Memory organization and output sequencer for a signal processor

• US 4,908,825 A
• Filed: 04/08/1988
• Issued: 03/13/1990
• Est. Priority Date: 04/08/1988
• Status: Expired due to Term

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Vea, Matthew J. J.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Chin, Wellington
• Application Number:
  US07/179,269
• Time in Patent Office: 704 Days
• Field of Search: 370/110.3, 379/283
• US Class Current: 370/526
• CPC Class Codes: H04Q 1/4575 which are transmitted in digital form

Abstract

A specialized tone receiver is capable of detecting tones on many different digital signal channels simultaneously. A single memory is used to buffer incoming digital signals. Independent write and read sequencers write samples into and read samples from the buffer memory, respectively. The write sequencer writes all samples corresponding to a given sample time at essentially the same time, while the read sequencer reads out all of the samples corresponding to a given channel of interest in reverse sequential chronological order (i.e., in the opposite order from the order the samples were written) beginning with the most current sample. A priority structure controls access to the buffer memory, with the read sequencer being granted a higher access priority than the write sequencer. A filtering algorithm symmetrical in time and executed by a digital signal processor controlled by the same microcode sequencer which controls the read sequencer is used to detect specific frequencies present in the read channel samples. A separate, slower processor performs time validation functions on a time scale which is extremely slow compared with the time scale at which frequency validation is performed. The specialized tone receiver is extremely fast, requires only a single, relatively small input buffer memory (e.g., 128K bytes for a 512 channel PCM bus), and is capable of detecting several different specialized signalling tones on all of the channels of a multiport mulitchannel PCM bus in very close to real time.

Claims

1. A specialized tone receiver of the type which is connected to a digital signal bus carrying a pulse code modulated digital signal sample stream corresponding to a speech channel, said receiver comprising:

input buffer memory means for temporarily storing said bus digital signal sample stream;

write sequencer means connected to said memory means and also connected to receive said signal sample stream for writing said sample stream into said input buffer memory means in a first sequential chronological order;

read sequencer means connected to said memory means for reading said written sample stream from said memory means in a second sequential chronological order opposite said first chronological order; and

digital signal processing means connected to receive said read sample stream for detecting at least one prespecified frequency component within said sample stream.

2. A receiver as in claim 1 wherein said read sequencer means reads said sample stream from said memory means in reverse chronological order beginning with a sample in said stream corresponding to a sample time T-1 substantially while said write sequencer means continues to write said sample stream into said input buffer memory in chronological order beginning with a sample in said stream corresponding to a sample time T.

3. A receiver as in claim 1 further including memory arbiter means connected to said read sequencer means, said write sequencer means, and said memory means, for alternately granting access to said memory means by said read sequencer means and said write sequencer means in accordance with a predetermined priority structure, said priority structure awarding said read sequencer means a higher priority than said write sequencer means.

4. A receiver as in claim 1 wherein said digital signal processor means includes means for filtering said read sample stream using a filtering algorithm which is symmetrical with time.

5. A specialized tone receiving apparatus of the type which is connected to a time division multiplexed digital signal bus carrying time division multiplexed pulse code modulated plural digital signal sample sequences corresponding to associated plural independent speech channels, said apparatus comprising:

input buffer memory means for temporarily storing said bus digital signal sample sequences;

write sequencer means connected to said memory means and also connected to said digital signal bus for writing said plural digital signal sample sequences into said input buffer memory means, the sequence of samples corresponding to each of said plural independent speech channels being written into said memory means in a first sequential chronological order;

read sequencer means connected to said memory means for selecting one of said plural independent speech channels and for reading the signal sample sequence corresponding to said selected speech channel from said memory means in a second sequential chronological order opposite said first chronological order; and

digital signal processing means connected to receive said read signal sample sequence for detecting at least one prespecified frequency component within said read signal sample sequence.

6. Apparatus as in claim 5 wherein:

said write sequencer means includes a first channel counter means for maintaining a first channel count, a first sample counter means for maintaining a first sample count, and means for addressing said memory means in accordance with said first channel and sample count;

said write sequencer means includes a second channel counter means for maintaining a second channel count, a second sample counter means for maintaining a second sample count, and means for addressing said memory means in accordance with said second channel and sample count; and

said apparatus further includes means for loading the contents of said first sample counter means into said second channel counter means.

7. Apparatus as in claim 5 wherein:

said write sequencer means includes a first channel counter means for maintaining a first channel count, a first sample counter means for maintaining a first sample count, and means for addressing said memory means in accordance with said first channel and sample count;

said write sequencer means includes a second channel counter means for maintaining a second channel count, a second sample counter means for maintaining a second sample count, and means for addressing said memory means in accordance with said second channel and sample count; and

said apparatus further includes means for periodically incrementing the contents of said first sample counter means and means for periodically decrementing the contents of said second sample counter means.

