The ISR also ran an actual-time clock, not for time of day, however for timing button de-bouncing, button-hold time (it had a unique operate for those who hold it for a second or extra), squelch-activation instances, and other things. For an instance of a job that watches for a time on the clock, consider a process whose job it’s to put a battery icon within the decrease-right corner of a 2×16 clever character LCD, with the battery state being proven by how full the icon is, and when the battery gets under a sure level, make the icon blink with a one-second cycle, regardless of other duties running. Having the one real-time clock works out fine if you’re employed it like a room full of people all watching the same clock on the wall to time their particular person tasks. Parts of it initially drove me nuts, but steadily I discovered a strategy to make it all work and make it clear. TM for example: Although eight bits may be sufficient to make the blink fee seem steady, a cyclic-govt multitasking application of this sort will most likely have you ever using 16-bit routines for doing transfers and calculations of instances for different routines, even when the RTC uses more.
All tasks should watch the identical real-time clock counter bytes, and add the specified offsets to get the goal occasions to look ahead to, and keep these target occasions in their variables. Wikipedia has a very brief article on cyclic govt, but on the time of this writing, the instance given there solely exhibits two real duties in the main loop, one to learn a temperature and one to replace the LCD, but then there’s a do-nothing wait to delay so this is barely accomplished ten instances a second! How many different duties there are within the loop is none of any given job’s enterprise. The tasks I had have been all dependent to some extent on time, or on other things having completed (like a byte being shifted in or out on a slowish hardware serial interface), or on a flag being set to indicate whether or not the duty was energetic on the time, or something like that; so each one would possibly: 1. Check to see if it is even presupposed to be energetic in the mean time. SET ; See if a byte got here in. FLAG is set however no routine makes use of it before ; another key comes along, the primary one is overwritten and lost.
KEY TOGGLE ; toggle the shift key flag. Was it the shift key? For the reason that shift key can not repeat, any key release from state 2 turns off the shift. KEY ; See if it was the shift key. KEY under which selects a row to pull up. Repeating keys go on to state 2 with a repeat time, however non-repeating ones come here, and state three simply waits till the ; key is up after which resets the state to 0. If it was the shift key, you leave the shift standing alone; but if it was a ; different key, then shift has completed its job so state three clears the shift standing before going back to state 0. ; ; Four-byte variable TIMER gets incremented by the ISR, from interrupts from a Via T1 (or similar hardware timer). 13, regardless of whether or not shift was pressed or not. We get right here from state 1 if it is a non-repeating key.
When state 2 actually reaches a repeat, baby bottle it units the repeat time to 1/4 second from now. Task units that if acceptable. Suppose: – We’ve got another gadget sending two-byte readings from a sensor, at unpredictable intervals, and we deliver them in on a 6551 ACIA, with no handshaking, to be used by another process when wanted. Since my processing power was limited, and a few the tasks needed an even bigger share of it than others, I put their subroutine calls in the main loop twice every, distributed such that they would never have to wait too long between runs. In the event you do put it in RAM, the task at the top of the record ought to probably be the one which adjusts the record, including new duties or deleting ones which can be not needed. ROM, and the task list did not change; however you may put it in RAM on the 6502 if you like, and regulate the list as you add or take away duties. Task below is to be referred to as by major loop. EQ ; If it has, loop once more to repeat the method. MINUS ; If it’s damaging, we have not reached the repeat time but, so just exit.
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