#!/usr/bin/python
#Script to read/write the nvram

import sys
import os
import getopt
import struct

nvram_resource='/dev/nvram'

def usage():
    ''' This is the Usage Method '''

    print 'Utility for NVRAM read/write'
    print '\t\t nvram_rd_wr.py --get --offset <offset>'
    print '\t\t nvram_rd_wr.py --set --val <val>  --offset <offset>'
    sys.exit(1)

def nvram_reg_read(nvram_resource,offset):
    fd=os.open(nvram_resource, os.O_RDONLY)
    if(fd<0):
        print 'file open failed %s"%nvram_resource'
        return
    if(os.lseek(fd, offset, os.SEEK_SET) != offset):
        print 'lseek failed on %s'%nvram_resource
        return
    buf=os.read(fd,1)
    reg_val1=ord(buf)
    print 'value %x'%reg_val1
    os.close(fd)

def nvram_reg_write(nvram_resource,offset,val):
    fd=os.open(nvram_resource,os.O_RDWR)
    if(fd<0):
        print 'file open failed %s"%nvram_resource'
        return
    if(os.lseek(fd, offset, os.SEEK_SET) != offset):
        print 'lseek failed on %s'%nvram_resource
        return
    ret=os.write(fd,struct.pack('B',val))
    if(ret != 1):
        print 'write failed %d'%ret
        return
    os.close(fd)

def main(argv):

    ''' The main function will read the user input from the
    command line argument and  process the request  '''

    opts = ''
    val = ''
    choice = ''
    resouce = ''
    offset = ''

    try:
        opts, args = getopt.getopt(argv, "hgs:" , \
        ["val=","offset=","help", "get", "set"])

    except getopt.GetoptError:
        usage()

    if not os.path.exists(nvram_resource):
        print 'NVRAM is not initialized'
        sys.exit(1)

    for opt,arg in opts:

        if opt in ('-h','--help'):
            choice = 'help'

        elif opt in ('-g', '--get'):
            choice = 'get'

        elif opt in ('-s', '--set'):
            choice = 'set'

        elif opt ==  '--offset':
            offset = int(arg,16) - 0xE

        elif opt ==  '--val':
            val = int(arg,16)

    if choice == 'get' and offset != '':
        nvram_reg_read(nvram_resource,offset)

    elif choice == 'set' and offset != '' and val != '':
        nvram_reg_write(nvram_resource,offset,val)

    else:
        usage()

#Calling the main method
if __name__ == "__main__":
    main(sys.argv[1:])