#!/usr/bin/env python2 # dtd_parser.py - DTD structure parser # # SPDX-License-Identifier: GPL-2.0-only ''' DTD string parser/generator. Detailed timing descriptor (DTD) is an 18 byte array describing video mode (screen resolution, display properties, etc.) in EDID and used by Intel Option ROM. Option ROM can support multiple video modes, specific mode is picked by the BIOS through the appropriate Option ROM callback function. This program allows to interpret the 18 byte hex DTD dump, and/or modify certain values and generate a new DTD. ''' import sys # # The DTD array format description can be found in # http://en.wikipedia.org/wiki/Extended_display_identification_data, (see the # EDID Detailed Timing Descriptor section). # # The below dictionary describes how different DTD parameters are laid out in # the array. Note that many parameters span multiple bit fields in the DTD. # # The keys in the dictionary are stings (field names), the values are tuples # of either numbers or tri-tuples. If the element of the tuple is a number, it # is the offset in DTD, and the entire byte is used in this field. If the # element is a tri-tuple, its components are (DTD offset, bit shift, field # width). # # The partial values are extracted from the DTD fields and concatenated # together to form actual parameter value. # dtd_descriptor = { 'dclck' : (1, 0), 'hor_active' : ((4, 4, 4), 2), 'hor_blank' : ((4, 0, 4), 3), 'vert_act' : ((7, 4, 4), 5), 'vert_blank' : ((7, 0, 4), 6), 'hsync_offset' : ((11, 6, 2), 8), 'hsync_pulse_width' : ((11, 4, 2), 9), 'vsync_offset' : ((11, 2, 2), (10, 4, 4)), 'vsync_pulse_width' : ((11, 0, 2), (10, 0, 4)), 'hor_image_size' : ((14, 4, 4), 12), 'vert_image_size' : ((14, 0, 4), 13), 'hor_border' : (15,), 'vert_border' : (16,), 'interlaced' : ((17, 7, 1),), 'reserved' : ((17, 5, 2), (17, 0, 1)), 'digital_separate' : ((17, 3, 2),), 'vert_polarity' : ((17, 2, 1),), 'hor_polarity' : ((17, 1, 1),), } PREFIX = 'attr_' class DTD(object): '''An object containing all DTD information. The attributes are created dynamically when the input DTD string is parsed. For each element of the above dictionary two attributes are added: 'attr_<param>' to hold the actual parameter value 'max_attr_<param>' to hold the maximum allowed value for this parameter. ''' def __init__(self): for name in dtd_descriptor: setattr(self, PREFIX + name, 0) def init(self, sarray): '''Initialize the object with values from a DTD array. Inputs: sarray: a string, an array of ASCII hex representations of the 18 DTD bytes. Raises: implicitly raises ValueError or IndexError exceptions in case the input string has less than 18 elements, or some of the elements can not be converted to integer. ''' harray = [int(x, 16) for x in sarray] for name, desc in dtd_descriptor.iteritems(): attr_value = 0 total_width = 0 for tup in desc: if isinstance(tup, tuple): offset, shift, width = tup else: offset, shift, width = tup, 0, 8 mask = (1 << width) - 1 attr_value = (attr_value << width) + ( (harray[offset] >> shift) & mask) total_width += width setattr(self, PREFIX + name, attr_value) setattr(self, 'max_' + PREFIX + name, (1 << total_width) - 1) def __str__(self): text = [] for name in sorted(dtd_descriptor.keys()): text.append('%20s: %d' % (name, getattr(self, PREFIX + name))) return '\n'.join(text) def inhex(self): '''Generate contents of the DTD as a 18 byte ASCII hex array.''' result = [0] * 18 for name, desc in dtd_descriptor.iteritems(): attr_value = getattr(self, PREFIX + name) rdesc = list(desc) rdesc.reverse() for tup in rdesc: if isinstance(tup, tuple): offset, shift, width = tup else: offset, shift, width = tup, 0, 8 mask = (1 << width) - 1 value = attr_value & mask attr_value = attr_value >> width result[offset] = (result[offset] & ~( mask << shift)) | (value << shift) return ' '.join('%2.2x' % x for x in result) def handle_input(self, name): '''Get user input and set a new parameter value if required. Display the parameter name, its current value, and prompt user for a new value. If the user enters a dot, stop processing (return True). Empty user input means that this parameter does not have to change, but the next parameter should be prompted. If input is non-empty, it is interpreted as a hex number, checked if it fits the parameter and the new parameter value is set if checks pass. Inputs: name - a string, parameter name, a key in dtd_descriptor Returns: Boolean, True meaning no more field are required to be modified, False meaning that more field mods need to be prompted.. ''' param = PREFIX + name vmax = getattr(self, 'max_' + param) new_value = raw_input('%s : %d ' % (name, getattr(self, param))) if new_value == '': return False if new_value == '.': return True new_int = int(new_value) if new_int > vmax: print '%s exceeds maximum for %s (%d)' % (new_value, name, vmax) else: setattr(self, param, new_int) return False def main(args): if args[0] == '-m': modify = True base = 1 else: modify = False base = 0 d = DTD() d.init(args[base:]) if modify: for line in str(d).splitlines(): if d.handle_input(line.split(':')[0].strip()): break print d if modify: print d.inhex() if __name__ == '__main__': try: main(sys.argv[1:]) except (ValueError, IndexError): print """ A string of 18 byte values in hex is required. '-m' preceding the string will allow setting new parameter values. """ sys.exit(1)