DEVICE FOR CHECKING NUMBERS AND METHOD FOR CHECKING NUMBERS

Abstract

A device for checking numbers consists of a multiplexer (101) with a controller module (106) linked to it. An output of the multiplexer is connected to a first input of a register (102), which is an element of memory, while a first output of the controller module (106) is connected to an input of a memory (103) and a second input of the register (102). An output of the register (102) and an output of the memory (103) are connected to inputs of the adder (104), which adds on its output a number, stored in the register (102) and a number written in the memory (103) at an address indicated by the controller module (106). The adder (104) generates on its output a carry-out signal, informing about overflow, which is passed to a first controlling input of the controller module (106), which manages operation of the device checking numbers. A second controlling input of the controller module (106) is coupled a logical NOR type gate (105) passing a zero signal informing that the number on the output of the adder (104) equals zero.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/899,514, filed Jul. 26, 2004, and claims priority benefits to Polish Patent Application No. P-361531, filed Aug. 1, 2003, the contents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for checking numbers and a method for checking numbers, which can be applied in a digital television decoder, especially designed for comparing PID numbers (Packet Identifier) of received data packets.

2. Brief Description of the Background of the Invention Including Prior Art

The method of implementing a PID filter (Packet Identifier) was described in the patent application EP 0 949 808. According to this method a table is created. The table stores values used for the purpose of comparison. The system uses a comparator to find out whether the given values—the first from circuit inputs and the second from the table—are equal. Moreover, a FIFO type (First-in, First-out) output queue is also applied. The output FIFO queue allows for initiating read operations, until such a time that the input data packet is defined as the correct one. When the PID data are given onto the system inputs, the comparator compares the given value with the stored values table, which was created earlier by the programming circuit.

In the case of joining or multiplexing of two signal streams, in which certain services have the same PID numbers, packets from the two services may mix. This may, at a later stage of signal processing, cause a conflict of PID numbers.

SUMMARY OF THE INVENTION

Purposes of the Invention

It is an object of this invention to provide a device for multiplexing different signal streams without causing a conflict of PID numbers.

It is another object of this invention to provide a method for increasing security while sending packets from few services.

These and other objects and advantages of the present invention will become apparent from the detailed description, which follows.

BRIEF DESCRIPTION OF THE INVENTION

In order to eliminate conflicts of PID numbers, a circuit was developed, that allows changing the PID numbers of one or more of the processed packets, prior to the further stages of signal processing. For this purpose, the circuit was designed to ensure the possibility of checking if a PID number is located within a specific range, and to allow for modifying its value. According to the invention, data used for comparisons are stored in RAM or ROM memory, while the comparison process itself is conducted by the means of a recurrence system, the structure of which does not include comparators. This system was realized through the appropriate control of the integral adder.

The circuit for checking numbers includes a multiplexer for receiving a checked number linked to a controller module. The multiplexer has a first multiplexer input, a second multiplexer input and a multiplexer output. The controller module linked to the multiplexer has a controller module output, a first controlling input and a second controlling input. The output of the multiplexer is connected to one input of a register, which is a memory element, while one of the outputs of the controller module is connected to a memory, and the second to the second register input. The register is used for temporary storing a temporary number whereas the memory is used for storing information related to ranges of incoming PID numbers. The register output and the memory output are connected to inputs of the adder, which sums up, on its output, the number stored in the register and the number stored in the memory under an address indicated by the controller module and sends a result of summing to the multiplexer. On its output, the adder also generates an informing signal, which is transmitted to one of the control inputs of the controller module, which in turn manages the operation of the whole system. The carry-out signal causes modification of the checked number sent to the first multiplexer input when the checked number is within a checked range belonging to the ranges of incoming PID numbers. A NOR-type logical gate is placed in the second controlling track of the controller. This gate generates a signal, informing that the number, on the output of the adder, is equal to zero and the checked number is equal to a lower-limit value or an upper-limit value of a checked range of the incoming PID numbers.

