Method to optimize general-purpose input/output interface pad assignments for integrated circuit
The present disclosure relates to an innovative method of assigning signals to general-purpose input/output pads of an integrated circuit chip. An inductance matrix for the input/output pads is obtained. A candidate assignment is made of a differential signal to a pair of the input/output pads, and a differential mutual inductance is determined for each open pad location in relation to the pair of input/output pads. Single-ended signals are assigned to open pad locations having the lowest differential mutual inductances. The jitter contribution due to each assigned single-ended signal is computed, and a total jitter is updated. In a first embodiment, said assigning, computing and updating steps are repeated until the total jitter exceeds a total jitter budget. In a second embodiment, said assigning, computing and updating steps are repeated until a number of assigned single-ended signals is equal to a target number. Other embodiments and features are also disclosed.
1. A method of assigning signals to general-purpose input/output pads of an integrated circuit chip, the method comprising:
obtaining, using a computer, an inductance matrix for the input/output pads;
making a candidate assignment of a differential signal to a pair of the input/output pads;
determining a differential mutual inductance for each open pad location in relation to the pair of input/output pads;
assigning a single-ended signal to an open pad location having a lowest differential mutual inductance;
computing a jitter contribution due to the single-ended signal; and
updating a total jitter with the jitter contribution.
2. The method of claim 1 , further comprising:
repeating said assigning, computing and updating steps until the total jitter exceeds a total jitter budget.
3. The method of claim 2 , further comprising:
when the total jitter exceeds the total jitter budget, undoing a preceding assignment and reducing the total jitter by the jitter contribution of the preceding assignment; and
storing a resultant set of signal-to-pad assignments for the single-ended signals, along with the total jitter, in relation to the candidate assignment of the differential signal.
4. The method of claim 3 , further comprising:
when there is a further candidate assignment to process, looping back and making the further candidate assignment, then repeating said determining, assigning, computing, updating and repeating steps.
5. The method of claim 4 , further comprising:
selecting and outputting an optimal assignment that is the candidate assignment with a highest number of single-ended signals being assigned within the total jitter budget.
6. The method of claim 1 , further comprising:
repeating said assigning, computing and updating steps until a number of assigned single-ended signals is equal to a target number.
7. The method of claim 6 , further comprising:
when the number of assigned single-ended signals is equal to the target number, storing a resultant set of signal-to-pad assignments for the single-ended signals, along with the total jitter, in relation to the candidate assignment of the differential signal.
8. The method of claim 7 , further comprising:
when there is a further candidate assignment to process, looping back and making the further candidate assignment, then repeating said determining, assigning, computing, updating and repeating steps.
9. The method of claim 8 , further comprising:
selecting and outputting an optimal assignment that is the candidate assignment with a highest number of single-ended signals being assigned within the total jitter budget.
10. The method of claim 1 , wherein the candidate assignment involves assigning a plurality of differential signals to a plurality of pairs of the input/output pads.
11. The method of claim 1 , further comprising:
pre-assigning power-related inputs to the input/output pads.
12. The method of claim 1 , further comprising:
sorting the open pad locations by their differential mutual inductance.
13. A non-transitory computer-readable medium comprising instructions stored thereon, that when executed on a processor, perform the steps of:
obtaining, using a computer, an inductance matrix for the input/output pads of an integrated circuit chip;
making a candidate assignment of a differential signal to a pair of the input/output pads;
determining a differential mutual inductance for each open pad location in relation to the pair of input/output pads;
assigning a single-ended signal to an open pad location having a lowest differential mutual inductance;
computing a jitter contribution due to the single-ended signal; and
updating a total jitter with the jitter contribution.
14. The non-transitory computer-readable medium of claim 13 , wherein the steps further comprise:
repeating said assigning, computing and updating steps until the total jitter exceeds a total jitter budget.
15. The non-transitory computer-readable medium of claim 14 , wherein the steps further comprise:
when the total jitter exceeds the total jitter budget, undoing a preceding assignment and reducing the total jitter by the jitter contribution of the preceding assignment; and
storing a resultant set of signal-to-pad assignments for the single-ended signals, along with the total jitter, in relation to the candidate assignment of the differential signal.
16. The non-transitory computer-readable medium of claim 15 , wherein the steps further comprise:
when there is a further candidate assignment to process, looping back and making the further candidate assignment, then repeating said determining, assigning, computing, updating and repeating steps.
17. The non-transitory computer-readable medium of claim 16 , wherein the steps further comprise:
selecting and outputting an optimal assignment that is the candidate assignment with a highest number of single-ended signals being assigned within the total jitter budget.
18. The non-transitory computer-readable medium of claim 13 , wherein the steps further comprise:
repeating said assigning, computing and updating steps until a number of assigned single-ended signals is equal to a target number.
19. The non-transitory computer-readable medium of claim 18 , wherein the steps further comprise:
when the number of assigned single-ended signals is equal to the target number, storing a resultant set of signal-to-pad assignments for the single-ended signals, along with the total jitter, in relation to the candidate assignment of the differential signal.
20. The non-transitory computer-readable medium of claim 19 , wherein the steps further comprise:
when there is a further candidate assignment to process, looping back and making the further candidate assignment, then repeating said determining, assigning, computing, updating and repeating steps; and
selecting and outputting an optimal assignment that is the candidate assignment with a highest number of single-ended signals being assigned within the total jitter budget.
21. A system for assigning signals to general-purpose input/output pads of an integrated circuit chip, the system comprising:
an electronic-design automation tool executing on a computer; and
a signal-to-pad assignment module of the electronic-design automation tool, wherein the module is programmed to perform the steps of
obtaining, using the computer, an inductance matrix for the input/output pads,
making a candidate assignment of a differential signal to a pair of the input/output pads,
determining a differential mutual inductance for each open pad location in relation to the pair of input/output pads,
assigning a single-ended signal to an open pad location having a lowest differential mutual inductance,
computing a jitter contribution due to the single-ended signal, and
updating a total jitter with the jitter contribution.