte(ret,3).." "..string.byte(ret,4))
	
end

function css811_readData()
	
	-- local ret = ccs811_readStatus()
	-- print("Status before read: "..string.byte(ret))
	
	local erg = read_reg(0, ADDR_CCS811, CCS811_ALG_RESULT_DATA, 8) -- we only need the 4 MSB bytes from the proxy register
	
	_CO2 =string.byte(erg,1)*256+string.byte(erg,2)
	_TVOC=string.byte(erg,3)*256+string.byte(erg,4)
	
	print("ccs811 CO2 :".._CO2)
	print("ccs811 TVOC:".._TVOC)	
	
	tmr.delay(1000) -- 1ms delay for new conversion
	
	return erg
end

ccs811_reset()
ccs811_readHW()
css811_readAppVersion()