The method of checking whether a given number is within the given range goes as follows. A reading is taken from the memory of the lower coefficient of the register range. Numbers from the register are summed with the value from memory, given at the input of the adder. If the result, i.e. a first sum, of adding causes the carry-out output to be set, it means that the number is higher than the lower range value.

The result of the previous summing is then recorded in the register, and the upper coefficient of register range is read from the memory. This coefficient is added to the previous result. If the result, i.e. a second sum, of the adding does not cause the carry-out value to be set, it means that the number—in the case when the previous addition set the index of carry-out—is within the checked range. In the case, when the given number is within the checked or defined range, it is changed by the defined value. Both, the lower-limit and the upper-limit coefficients of the range, as well as the coefficient of correction are stored in the memory. The values of numbers is stored according to the sequence of checking under the consecutive addresses in the memory, where the first coefficient is the lower-limit coefficient of the range, the second coefficient is the upper-limit coefficient of the range, and the last coefficient is the correction coefficient. In the case where the number is within the appropriate range, the correction coefficient is read from the memory and added to the previous result of adding. In order to check if a number is equal to the lower-limit or the upper-limit value of the range of the incoming PID numbers, a check is made if the first sum or the second sum equals 0. The number is also corrected by the correction coefficient when the first sum or the second sum equals zero.

The lower and the upper coefficients depend on the lower-limit and the upper-limit values. The lower coefficient equals (−low_range_X), the upper coefficient equals (low_range_X−high_range_X) and the correction coefficient equals (correction_X+high_range_X), where correction_X is a correction value, low_range_X is the lower-limit value of the range of the incoming PID numbers and the high_range_X is the upper-limit value of the range of the incoming PID numbers. The lower-limit and the upper-limit values of each range of the ranges are stored in a sequence and at increasing addresses of the memory wherein a first value of the sequence is the lower coefficient, a second value of the sequence is the upper coefficient and a third value of the sequence is the correction coefficient.

The novel features, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings one of the possible embodiments of the present invention is shown, where:

FIG. 1 is a schematic diagram of a circuit for checking numbers;

FIG. 2 is a memory map;

FIG. 3 is a flow chart of operation of the circuit shown in FIG. 1; and

FIG. 4 is a graph of states of a controller module.

DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENT

As it has been shown in FIG. 1, in which the bold arrows mark multi-bit signals, the digital circuit performing a function of checking numbers contains a multiplexer 101 and a controller module 106 connected to it. An output of the multiplexer is connected to a first input of a register 102, which is a memory element. One of outputs, for example a first output of the controller module 106 is connected to an address input of a memory 103, and the second output is connected to a second input of the register 102. An output of the register 102 and an output of the memory 103 are connected to inputs of an adder 104, which sums—on its output—the number stored in the register 102 and the number recorded in the memory 103 at an address indicated by the controller module 106. The result of adding is called a first sum and a second sum. The adder 104 also generates, on its output, a CARRY_OUT signal 115, informing about the carry-out. This signal is transmitted to one of controlling inputs, for example a first controlling input, of the controller module 106 managing the operation of the entire circuit. In the second controlling track of the controller module 106, a NOR-type logical gate 105 is located. It generates the signal ZERO 114, informing that the number on the output of the adder 104 is equal to zero. This signal is transmitted to the input of the controller module 106. Operation of the controller is initiated by the signal START 111.

The ZERO signal 114 is used to determine whether a number is equal to a lower or an upper limit of a checked range. The NOR gate can be omitted when there is only a need to check if a number is greater than the lower limit and smaller than the upper limit.

On its outputs, the multiplexer 101 may produce either a new number or the number provided by the adder, while the controller module 106 decides, which of the input values are to appear on the outputs of the multiplexer. The input number 112, the current state of the adder, and a signal controlling the choice, generated by the controller module 106, are passed to the inputs of the multiplexer 101. The register 102 is the element, which stores the number read from the output of the multiplexer 101. The moment of latching of the input data is controlled by the controller module 106 that caused that the adder 104 generates an output signal, namely the CARRY_OUT signal 115, which informs about the carry-out. The task of the adder 104, as mentioned above, is to put to the output, the sum of the number stored in the register 102, and the number recorded in the memory 103 at the address, indicated by the controller module 106. The adder 104 does not have a carry-in signal. The number from register 102 and a number recorded in the memory 103, are given to the inputs of the adder 104. Limit coefficients of the range and a correction coefficient, with which the number stored in the register 102 should be modified, are stored in the memory 103. The input signals and the addresses, are controlled by the controller module 106, which manages the operation of the entire circuit by sending control signals to the modules 101, 102, 103.

