.. index::
   pair: UniServ; MT protocol
   single: Table download protocol

===================================================
Table download protocol specification (MT protocol)
===================================================

Special constants
-----------------

Here are the protocol constants::

  ESC         0x80000000
  LIT         0x80000001
  C_MASK      0x10000000
  C_START     0x20000000
  C_CKLOW     0x30000000
  C_CKHIGH    0x40000000
  C_DATMASK   0x0FFFFFFF
  C_CMDMASK   0xF0000000

Special functions
-----------------

There are the definitions of some special functions::

  C_MASK(n)   0x10000000 + n
  C_CKLOW(n)  0x30000000 + n
  C_CKHIGH(n) 0x40000000 + n
  C_START(n)  0x20000000 + n

The table of values
-------------------

Table to transmit:
X[i] Y[i], i=0..l

checksum= Sum(i=0..l,X[i]+Y[i])

Sender
------

Start transmission (everything with a delay of "T"),
all integers are transmitted as little endian integers

axle mask: MASK
array length: l

This is the sender pseudo code::

  send ESC
  send ESC
  send C_MASK(MASK)
  send C_CKHIGH(checksum >> 16)
  send C_CKLOW(checksum & 0xFFFF)
  send C_START(l)
  last= ESC
  for i in 0..l
      for val in X[i],Y[i]
          if val==ESC or val==LIT or val==last
              send LIT
          send val
          last= val
  send ESC
  send ESC
   
Receiver
--------

This is the receiver pseudo code::

  mode= MODE_COMMAND
  is_selected= False
  table_checksum= 0
  table_status= STATUS_OK
  checksum= 0
  current_checksum= 0
  status= STATUS_OK
  length= 0
  current_length= 0
  transfer_y= True
  
  loop    
      val= read() // it is ensured that the read value is different each time
      if mode==MODE_VALUE or mode==MODE_LITERAL
          new_data= true
          if mode==MODE_LITERAL
              mode= MODE_VALUE
          else
              if val==ESC
                  mode= MODE_COMMAND
                  new_data= false
                  if is_selected
                      status= STATUS_OK
                      if current_checksum != checksum
                          status= STATUS_CHECKSUM_ERROR
                      if current_length != length
                          status= STATUS_LENGTH_ERROR
                      if status != STATUS_OK
                          <make table X[i],Y[i], l empty>
                      else
                          TABLE_LENGTH= current_length
                      table_status= status
              elsif val==LIT
                  mode= MODE_LITERAL
                  new_data= false
          if is_selected and new_data
              if not transfer_y
                  X[current_length]= val
                  transfer_y= true
              else
                  Y[current_length]= val
                  transfer_y= false
                  current_length= current_length + 1 
              current_checksum = current_checksum + val
      elsif mode==MODE_COMMAND
          code= val & C_CMDMASK
          if code==C_MASK
              if val & (1<<(my_axle_index-1))
                  is_selected= true
              else
                  is_selected= false
          elsif code==C_CKHIGH
              if is_selected
                  checksum= (val & C_DATMASK)<<16
          elsif code==C_CKLOW:
              if is_selected
                  checksum= checksum | (val & C_DATMASK)
          elsif code==C_START
              if is_selected
                  length= val & C_DATMASK
                  current_length= 0
                  transfer_y= false
                  current_checksum= 0
                  status= STATUS_TRANSMITTING
                  mode= MODE_VALUE