New answers tagged 6502
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Not really an answer, but...
...The phrase "co-processor," can mean two different things.
When you're talking about a "floating point co-processor" or "FPU," you're probably talking about a chip that extends the capabilities of the main CPU. In a very real sense, it becomes part of the CPU when it is installed. It adds ...
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Broadly speaking, all these systems worked in the same way. The base system is always the same, generate the lines and synchronisation pulses needed to build display frames.
The video circuit (could be a single chip or not) knows when it starts a single frame, and has somewhere access to memory (which can be private or shared with the microprocessor). It ...
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A standalone processor, such as the ones you have listed, would usually only be able to perform some basic operations on integer data. This would typically be add and subtract because those operations can be trivially implemented with minimal amounts of logic (see Ben Eater's series on building a CPU on a breadboard as an example).
Earlier versions of the ...
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The video circuitry was a lot simpler in those days and there was no true GPU as we have today. The video memory was part of the CPU memory space and any video circuitry merely converted it into a video signal. There was no graphics processing outside of what the CPU did.
Some, particularly earlier systems use discrete components to produce a simple video ...
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While many of the performance capabilities of modern desktop processors intended to run multi-tasking operating systems are somewhat wasted in a real time context, they are not actually impediments.
A soundly designed real time operating system uses hardware timers for the precise timing needs in terms of scheduling when code runs. Desktop operating systems ...
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There are three principal reasons:
1: Realtime software demands CPUs whose execution time is highly predictable. That is true mostly of CPUs without speculative features such as caching and dynamic branch prediction. Some modern CPUs (eg. ARM Cortex-R series) are specifically designed to provide this property.
2: Low interrupt latency and overhead, on the ...
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This paragraph in Wikipedia really is no candidate for the best entry-of-the-year award. It seems to be comparing Apples with Oranges. (Or rather starts talking about CPUs, then commences on PCs vs. "something else", i.e. system architecture). A comparison of interrupt latency and predictability thereof doesn't make much sense on CPU level - It ...
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It's the simplicity.
Under modern general purpose operating systems, you don't usually have hard real-time guarantees. Too many things are going on. Context switching is slow. Interrupts are slow. The kernel is often not fully pre-emptable.
On top of all that, modern hardware incorporates features like speculative execution, extensive pipelining, ...
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On a typical 6502, Z80, or 68000 system, it's possible to predict very precisely exactly how long a piece of code will take to execute. The same is true, incidentally, of many small microcontrollers produced today. In many cases, this allows some operations to be done more efficiently than would otherwise be possible.
For example, if both function-control ...
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