2010-03-07 09:51:16 gpio-sysfs read error
dee lock (SINGAPORE)
Message: 86919
hi
Any ideas on what prevents a program reading from gpio-sysfs? My app reports:
"read (3 4096) -> 2
/sys/devices/virtual/gpio/gpio17/value: No such file or directory
error: /sys/devices/virtual/gpio/gpio17/value: read failed"
However the GPIO sysfs interface was requested and is active:
"root:/> cat /sys/devices/virtual/gpio/gpio17/value
0"
Any ideas what might be causing this problem? I tried symlinking to the gpio-sysfs but I received the same No Such File error .
I wrote a small test program which can successfully read from gpio-sysfs using c routines (i.e. fopen).
Cheers,
-Dee.
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2010-03-07 10:00:36 Re: gpio-sysfs read error
Mike Frysinger (UNITED STATES)
Message: 86920
run your app through strace to see where the error is coming from
sysfs is a virtual file system ... you cant create files in there
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2010-03-13 21:59:46 Re: gpio-sysfs read error
dee lock (SINGAPORE)
Message: 87179
hi.
I still cannot one particular app to read from /sys/devices/virtual/gpio/
Anyone know why? My strace shows the following:
open("/sys/devices/virtual/gpio/gpio17/value", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=4096, ...}) = 0
close(3) = 0
open("/sys/devices/virtual/gpio/gpio17/value", O_RDONLY) = 3
lseek(3, 0, SEEK_END) = 4096
lseek(3, 0, SEEK_SET) = 0
read(3, "0\n"..., 4096) = 2
write(2, "read ("..., 6read () = 6
write(2, "3"..., 13) = 1
write(2, " "..., 1 ) = 1
write(2, "4096"..., 44096) = 4
write(2, ") -> "..., 5) -> ) = 5
write(2, "2"..., 12) = 1
write(2, "\n"..., 1
) = 1
write(2, "/sys/devices/virtual/gpio/gpio17/"..., 38/sys/devices/virtual/gpio/gpio17/value) = 38
write(2, ": "..., 2: ) = 2
write(2, "No such file or directory"..., 25No such file or directory) = 25
write(2, "\n"..., 1
) = 1
close(3) = 0
write(2, "error: "..., 7error: ) = 7
write(2, "/sys/devices/virtual/gpio/gpio17/"..., 38/sys/devices/virtual/gpio/gpio17/value) = 38
write(2, ": read failed"..., 13: read failed) = 13
write(2, "\n"..., 1
)
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2010-03-14 10:55:40 Re: gpio-sysfs read error
Mike Frysinger (UNITED STATES)
Message: 87182
looks like your code is wrong then. the syscalls arent returning errors.