Method of link word synchronization
A method for word synchronization can be applied to asynchronous devices including SERDES devices connected across serial lines. A state transition methodology characterizes the state of the device based on control characters received consistently across the serial lines and channels the system to a state of word synchronization. Loss of synchronization and transmission errors lead to a re-establishment of synchronization.
1. A system for synchronously transmitting in one direction digital words of a specific bit-length, comprising:
a first digital device;
a second digital device;
a set of parallel conductors connecting the first digital device and the second digital device;
a plurality of serializers in the first digital device, one coupled to each parallel conductor;
a plurality of deserializers in the second digital device, one coupled to each parallel conductor;
first software or firmware implemented at the first digital device; and
second software or firmware implemented at the second digital device;
wherein, prior to transmitting digital words of the specific bit length, the first software or firmware transmits to the second digital device an enabling idle sequence, including a first control word, simultaneously on each parallel conductor, enabling the second digital device to synchronously receive and deserialize words at the second digital device, and upon synchronization, the first software or firmware serially divides digital words to be transmitted to the second digital device into equal length portions, and transmits each portion separately but simultaneously on a dedicated one of the parallel conductors, the equal length portions received and deserialized back into the original digital word by the deserializers at the second digital device.
2. The system of claim 1 further comprising deserializers at the first digital device and serializers at the second digital device, each coupled to individual ones of the parallel conductors, and wherein, after synchronization at the second digital device for transmissions from the first digital device, the second digital device transmits to the first digital device an enabling idle sequence, including a second control word, simultaneously on each parallel conductor, enabling the first digital device to synchronously receive and deserialize words from the second digital device, completing a synchronization sequence, and upon synchronization at both the first and the second digital device, digital words of the specific bit length are divided and transmitted synchronously in both directions.
3. The system of claim 2 wherein digital words transmitted comprise data packets, and the software or firmware at each digital device, recognizing beginning and end of packets, transmit at least one control word on each parallel conductor simultaneously.
4. The system of claim 3 wherein the software or firmware at each digital device, recognizing an inconsistency of control words sent between packets, suspends transmission of packet data and repeats the synchronization sequence.
5. A method for synchronously transmitting in one direction digital words of a specific bit-length, comprising the steps of:
(a) prior to transmitting digital words of the specific bit length, transmitting by a first software or firmware at a first digital device to a second digital device an enabling idle sequence, including a first control word, simultaneously on each of a plurality of parallel conductors between the two digital devices, enabling software or firmware at the second digital device to synchronously receive and deserialize words at the second digital device; and
(b) upon synchronization, serially dividing, at the first digital device digital words to be transmitted to the second digital device into equal length portions, and transmitting each portion separately but simultaneously on a dedicated one of the parallel conductors, the equal length portions received and deserialized back into the original digital word by deserializers coupled to the parallel conductors at the second digital device.
6. The method of claim 5 further comprising a step for transmitting, after synchronizing from the first digital device to the second digital device, an enabling idle sequence including a second control word control word from the second digital device to the first digital device simultaneously on each of the plurality of parallel conductors between the two digital devices, enabling software or firmware at the first digital device to synchronously receive and deserialize words at the first digital device, whereupon words may be transmitted synchronously in both directions.
7. The method of claim 6 wherein digital words transmitted comprise data packets, and the software or firmware at each digital device, recognizing beginning and end of packets, transmit at least one control word on each parallel conductor simultaneously.
8. The method of claim 7 wherein the software or firmware at each digital device, recognizing an inconsistency of control words sent between packets, suspends transmission of packet data and repeats the synchronization sequence.