In the described circuit, the limit coefficients of the range are placed in the memory 103. These coefficients are: a lower L_range_X and an upper U_range_X—used for comparisons, as well as the coefficient Corr_X—with which the number should be modified. The memory may be either RAM or ROM, depending on the requirements of the circuit. In other embodiments, it maybe a circuit of multiplexers, giving specific values (ranges) depending on signals from the controller module. Thanks to the setting of numbers, presented below and placed in RAM memory, one individual carry-out signal from the adder suffices to enable the controller module to determine if the number falls within the range.

The circuit memory map is shown in FIG. 2. Data are recorded in the memory according to the following sequence: the lower coefficient, called also a lower-limit coefficient of the range i.e. L_range_X 201, the upper coefficient, called also an upper-limit coefficient of the range, i.e. U_range_X 202, and lastly the correction coefficient i.e. Corr_X 203. In order for the circuit to function properly, the numbers of the L_range_X, the U_range_X and the Corr_X should be calculated as given below. It is assumed that the value of the high_range_X is the upper-limit value of the range of the incoming PID numbers, the low_range_X is the lower-limit value of the range of the incoming PID numbers, and the correction_X is the correction value.

L_range_X=−low_range_X
U_range_X=−(high_range_X−low_range_X)
Corr_X=correction_X+high_range_X

FIG. 3 shows the method of operation of the circuit shown in FIG. 1. The procedure starts in step 301, where the first range is set. Next, in step 302, a check is performed to find out whether the number is greater or equal to the lower-limit value of the checked range, and—at the same time—whether the number is lower or equal to the upper-limit value of the checked range. If the number is within this range, it is modified in step 303. In the opposite case, in step 305 a check is performed to establish if all ranges were checked. If not, a move to step 306 is made. In the opposite case, the procedure is concluded in step 304. If there was a move made to step 306, the next range to be checked is collected.

The graph of the state of a block comparing the numbers—the controller module 106—is shown in FIG. 4. In an idle state, i.e. in state 401, the circuit waits until the condition A is fulfilled, i.e. until the signal START 111 is received. After receiving it, the circuit sets the signal FOUND 113 to zero, and resets the memory address counter. It then moves on to state 402, where a check of lower range is made. In state 402, the number from the input circuit is written in the register 102. In this state, a reading of the coefficient L_range_X, from the memory 103, is also made, and the number from the register 102 is added to the value given on the input of the adder 104 from the memory 103. If the result of the adding causes the setting of the carry-out signal, it means that the number is greater than value of the lower range. Next, the circuit moves to state 403, where the upper range is checked, increasing the counter of address value of the memory 103 and storing the occurrence of the carry-out.

In state 403, the result of the previous addition is written in the register 102 and the coefficient U_range_X is read from the memory 103. This coefficient is added to the previous result. If the result of the summing does not cause the setting of the carry-out indicator, and if the previous adding has set the carry-out indicator, it means that the number is lower than the upper value of the range. The circuit moves on to state 404, where the number is modified with the set value. In state 404, the carry-out value, stored in state 403 is updated. This variable is set, if the carry-out appeared at the first adding, and did not appear at the second adding. In such case, the number from the input falls within range low_range_X and high_range_X.

