Mirrors_Framework/fifofast
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Fix readme (whitespace and formatting)

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nqtronix
2018-11-10 08:52:45 +01:00
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commit e86e142d35
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README.md
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@@ -4,12 +4,12 @@
<h3 align="center" style="font-weight: bold; margin-top: 20px; margin-bottom: 20px;">A fast, generic fifo for MCUs.</h4>
<p align="center">
<a href="#changelog"><img src="https://img.shields.io/github/release-pre/nqtronix/fifofast.svg" alt="release: NA"></a>
<a href="#about"><img src="https://img.shields.io/badge/language-C_(GCC_5.4.0)-blue.svg" alt="language: C GCC (5.4.0)"></a>
<a href="#about"><img src="https://img.shields.io/badge/platform-MCUs, AVR8-blue.svg" alt="platform: MCUs, AVR8"></a>
<a href="#about"><img src="https://img.shields.io/badge/status-active-brightgreen.svg" alt="status: active"></a>
<a href="https://github.com/nqtronix/fifofast/issues"><img src="https://img.shields.io/github/issues/nqtronix/fifofast.svg" alt="issues: NA"></a>
<a href="#license"><img src="https://img.shields.io/github/license/nqtronix/fifofast.svg" alt="license: NA"></a>
<a href="#changelog"><img src="https://img.shields.io/github/release-pre/nqtronix/fifofast.svg" alt="release: NA"></a>
<a href="#about"><img src="https://img.shields.io/badge/language-C_(GCC_5.4.0)-blue.svg" alt="language: C GCC (5.4.0)"></a>
<a href="#about"><img src="https://img.shields.io/badge/platform-MCUs, AVR8-blue.svg" alt="platform: MCUs, AVR8"></a>
<a href="#about"><img src="https://img.shields.io/badge/status-active-brightgreen.svg" alt="status: active"></a>
<a href="https://github.com/nqtronix/fifofast/issues"><img src="https://img.shields.io/github/issues/nqtronix/fifofast.svg" alt="issues: NA"></a>
<a href="#license"><img src="https://img.shields.io/github/license/nqtronix/fifofast.svg" alt="license: NA"></a>
</p>
<p align="center">
@@ -61,20 +61,20 @@ _fff_declare(int8_t, fifo_int8, 16);
int main(void)
{
// volatile prevents the compiler from optimizing the variable away
volatile int8_t tmp;
// volatile prevents the compiler from optimizing the variable away
volatile int8_t tmp;
// initialize fifo
_fff_init(fifo_int8);
// write a value to the fifo
_fff_write(fifo_int8, -42);
// write a value to the fifo
_fff_write(fifo_int8, -42);
// read back the value from the fifo
tmp = _fff_read(fifo_int8);
// read back the value from the fifo
tmp = _fff_read(fifo_int8);
// 'tmp' contains now the value '-42'
while(1);
// 'tmp' contains now the value '-42'
while(1);
}
```
@@ -229,33 +229,36 @@ To use **fifofast** you don't need to know its inner workings. This chapter is f
### The Typical Implementation
To get the best performance most fifos are based on an array for data storage. New elements are always placed at the next free index. When the fifo is read, the element of the earliest written index is returned. Example:
empty array:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ │ │ │ │ │ │ │ │
└───┴───┴───┴───┴───┴───┴───┴───┘
```
empty array:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ │ │ │ │ │ │ │ │
└───┴───┴───┴───┴───┴───┴───┴───┘
write 4 elements:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ a │ b │ c │ d │ │ │ │ │
└───┴───┴───┴───┴───┴───┴───┴───┘
read 2 elements:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ │ │ c │ d │ │ │ │ │
└───┴───┴───┴───┴───┴───┴───┴───┘
write 4 elements:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ a │ b │ c │ d │ │ │ │ │
└───┴───┴───┴───┴───┴───┴───┴───┘
read 2 elements:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ │ │ c │ d │ │ │ │ │
└───┴───┴───┴───┴───┴───┴───┴───┘
```
After the array was filled at least once, new data must be added to the very first location. This is called a [circular buffer (wiki)][wiki-circular-buffer]
after some time (example):
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ │ │ │ │ │ e │ f │ g │
└───┴───┴───┴───┴───┴───┴───┴───┘
```
after some time (example):
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ │ │ │ │ │ e │ f │ g │
└───┴───┴───┴───┴───┴───┴───┴───┘
write 1 element:
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ h │ │ │ │ │ e │ f │ g │
└───┴───┴───┴───┴───┴───┴───┴───┘
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ h │ │ │ │ │ e │ f │ g │
└───┴───┴───┴───┴───┴───┴───┴───┘
```
To detect this overflow the straight forward approach is to use `if(index > array_size){index = 0;}`. This comparison has to be done for _every_ fifo access. Branches take typically more cycles than arithmetic instruction, especially if a [instruction pipeline (wiki)][wiki-pipelining] is used within the MCU.