Framebuffer

Driver for the BCM2837B0 (Raspberry Pi 3 B+) framebuffer. More...

Functions
void	drawChar (char c, int x, int y, ulong color)
void	drawPixel (int x, int y, ulong color)
void	drawLine (int x1, int y1, int x2, int y2, ulong color)
void	drawSegment (int x1, int y1, int x2, int y2, ulong color)
void	drawRect (int x1, int y1, int x2, int y2, ulong color)
void	fillRect (int x1, int y1, int x2, int y2, ulong color, bool gradient)
void	drawCircle (int x0, int y0, int radius, ulong color)
void	fillCircle (int x0, int y0, int radius, ulong color, bool gradient)
void	drawBody (int x0, int y0, int radius, ulong color)
void	fillBody (int x0, int y0, int radius, ulong color, bool gradient)
syscall	fbputc (uchar c, device *devptr)
syscall	fbgetc (device *devptr)
syscall	fbprintf (char *fmt,...)
devcall	fbPutc (device *devptr, char ch)
devcall	fbWrite (device *devptr, const uchar *buf, uint len)
ulong	mailboxRead ()
void	mailboxWrite (ulong data)
ulong	readMMIO (ulong base, ulong reg)
void	writeMMIO (ulong base, ulong reg, ulong val)
ulong	physToBus (void *address)
volatile unsigned int	__attribute__ ((aligned(16)))
void	screenInit ()
int	framebufferInit ()
void	screenClear (ulong color)
void	minishellClear (ulong color)
void	initlinemap ()
double	power (double base, int exp)
long	factorial (int num)
double	cosine_taylor (double x, int terms)
double	cos (int x)
double	sine_taylor (double x, int terms)

Detailed Description

Driver for the BCM2837B0 (Raspberry Pi 3 B+) framebuffer.

This driver communicates with the VideoCore GPU and provides functions to draw shapes and print text to the screen.

Function Documentation

volatile unsigned int __attribute__

(

(aligned(16))

)

Make a mailbox call.

Parameters

ch	Mailbox channel

Returns

::SYSERR on failure, non-zero on success

double cos

(

int

x

)

Compute the cosine using the Taylor approximation as a helper function

Parameters

x	Angle, in degrees

Returns

Double-precision result of the computation

double cosine_taylor	(	double	x,
		int	terms
	)

Compute the Taylor series approximation of cosine using power and factorial x Base value

Parameters

terms

Terms of the sum

Returns

Double-precision result of the cosine approximation

void drawBody	(	int	x0,
		int	y0,
		int	radius,
		ulong	color
	)

Turtle graphics specific circle functions

Parameters

x0	x-coordinate of circle center
y0	y-coordinate of circle center
radius	radius of circle
color	color of circle

void drawChar	(	char	c,
		int	x,
		int	y,
		ulong	color
	)

font.c includes a 12 byte representation of each of the first 128 ASCII characters. each byte is one row of 0's and 1's, where 1's represent that a pixel should be rendered in that location.

Parameters

c	character to be drawn
x	x-coordinate of character
y	y-coordinate of character
color	color of character

void drawCircle	(	int	x0,
		int	y0,
		int	radius,
		ulong	color
	)

Midpoint Circle Algorithm calculation of a circle. Based on "x^2 + y^2 = r^2"

Parameters

x0	x-coordinate of circle center
y0	y-coordinate of circle center
radius	radius of circle
color	color of circle

void drawLine	(	int	x1,
		int	y1,
		int	x2,
		int	y2,
		ulong	color
	)

Line drawing based on Bresenham's Algorithm. So that we don't need to mess with division or decimals.

Parameters

x1	starting x-coordinate of line
y1	starting y-coordinate of line
x2	ending x-coordinate of line
y2	ending y-coordinate of line
color	color of line

void drawPixel	(	int	x,
		int	y,
		ulong	color
	)

Draws a colored pixel at given (x, y) coordinates.