In state 404, the coefficient Corr_X is read from the memory 103, and added to the previous result of the adding, which saves one cycle of the timer. This timer cycle could have been used to store the original value in the register, in the case when the previously generated sum had not been used. Thanks to it, if the comparison indicated that the number falls within the range, there is a number modified with correction value correction_x at the output of the adder 104. In the case the given number is found to fall within the checked range (condition B), a shift to state 401 is made, and the found indicator is set. A move to state 401 is also made in the case when all the ranges are found to have been checked (memory address>=max, where max=3*n−1, and n means the number of ranges from FIG. 2). In such a case, the ‘found’ signal 113 is reset. If the number does not fall within the checked range, and if all ranges were not checked (condition C), there is a move made to state 402, with a simultaneous increase of the address counter. The whole process of checking the numbers starts again.

An exemplary process of comparing and correcting the number, placed on the input of the circuit, is presented below. When three-bit numbers: low_range_X, high_range_X, correction_X, and number, are used, it should be noticed that the most significant bit—after changing the numbers to four-bit—is treated either as a sign bit (for example for negative numbers L_range_X and U_range_X), or as a normal informational bit (for numbers greater than 7, result after correction of a number):

low_range_X=0100

L_range_X=1100

high_range_X=0110

L_range_X=1110

correction_X=0011

Corr_X=1001

number=0101

First sum=0001, carry signal is set

Second sum=1111, carry signal is not set

After correction=1000, carry signal is set

The device according to the present invention can be applied in a situation where data packets from two exemplary streams A, B are to be multiplexed into one output stream C. When packets of the stream A have identifiers in the range 100 . . . 199 and the packets of the stream B have identifiers in the range 180 . . . 279 a conflict would arise if the packets were multiplexed without identifiers correction. According to the invention packets of the stream B can be processed by the device where the low_range_B can be set to 180, the high_range_B can be set to 199 and the correction may equal 100. In this case in the output stream C packets with identification numbers 100-199 originate from the stream A and packets unchanged 200-279 originate from the stream B while modified packets 280-299 of the stream C were processed by the filter.

An example of the implementation of the controller module 106, is described below in a code using the VHDL language. The presented example of implementation co-operates with the asynchronous memory, which is controlled only by the address input. In addition, the following timer (CLK), signals are used: the resetting (RESET) signal, and the PID_SECTION signal, which defines the range (filter) in which the number was found. In FIG. 1 the CARRY_OUT signal was marked as 115, the START signal was marked as 111, and the FOUND signal was marked as 113.

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
entity Controller is
port (
CLK: in STD_LOGIC;
RST: in STD_LOGIC;
START: in STD_LOGIC;
CARRY_OUT: in STD_LOGIC;
ZERO: in STD_LOGIC;
SEL1: out STD_LOGIC;
LOAD: out STD_LOGIC;
FOUND: out STD_LOGIC;
ADDR: out STD_LOGIC_VECTOR(5 downto 0);
PID_SECTION: out STD_LOGIC_VECTOR (3 downto 0)
);
end Controller;
architecture Controller_arch of Controller is
type states is (IDLE, CHECK_LOW, CHECK_HIGH, CORRECT);
constant MAX_ADDRESS : STD_LOGIC_VECTOR(5 downto 0) := “101111”;
signal state : states;
signal carry_out_state : STD_LOGIC;
signal address : STD_LOGIC_VECTOR(5 downto 0);
signal pid_sect : STD_LOGIC_VECTOR(3 downto 0);
begin
ADDR <= address;
LOAD <= ‘1’ when (state=CHECK_LOW)
or (state=CHECK_HIGH)
or ((state=CORRECT)
and (carry_out_state=‘0’)) else START;
PID_SECTION <= pid_sect;
machine: process(CLK, RST)
begin
if RST=‘0’ then
state <= IDLE;
FOUND <= ‘0’;
address <= (others=>‘0’);
pid_sect <= (others=>‘0’);
address <= (others=>‘0’);
SEL1 <= ‘0’;
elsif CLK′event and CLK=‘1’ then
case state is
when IDLE => if start=‘1’ then
state <= CHECK_LOW;
FOUND <= ‘0’;
address <= (others=>‘0’);
pid_sect <= (others=>‘0’);
SEL1 <= ‘1’;
end if;
when CHECK_LOW => carry_out_state <= CARRY_OUT or ZERO;
address <= address + 1;
state <= CHECK_HIGH;
SEL1 <= ‘1’;
when CHECK_HIGH => carry_out_state <= carry_out_state
and ((not CARRY_OUT) or ZERO);
address <= address + 1;
state <= CORRECT;
SEL1 <= ‘0’;
when CORRECT => SEL1 <= ‘0’;
if carry_out_state = ‘1’
or address = MAX_ADDRESS then
state <= IDLE;
FOUND <= carry_out_state;
else
pid_sect <= pid_sect + 1;
-- increase filter number
state <= CHECK_LOW;
address <= address + 1;
SEL1 <= ‘1’;
end if;
end case;
end if;
end process machine;
end Controller_arch;

