Reverse Module What if we give the CPU priority over the DMA on accessing the bus?
Both the DMA module and the processor access the system bus to transfer data to and from the memory. Typically, the DMA module is given priority in accessing the bus, i.e. it can "steal" a bus cycle from the processor. What would be the advantage and the disadvantage of reversing this, i.e. giving the processor priority over the DMA module when accessing the system bus?
DMA gives a device direct access to the memory.
If you give the processor priority over DMA then you are putting the devices that use it "back in line" to go through the processor to access memory.
Since that is the normal procedure, I see no benefit in doing so. Essentially you should get the same effect by just removing DMA completely.
It would also greatly increase the load on the processor.
See this article for more information.
A Solar Charge Controller is an essential part of nearly all power systems that charge batteries, whether the power source is PV, wind, hydro, fuel, or utility grid. Its purpose is to keep your batteries properly fed and safe for the long term. The fundamental functions of a controller are quite simple. Charge controllers chunk reverse current and prevent battery swindle. Some controllers also prevent battery overdischarge, protect from electrical overload, and/or display battery status and the flow of power. Let's examine each function individually.
Jamming overturn Current:
Solar Photo Voltaic Module work by pumping current through your battery in one direction. At night, the panels may pass a bit of current in the reverse direction, causing a slight discharge from the battery. The potential loss is slight, but it is easy to prevent. Some types of wind and hydro generators also draw reverse current when they stop. In most controllers, charge current passes through a semiconductor which acts like a valve to control the current. It is called a "semiconductor" because it passes current only in one direction. It prevents reverse current without any extra effort or cost. In some controllers, an electromagnetic coil opens and closes a mechanical switch. This is called a relay. The relay switches off at night, to block reverse current. If you are using a PV array only to trickle-charge a battery, then you may not need a charge controller. This is a rare application. An example is a tiny maintenance module that prevents battery discharge in a parked vehicle but will not support significant loads. You can install a simple diode in that case, to block reverse current. A diode used for this purpose is called a blocking diode .
Stopping Overcharge:
When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads or cause your inverter to shut off. Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called "voltage regulating." It is the most essential function of all charge controllers. The controller "looks at" the voltage, and regulates the battery charging in response. Some controllers regulate the flow of energy to the battery by switching the current fully on or fully off. This is called "on/off control." Others reduce the current gradually. This is called "pulse width modulation. Both methods work well when set properly for your type of battery. A Solar Charge Controllers holds the voltage more constant. If it has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a "finish" or "trickle" charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy. It maintains a full charge but minimizes water loss and stress. The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery. The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do not.
Manage Set Points vs. Temperature:
The ideal set points for charge control vary with a battery's temperature. Some controllers have a feature called "temperature compensation." When the controller senses a low battery temperature, it will raise the set points. Otherwise when the battery is cold, it will reduce the charge too soon. If your batteries are exposed to temperature swings greater than about 17degrees c, compensation is essential. Some controllers have a temperature sensor built in. Such a controller must be mounted in a place where the temperature is close to that of the batteries. Better controllers have a remote temperature probe, on a small cable. The probe should be attached directly to a battery in order to report its temperature to the controller. An alternative to automatic temperature compensation is to manually adjust the set points (if possible) according to the seasons. It may be sufficient to do this only twice a year, in spring and autumn.
Manage Set Points vs. Battery Type:
The ideal set points for charge controlling depend on the design of the battery. The vast majority of renewable energy systems use deep-cycle lead-acid batteries of either the flooded type or the sealed type. Flooded batteries are filled with liquid. These are the standard, economical deep cycle batteries. Sealed batteries use saturated pads between the plates. They are also called "valve-regulated" or "absorbed glass mat," or simply "maintenance-free." They need to be regulated to a slightly lower voltage than flooded batteries or they will dry out and be ruined. Some controllers have a means to select the type of battery. Never use a controller that is not intended for your type of battery.