Parameters

x	x-coordinate of pixel
y	y-coordinate of pixel
color	color of pixel

void drawRect	(	int	x1,
		int	y1,
		int	x2,
		int	y2,
		ulong	color
	)

Draws a rectangle outline TODODC better description

Parameters

x1	upper left hand corner x-coordinate
y1	upper left hand corner y-coordinate
x2	lower right hand corner x-coordinate
y2	lower right hand corner y-coordinate
color	color of rectangle

void drawSegment	(	int	x1,
		int	y1,
		int	x2,
		int	y2,
		ulong	color
	)

Modified drawLine specifically for turtle graphics

Parameters

x1	starting x-coordinate
y1	starting y-coordinate
x2	ending x-coordinate
y2	ending y-coordinate
color	color of line

long factorial

(

int

num

)

Compute the factorial of an integer

Parameters

num	Integer to compute factorial operation on

Returns

Long integer result of the factorial operation

syscall fbgetc

(

device *

devptr

)

perform a synchronous kernel read

Parameters

*devptr

pointer to device on which to write character

Returns

character read on success, SYSERR on failure

syscall fbprintf	(	char *	fmt,
			...
	)

kernel printf: formatted, unbuffered output to framebuffer Akin to "kprintf" for the serial driver. Alternate: fprintf(FRAMEBUF, "string");

Parameters

*fmt	pointer to string being printed

Returns

OK on success

syscall fbputc	(	uchar	c,
		device *	devptr
	)

perform a synchronous character write

Parameters

*devptr	pointer to device on which to write character
c	character to write

Returns

c on success, SYSERR on failure

devcall fbPutc	(	device *	devptr,
		char	ch
	)

Write a single character to the framebuffer

Parameters

devptr	pointer to framebuffer device
ch	character to write

devcall fbWrite	(	device *	devptr,
		const uchar *	buf,
		uint	len
	)

Write a buffer of characters to the framebuffer.

Parameters

devptr	pointer to framebuffer device
buf	buffer of characters to write
len	number of characters to write from the buffer

Returns

The number of characters written, which may be less than len in the event of a write error; or ::SYSERR if an error occurred before any characters at all were written.

void fillBody	(	int	x0,
		int	y0,
		int	radius,
		ulong	color,
		bool	gradient
	)

Draws filled in circle

Parameters

x0	x-coordinate of circle center
y0	y-coordinate of circle center
radius	radius of circle
color	color of circle
gradient	true if circle has a gradient; false if not

void fillCircle	(	int	x0,
		int	y0,
		int	radius,
		ulong	color,
		bool	gradient
	)

Draws a filled in circle TODODC better description

Parameters

x0	x-coordinate of circle center
y0	y-coordinate of circle center
radius	radius of circle
color	color of circle
gradient	true if circle has a gradient; false if not

void fillRect	(	int	x1,
		int	y1,
		int	x2,
		int	y2,
		ulong	color,
		bool	gradient
	)

Draws a filled-in ractangle, given coordinates and colorization options

Parameters

x1	upper left hand corner x-coordinate
y1	upper left hand corner y-coordinate
x2	lower right hand corner x-coordinate
y2	lower right hand corner y-coordinate
color	color of rectangle
gradient	true if rectangle has a gradient; false if not

int framebufferInit

(

)

Initializes the framebuffer used by the GPU via the framebuffer mailbox.

Returns

::OK on success; ::SYSERR on failure.

void initlinemap

(

)

Clear the "linemapping" array used to keep track of pixels we need to remember

ulong mailboxRead

(

)

Read from mailbox one on channel one (GPU mailbox) Note: Data: first 28 bits. Channel: last 4 bits.

void mailboxWrite

(

ulong

data

)

Write to GPU mailbox.

Parameters

data	Data to write to the mailbox

void minishellClear

(

ulong

color

)

Clear the minishell window

Parameters

color

Color to paint the window upon clear

ulong physToBus

(

void *

address

)

Converts ARM physical addresses to ARM bus addresses. Separate function for legibility's sake. Rev 1 board GPU required bus addresses. Now deprecated.

Parameters

address

Physical address to convert

double power	(	double	base,
		int	exp
	)

Compute the double-precision result of a power operation

Parameters

base	Double-precision base value of operation
exp	Integer exponent to which the base is raised

Returns

Double-precision result of the power operation

ulong readMMIO	(	ulong	base,
		ulong	reg
	)

To omit illegible lines of code, a helper function that reads from memory mapped IO registers.

Parameters

base	Register base
reg	MMIO register to read

void screenClear

(

ulong

color

)

Very heavy handed clearing of the screen to a single color.

Parameters

color

void screenInit

(

)

Calls framebufferInit() several times to ensure we successfully initialize, just in case.

Returns

Void upon completion.

double sine_taylor	(	double	x,
		int	terms
	)

Compute the Taylor series approximation of sine

Parameters

x	Base value
terms	Terms of the sum

Returns

Double-precision result of the sine approximation

void writeMMIO	(	ulong	base,
		ulong	reg,
		ulong	val
	)

The opposite of above. Write to MMIO.

Parameters

base	Register base
reg	MMIO register to write to
val	Value to be written