The preferred embodiments having been thus described, it will now be evident to those skilled in the art that further variation thereto may be contemplated. Such variations are not regarded as a departure from the invention, the true scope of the invention being set forth in the claims appended hereto.

Claims

1. A device for checking n-bit numbers comprising

a multiplexer having a first multiplexer input for receiving an input number, a second multiplexer input for receiving a number, a controlling input and a multiplexer output;

a controller module comprising a first controlling input, a first controlling output connected to the controlling input of the multiplexer, a second controlling output and a controller module output;

a register for storing a multiplexer output number output by the multiplexer and having a controlling input connected to the second controlling output of the controller module, a register input connected to the multiplexer output and a register output;

a memory for storing information related to a range of input numbers, the memory having a storage input connected to the controller module output and a storage output; and

an (n+i)-bit adder comprising a first adder input connected to the register output, a second adder input connected to the storage output of the memory, an adder output and a carry-out output wherein the adder adds the number stored in the register and a number stored in the memory at an address indicated by the controller module, and outputs a result of addition via the adder output, to the second multiplexer input and generates at the carry-out output a carry-out signal informing about carry-out and being passed to the first controlling input of the controller module.

2. The device of claim 1, wherein the adder further outputs a zero signal when the result of addition equals 0.

3. The device of claim 2, wherein the controller module comprises a second controlling input for receiving the zero signal.

4. The device of claim 1, wherein the controller module stores the carry value output by the adder.

5. The device of claim 1, wherein the n+i equals n+1.

6. The device of claim 1, wherein the memory stores a correction coefficient.

7. The device of claim 6, wherein the controller module causes modification of the input number by the correction coefficient when the input number is within the range.

8. A method of checking n-bit numbers, the method comprising the steps of:

obtaining a lower limit and an upper limit of a range;

computing an (n+i)-bit lower coefficient as (−(the lower limit));

computing an (n+i)-bit upper coefficient as (−((the upper limit)−(the lower limit)));

calculating by an (n+i)-bit adder a first sum by adding the lower coefficient and an input number;

storing a first carry-out value of the first sum;

calculating a second sum by adding the upper coefficient and the first sum;

storing a second carry-out value of the second sum; and

determining that the input number is within the range when the first carry-out value of the first sum signals overflow and the second carry-out value of the second sum does not signal overflow.

9. The device of claim 1, wherein the n+i equals n+1.

10. The method of claim 8 wherein more than one range is checked against the input number.

11. The method, of claim 8, wherein in order to check if the n-bit input number is equal to the lower limit or the upper limit of the range, it is checked whether the first sum or the second sum equals 0.

12. The method, of claim 8, further comprising the step of changing the n-bit input number by a correction coefficient when the number is within the range.

13. The method, of claim 8, further comprising the steps of changing the n-bit input number by a correction coefficient when the first sum or the second sum equals zero.

14. The method, of claim 8, further comprising the steps of defining a sequential correction coefficient, checking sequentially further ranges of the ranges of input numbers and changing the n-bit input number by the sequential correction coefficient when the number is within the range.

15. The method, of claim 12, wherein the correction coefficient equals ((correction value)+(upper limit)).

16. The method of claim 14, wherein values of each range are stored in a sequence and at increasing addresses of the memory wherein a first value of the sequence is the lower coefficient, a second value of the sequence is the upper coefficient and a third value of the sequence is the correction coefficient.

17. The method of claim 8, wherein n equals 13.