Goal:
To measure the current consumption of TST and TEQ.
| TEQ: | test for equivalence |
| TST: | test and set |
Theory:
TST and TEQ are simple "and" / "or" logic inside ALU. Thus we expect their current consumption is about the same as the other arithematic operations.
Results:
We tested the case where the value on the bus is switching or not for both TST and TEQ.
| Instruction | Description | Current (mA) | File |
| TST | no bus switch | 117.0 | tst_noswitch.s |
| TEQ | no bus switch | 117.0 | teq_noswitch.s |
| TST | bus switch | 132.3 | tst_switch.s |
| TEQ | bus switch | 125.5 | teq_switch.s |
Conclusion:
Although the current consumption of these instructions is similar to other arithematic operations, it is actually higher. Since the logics involved in performing TST and TEQ seems to be small, we do not understand why they consume more current. A 32-bit addition will go through an adder which is definitely more current hungry than simple logical ANDs. What other logic is involved when doing TST and TEQ?