8. Apparatus in claim 7 wherein:

said first-mentioned incrementing means increments the contents of said first sample counter means at a first rate;

said decrementing means decrements said second sample counter means at a second rate; and

said method further includes;

means for incrementing the contents of said first channel counter means periodically at a rate which exceeds the first rate, and

means for incrementing the contents of said second channel counter means periodically at a rate which is less than the second rate.

9. A specialized tone receiver of the type which is connected to a digital signal bus carrying a pulse code modulated digital signal sample stream corresponding to a speech channel, said receiver comprising:

input buffer memory means for temporarily storing said digital signal sample stream;

write sequencer means connected to said memory means and also connected to receive said digital sample stream for writing said digital signal sample stream into said input buffer memory means in a sequential chronological order;

read sequencer means connected to said memory means for reading said written digital signal sample stream from said memory means more than once; and

digital signal processing means connected to receive said read digital signal sample streams for detecting a first prespecified frequency component within said read digital signal sample stream the first time said read sequencer means reads said digital signal sample stream and for detecting a second prespecified frequency component within said read digital signal sample stream a subsequent time said read sequencer means reads said digital signal sample stream.

10. A receiver as in claim 9 wherein:

said write sequencer means writes said digital signal sample stream in a first chronological order; and

said read sequencer means reads said stored digital signal sample stream in a second chronological order opposite said first chronological order beginning with the last sample in said stream written by said read sequencer means.

11. A method of receiving and detecting specialized tones on a digital signal bus carrying a pulse code modulated digital signal sample stream corresponding to a speech channel, said method comprising the steps of:

temporarily storing said bus digital signal sample stream in an input buffer memory;

writing said sample stream into said input buffer memory in a first sequential chronological order;

reading said written sample stream from said input buffer memory in a second sequential chronological order opposite said first chronological order; and

detecting at least one prespecified frequency component within said read sample stream.

12. A method as in claim 11 further including the step of alternately granting access of said input buffer memory to said reading step and to said writing step in accordance with a predetermined priority wherein said reading step has a higher priority than said writing step.

13. A method as in claim 11 wherein said detecting means includes the step of filtering said read sample stream symmetrically with time.

14. A specialized tone receiving method for receiving and detecting specialized tones simultaneously in plural independent time division multiplexed PCM speech channels each carrying a corresponding digital sample sequence, said method comprising the steps of:

temporarily storing said digital sample sequences carried by said plural speech channels in an input buffer memory.

writing said digital sample sequences into said memory, including the step of writing each of said sample sequences in a first sequential chronological order;

selecting one of said speech channels;

reading the signal sample sequence corresponding to said selected speech channel from said input buffer memory in a second sequential chronological order opposite said first chronological order; and

detecting at least one prespecified frequency component within said read signal sample sequence.

15. A method as in claim 14 wherein:

said method further includes repeating said reading step at least once to provide first and second identical read signal sample sequences; and

said detecting step includes the following steps;

detecting a first frequency component in said first read signal sample sequence, and

detecting a second frequency component different from said first frequency component in said second read signal sample sequence.

16. A method as in claim 14 wherein said detecting step comprises the step of symmetrically filtering said read signal sample sequence.

17. A method as in claim 14 further including the step of alternately granting access of said input buffer memory to said reading step and to said writing step in accordance with a predetermined priority wherein said reading step has a higher priority than said writing step.

18. A method as in claim 14 wherein said selecting, reading and detecting steps are performed for each of said digital sample sequences, and said writing step is continually performed.

19. A method for detecting specialized tones in a pulse code modulated digital signal sample stream corresponding to a speech channel, said method including the following steps:

(a) continually writing portions of said digital signal sample stream into a memory;

(b) temporarily storing the written portions of said digital signal sample stream in said memory;

(c) reading a written digital signal sample stream portion from said memory;

(d) detecting a first prespecified frequency component within said read sample stream portion read by said reading step (c);

(e) again reading said written digital signal sample stream portion from said memory; and

(f) detecting a second prespecified frequency component different from said first component within said read sample stream portion read by said again reading step (e).

20. A method as in claim 19 wherein said writing step (a) writes said sample stream portion in a first order, and said reading and again reading steps (c) and (e) each read said temporarily stored sample stream portion in a second order opposite said first order.

21. A method as in claim 19 further including the step of alternately granting access of said input buffer memory to:

(i) said reading step (c) and again reading step (e), and (ii) to said writing step (a) in accordance with a predetermined priority wherein said reading steps (c), (e) have a higher priority than said writing step (a).