If a process gets really advanced, this technique of routing execution to the correct part of the duty each time it is called could get a bit bushy if you actually needed to keep away from all pointless delays. I usually use a CASE statement (known as “Select CASE” in Basic and “change” in C, however I named many of my structure macros after Forth structures) to steer the execution to the suitable part of the routine relying on the state. There is not any need for key-up debouncing, LDA KEY ; as state zero will do the same thing. LDA KEY ; Here we have reached the tip of the debounce interval with the key still pressed. LDA VIA1T1CL ; Clear VIA1 interrupt. The tasks I had were all dependent to some extent on time, or on different 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 the duty was energetic on the time, or one thing like that; so each one might: 1. Check to see if it is even alleged to be energetic in the intervening time. Such a activity might first test a flag variable to see if it’s even presupposed to be active at the moment, and if not, return immediately.
For less runtime overhead, it may be higher to have the alarm set up routine see if there’s already an alarm with the same due time, and if that’s the case, increment the following one by a tick (or much more if there’s any threat that a single tick will not give the last earlier alarm time to complete executing first). SCAN ; See if it is still being pressed. Have the true-time clock ISR watch for the subsequent alarm being past due, quite than limiting it to an exact match. LOOP. The state quantity is held in the variable, and will depend on what the duty was doing final, and may get modified (“transitioned” to another state) when it has completed one thing, or when an event or clock time that it was awaiting arrives, dictating that we’re transferring on to the following step, or maybe to start out over. The translation will not be examined, baby bottle but provides you with a good head start while you need to write down code for this kind of thing. I’ve completed an analogous thing with an LED the place the first indication comes when there’s one-third of the battery life left, and the blink rate will increase because the battery voltage continues to drop, giving a reasonably good idea of how much life is left.
5×7 dot matrix. A custom character of a battery works out nicely. As you might think about, there are many ways to perform alarm strategies. A transition usually consists of incrementing the state to the following greater quantity; however there are plenty of exceptions the place it could get changed to something else. If there is at the least one alarm pending, it should often take three extra instructions. If there’s a danger of getting a number of alarms with the very same due time, a couple of possible methods to deal with it are: – Have the actual-time clock ISR check for more presumably due alarms after executing the first one. Comparison is finished on the low byte first and excessive byte final to avoid wasting cycles, for the reason that high bytes usually tend to be the identical. You may select which bytes of the RTC to make use of, e.g., bytes 0 and 1, 1 and 2, or 2 and 3.) The goal worth ought to be initialized within the reset routine to prevent tremendous lengthy delays before the first blink, if the icon ought to blink.
Take for instance a key-scanning routine. Many duties may have little or nothing to do most of the instances they’re called, so that they take little or no time. If there’s no alarm pending, the RTC NMI ISR will usually take eight directions, including the RTI. All the time it takes then is simply the JSR, BIT, BMI, RTS, solely 18 clocks, including the JSR and RTS. 32 ; alarm. If it doesn’t match (as will nearly always be BNE CkAlmEnd ; the case), then simply exit. 1 ; If there isn’t any alarm pending (shown by a 0 in the high BEQ CkAlmEnd ; byte of the addr of its routine, then just exit. Then I was ready to make use of the workbench computer for something else at the same time, with my different program not having to understand it wasn’t the just one operating. You might have routines to: – set an alarm with an absolute time; – one other to set an alarm with a time relative to proper now; – sort alarms by chronological order (which would be used by the two above) and depart the following-due one at the head of the queue; – delete an alarm, using its execute tackle to search out the appropriate one, and close up the hole within the alarm record; – delete the alarm at the pinnacle of the queue (used particularly by that alarm when it executes); – learn the way long before the next alarm is due; and – do conversions from HH:MM:SS to centiseconds (or milliseconds, or whatever you employ) and back.
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