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2016-10-27T16:02:57Z

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Harald: /* Playing a file */

2009-03-11T12:05:22Z

‎Playing a file

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== Test Environments ==

{| class="smalldiv"
| style="background-color:#F6F9ED" |
| style="background-color:#F6F9ED" | Hardware Comments
| style="background-color:#F6F9ED" | '''Nut/OS 4.7.4'''
| style="background-color:#F6F9ED" | '''Nut/OS 4.8.0'''
|-
| Ethernut 3.0 E
| requires [http://www.ethernut.de/en/hardware/medianut2/index.html Medianut]
| Compiler Error
| NT
|-
| EIR 1.0 C
|
| OK [http://ethernut.de/arc/WIKI_BINARIES_ZIPPED/mp3-player-EIR1C-nutos-4.7.4.zip '''Binaries''']
|
|-
| AT91SAM7X-EK
| requires [http://www.ethernut.de/en/documents/sam-web-radio.html Calypso]
| NT
| NT
|-
| AT91SAM9260-EK
| requires [http://www.ethernut.de/en/documents/sam-web-radio.html Calypso]
| NT
| NT
|-
| id="compilertd" colspan="4" |'''Compiler:''' ARM-GCC 4.2.2
|}

== Description ==

This is a simple MP3 player. It scans a MultiMedia Card for files with extension <code>.mp3</code> and sends the contents to an MP3 decoder.

== Source Code ==

This code requires Nut/OS 4.8 or later. Check the page's history (Nov 2008) for previous versions.

=== Main routine ===

The main program does some initialization and then enters an endless loop, reading the MMC.

<source lang="c">
#include <cfg/os.h>

#include <fs/phatfs.h>
#include <sys/timer.h>
#include <dev/board.h>

#include <cfg/arch/gpio.h>
#include <cfg/audio.h>

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
#include <dirent.h>

#define VERSION "1.4.1"

#if defined(AT91SAM7X_EK) || defined(AT91SAM9260_EK)
#include <dev/hxcodec.h>
#else
#define CS_HARDWARE_CODEC 1
#include <dev/vscodec.h>
#endif

static int ScanFolder(char *root);
static int PlayFile(int fd);

int main(void)
{
u_long baud = 115200;
int volid;

NutRegisterDevice(&DEV_DEBUG, 0, 0);
freopen(DEV_DEBUG_NAME, "w", stdout);
_ioctl(_fileno(stdout), UART_SETSPEED, &baud);
puts("\nNut/OS MMC MP3 Player " VERSION);

#ifdef CS_HARDWARE_CODEC
NutRegisterSpiDevice(&devSpiVsCodec0, &DEV_SPIBUS, CS_HARDWARE_CODEC);
#else
NutRegisterDevice(&devHelixCodec, 0, 0);
#endif
NutRegisterDevice(&devPhat0, 0, 0);
NutRegisterDevice(&DEV_MMCARD, 0, 0);

for (;;) {
for (;;) {
printf("Card...");
if ((volid = _open(DEV_MMCARD_NAME ":1/PHAT0", _O_RDWR | _O_BINARY)) != -1) {
puts("ready");
break;
}
puts("not found");
NutSleep(2000);
}
ScanFolder("PHAT0:/");
_close(volid);
}
return 0;
}
</source>

At the top all required header files are included.

The MP3 Player can either use a hardware decoder chip or do decoding by software.

=== Scanning a folder ===

The following routine scans a specified folder for MP3 files.

<source lang="c">
static int ScanFolder(char *root)
{
int rc = 0;
DIR *dir;
int fd;
char *path;

printf("Scanning %s\n", root);
dir = opendir(root);
if(dir) {
struct dirent *dep;

path = malloc(256);
while(rc == 0 && (dep = readdir(dir)) != NULL) {
if (strcmp(dep->d_name, ".") && strcmp(dep->d_name, "..")) {
if (dep->d_type) {
strcpy(path, root);
strcat(path, dep->d_name);
strcat(path, "/");
rc = ScanFolder(path);
} else {
char *cp = strrchr(dep->d_name, '.');
if (cp && stricmp(cp, ".mp3") == 0) {
strcpy(path, root);
strcat(path, dep->d_name);
sprintf(path, "%s%s", root, dep->d_name);
printf("Playing %s\n", path);
fd = _open(path, _O_RDONLY | _O_BINARY);
if (fd == -1) {
rc = -1;
} else {
rc = PlayFile(fd);
_close(fd);
}
}
}
}
}
closedir(dir);
free(path);
}
return rc;
}
</source>

=== Playing a file ===

The routine PlayFile expects a file handle of an opened MP3 file and streams its contents to the audio decoder driver.

<source lang="c">
static int PlayFile(int fd)
{
int codec;
uint8_t *mp3buff;

codec = _open("audio0", _O_WRONLY | _O_BINARY);
if (codec == -1) {
printf("No codec\n");
return -1;
}

mp3buff = malloc(512);
for (;;) {
int got;
uint8_t *bp;

bp = mp3buff;
got = _read(fd, bp, 512);
if (got <= 0) {
break;
}
while (got) {
int sent;

sent = _write(codec, bp, got);
if (sent < 0) {
break;
}
if (sent == 0) {
NutSleep(1);
} else {
got -= sent;
bp += sent;
}
}
}
free(mp3buff);
_close(codec);

return 0;
}
</source>

=== Makefile ===

Here's the Makefile to build the MP3 player.
Note, that the spaces before <code>-rm -f $...</code> have to be tabs instead of spaces.

<source lang="text">
PROJ = cs_mp3mmc

include ../Makedefs

SRCS = $(PROJ).c
OBJS = $(SRCS:.c=.o)
LIBS = $(LIBDIR)/nutinit.o -lnutfs -lnutos -lnutcrt -lnutdev -lnutarch -lnutcontrib
TARG = $(PROJ).hex

all: $(OBJS) $(TARG) $(ITARG) $(DTARG)

include ../Makerules

clean:
-rm -f $(OBJS)
-rm -f $(TARG) $(ITARG) $(DTARG)
-rm -f $(PROJ).obj
-rm -f $(PROJ).map
-rm -f $(SRCS:.c=.lst)
</source>

== See also ==

* [[Reading PHAT Files]]
* [[Reading PHAT Directories]]
* More [[Nut/OS Examples]]

== External Links ==

* [http://en.wikipedia.org/wiki/Fopen C file input/output] The C programming language provides many standard library functions for file input and output.
* [http://en.wikipedia.org/wiki/MP3 MP3] MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a digital audio encoding format using a form of lossy data compression.

[[Category:Code Snippets]]

 
{{Languages}}

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