ac97.c File Reference

AC'97 audio demo. More...

#include <Uefi.h>
#include <Library/UefiLib.h>
#include <Library/ShellCEntryLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <UEFIStarter/core.h>
#include <UEFIStarter/ac97.h>
#include <UEFIStarter/pci.h>

Macros
#define	SAMPLES_PER_BUFFER   10000
	Number of samples to use in each buffer. More...
#define	SAMPLES_FREQ(FREQ)   ((tc%(FREQ))*60000/(FREQ)-30000)
	Shortcut macro to sample a (non-harmonic) frequency. More...

Functions
void	fill_buffers_crossscale (ac97_buffers_s16_t *buffers, unsigned int start_buffer, unsigned int buffer_count, unsigned int loop_offset)
	Fills audio buffers with scales, one channel going down, the other channel going up. More...
void	fill_buffers_harmonic_scale (ac97_buffers_s16_t *buffers, unsigned int start_buffer, unsigned int buffer_count)
	Fills audio buffers with harmonic scales. More...
void	output_audio (ac97_handle_t *handle)
	Fills audio buffers with scales, copies buffers to AC'97 device and starts playback. More...
void	loop_civ (ac97_handle_t *handle)
	This fills audio buffers while they're being played. More...
EFI_STATUS	run_audio_stuff (EFI_PCI_IO_PROTOCOL *audio)
	Handles entire lifetime of AC'97 audio output. More...
INTN EFIAPI	ShellAppMain (UINTN argc, CHAR16 **argv)
	Main function, gets invoked by UEFI shell. More...

Detailed Description

AC'97 audio demo.

Author

Richard Nusser

Copyright

2017-2018 Richard Nusser

License

GPLv3 (see http://www.gnu.org/licenses/)

See also

https://github.com/rinusser/UEFIStarter

Warning

This application accesses your audio hardware directly, take care about the sound volume in particular. A volume of 100% (the maximum) will set your master and PCM OUT volumes to 100%. If you're running this on hardware directly (because you e.g. booted a computer into this environment), this means the sound volume will be as high as it can possibly go (apart from vendor-specific additional volume boosts). Depending on your audio setup this may even cause damage to your amplifier, speakers or hearing: reduce any attached devices' (e.g. speakers') volumes before starting this application. If you're running this in a virtual environment, e.g. VirtualBox, this will output at 100% of the hypervisor's volume.

Macro Definition Documentation

SAMPLES_PER_BUFFER

#define SAMPLES_PER_BUFFER   10000

Number of samples to use in each buffer.

Determines length of individual notes (thus speed of playback). Keep this value below 32767.

SAMPLES_FREQ

#define SAMPLES_FREQ

(

FREQ

)

((tc%(FREQ))*60000/(FREQ)-30000)

Shortcut macro to sample a (non-harmonic) frequency.

Parameters

FREQ	the frequency to use (of no particular unit)

Returns

the generated sample

Function Documentation

fill_buffers_crossscale()

void fill_buffers_crossscale	(	ac97_buffers_s16_t *	buffers,
		unsigned int	start_buffer,
		unsigned int	buffer_count,
		unsigned int	loop_offset
	)

Fills audio buffers with scales, one channel going down, the other channel going up.

Does not use the harmonic scale: this will sound bad.

Parameters

buffers	the AC'97 buffer list to fill
start_buffer	index of the first buffer to fill
buffer_count	the number of buffers to fill
loop_offset	offset for loop counter, the higher this is the higher the generated notes will be

fill_buffers_harmonic_scale()

void fill_buffers_harmonic_scale	(	ac97_buffers_s16_t *	buffers,
		unsigned int	start_buffer,
		unsigned int	buffer_count
	)

Fills audio buffers with harmonic scales.

Parameters

buffers	the audio buffers to write to
start_buffer	index of the first buffer to fill
buffer_count	number of buffers to fill

output_audio()

void output_audio

(

ac97_handle_t *

handle

)

Fills audio buffers with scales, copies buffers to AC'97 device and starts playback.

This is pretty much how you'd output prepared audio, e.g. when playing music.

Start the application with -trace to see when playback switches to the next buffer.

Parameters

handle

the AC'97 handle to use

loop_civ()

void loop_civ

(

ac97_handle_t *

handle

)

This fills audio buffers while they're being played.

This is how you'd output audio on the fly, e.g. sound effects that depend on user inputs.

Seems like the timer granularity can't be decreased much, setting it to e.g. 5ms loses count of a few ticks.

Parameters

handle

the AC'97 handle to use

run_audio_stuff()

EFI_STATUS run_audio_stuff

(

EFI_PCI_IO_PROTOCOL *

audio

)

Handles entire lifetime of AC'97 audio output.

This shows the high-level interface to the AC'97 library: find the audio device, initialize the handle, configure audio output, fill buffers, start playback and finally close the handle.

Parameters

audio

the UEFI PCI I/O protocol for the AC'97 chipset

Returns

the resulting status, EFI_SUCCESS if everything went OK

ShellAppMain()

INTN EFIAPI ShellAppMain	(	UINTN	argc,
		CHAR16 **	argv
	)

Main function, gets invoked by UEFI shell.

Parameters

argc	the number of command-line arguments passed
argv	the command-line arguments passed

Returns

an EFI status code for the shell