Hi ,
In my embedded linux-arm target , in a userspace thread , i am reading
hid events over usb-hiddev interface (/dev/hiddev) .
basically what i do is this :
read_thread(){
while(1){
ret = read( "/dev/hiddev" , user_buffer , bytes_to_read);
printf("bytes received =%d" , ret ) ; // (printf prints debug message
to serial console );
}
}
now whenever i use the printf statement in read thread , kernel space
ring buffer in usb-hid driver is overrun frequently , which results
in loss of data send by usb device .
if i remove printf in read thread , no overruns are reported in
usb-hid driver . that means if printf is used , application
read_thread is not able to
read data in time which leads to driver ring buffer overrun .
does this behaviour of printf points to some problem in embedded
linux's scheduler ( printf prints data to debug serial port , and
consecutive read() calls in read_thread() are scheduled lately due
to that ) ?
do the actual implementation of printf involves any kind of sleeps ?
kindly share necessary insight wrt above printf usage and driver ring
buffer overrun .
regards
Amit Nagal
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