I'm trying to write into an EEPROM via I²C from user space. I'm using the /dev device file and the open, read, write and ioctl functions. Reading works without a problem, but when I use the same code for writing (just replacing read with write), it fails. The EEPROM is not write protected (echoing into the device file of the EEPROM driver works).
The code I have is as follows.
if ((fd = open(write_destination, O_RDWR)) < 0) {
goto error;
}
if (ioctl(fd, I2C_SLAVE_FORCE, 0x50) < 0) {
goto error_fd;
}
while((n = write(fd, self->fields[i].buf, self->fields[i].size)) != self->fields[i].size)
perror("");
What am I overlooking?
Some EEPROMs only allow writing small amounts, then wait, and then write more. Check the datasheet to be sure. Also, I recommend to use a logic analyzer to check the correct commands are going to the I²C - I love the analyzer at www.salae.com.
Related
I have a STM32 Nucleo-64 development board with STM32L476RG MCU on it.. I have made a small PCB that, among other things, brings the USB interface to a connector.
I have followed the steps shown here: https://www.youtube.com/watch?v=rLnQ3W8gmjY
When I run the code in debug mode (in STM32CubeIDE v1.10.1) the USB never appears on my computer. I have also probed the USB data +/- signals and see no activity.
When I step through the code, I can see that something is failing immediately in:
MX_USB_DEVICE_Init()
USBD_Init()
The code the that fails is:
USBD_StatusTypeDef USBD_Init(USBD_HandleTypeDef *pdev,
USBD_DescriptorsTypeDef *pdesc, uint8_t id)
{
USBD_StatusTypeDef ret;
/* Check whether the USB Host handle is valid */
if (pdev == NULL)
{
#if (USBD_DEBUG_LEVEL > 1U)
USBD_ErrLog("Invalid Device handle");
#endif
return USBD_FAIL;
}
The exact line above that fails is if (pdev == NULL)
One thing to note is that the CubeMX tool did NOT add a handler declaration:
USBD_HandleTypeDef hUsbDeviceFS;
...despite me configuring up the USB interface... I added my own line in main.c:
extern USBD_HandleTypeDef hUsbDeviceFS;
..thinking it may be declared elsewhere??
Can someone please help me figure out whats going on?
Thanks!
Followed a video example online, but its not working as expected. I was expecting to see the dev board appear as a USB device on my computer and spit out some text.
I am unfamiliar with Linux kernel development but I'm tasked with updating a kernel driver so that it will return a status code that can be read by an application. This will require that the driver poll the hardware a couple of times a second to see what camera format is being sent (PAL, NTSC, or none).
However, I'm at a loss on how this would be accomplished. I understand how the driver communicates with the hardware, but I don't understand how to pass this data to the application. Does this type of behavior require the use of an ioctl() call or is this a read file operation? Also if the application is calling an IOCTL or read function and then needs to wait for the hardware to respond will this create a performance issue?
Also for added information, I am working on a 2.6 version of the kernel. I'm working my way through "Linux Device Drivers 3rd Ed", but nothing stands out on how to address this specific issue. LDD3 makes it sound like ioctl() only for sending commands to the driver. Since this is a V4L driver, open file will return image data, not the status information I want, I think.
I recommend checking the latest V4L2 API document, hosted on linuxtv.org: http://linuxtv.org/downloads/v4l-dvb-apis/
Userspace applications can call an IOCTL to query the current input format. The following userspace code can be used to query the kernel driver for the current video standard:
(quoting http://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html#standard)
Example 1.5. Information about the current video standard
v4l2_std_id std_id;
struct v4l2_standard standard;
if (-1 == ioctl (fd, VIDIOC_G_STD, &std_id)) {
/* Note when VIDIOC_ENUMSTD always returns EINVAL this
is no video device or it falls under the USB exception,
and VIDIOC_G_STD returning EINVAL is no error. */
perror ("VIDIOC_G_STD");
exit (EXIT_FAILURE);
}
memset (&standard, 0, sizeof (standard));
standard.index = 0;
while (0 == ioctl (fd, VIDIOC_ENUMSTD, &standard)) {
if (standard.id & std_id) {
printf ("Current video standard: %s\n", standard.name);
exit (EXIT_SUCCESS);
}
standard.index++;
}
/* EINVAL indicates the end of the enumeration, which cannot be
empty unless this device falls under the USB exception. */
if (errno == EINVAL || standard.index == 0) {
perror ("VIDIOC_ENUMSTD");
exit (EXIT_FAILURE);
}
I am using embedded Linux for the NIOS II processor and device tree. The GPIO functionality provides the ability to read and or write a single bit at a time. I have some firmware and PIOS that I want to read or write atomically by setting or reading all 32 bits at one time. It seems like there would be a generic device driver that if the device tree was given the proper compatibility a driver would exist that would allow opening the device and then reading and writing the device. I have searched for this functionality and do not find a driver. One existing in a branch but was removed by Linus.
My question is what is the Linux device tree way to read and write a device that is a general purpose 32 bit register/pio?
Your answer is SCULL
Character Device Drivers
You will have to write a character device driver with file operations to open and close a device. Read, write, ioctl, and copy the contents of device.
static struct file_operations query_fops =
{
.owner = THIS_MODULE,
.open = my_open,
.release = my_close,
.ioctl = my_ioctl
};
Map the address using iomem and directly read and write to that address using rawread and rawwrite. Create and register a device as follows and then it can be accessed from userspace:
register_chrdev (0, DEVICE_NAME, & query_fops);
device_create (dev_class, NULL, MKDEV (dev_major, 0), NULL, DEVICE_NAME);
and then access it from userspace as follows:
fd = open("/dev/mydevice", O_RDWR);
and then you can play with GPIO from userspace using ioctl's:
ioctl(fd, SET_STATE);
I want to implement the already defined system calls in PintOS ( halt(), create()...etc defined in pintos/src/lib/user/syscall.c ). The current system call handler in pintos/src/userprog/syscall.c does not do anything. How do I make a process that makes system calls. Further I need to myself add a few system calls. How do I proceed in that too. But first I need to implement the existing system calls.
The default implementation in pintos terminates the calling process.
goto this link.There is explanation on where to modify the code to implement the system calls.
The "src/examples" directory contains a few sample user programs.
The "Makefile" in this directory compiles the provided examples, and you can edit it compile your own programs as well.
This program/process when run will inturn make a system call.
Use gdb to follow the execution of one such program a simple printf statement will eventually call write system call to STDOUT file.
The link given also has pointers on how to run pintos on gdb, my guess is you are using either bochs or qemu.In any case just run the gdb once with a simple hello world program running on pintos.
This will give u an idea of how the system call is made.
static void
syscall_handler (struct intr_frame *f)// UNUSED)
{
int *p=f->esp;
switch(*p)
case *p=SYS_CREATE // NUMBER # DEFINED
const char *name=*(p+1); //extract the filename
if(name==NULL||*name==NULL)
exit(-1);
off_t size=(int32_t)*(p+2);//extract file size
f->eax=filesys_create(name,size,_FILE); //call filesys_create
//eax will have the return value
}
This is pseudo code for sys_create .. all file system related system call are very trivial,
Filesys realted system calls like open read write close needs you to translate file to their corresponding fd (file descriptor). You need to add a file table for each process to keep track this, this can either be preprocess data or a global data.(UR choice),
case (*p==SYS_WRITE)
{
// printf("wite syscall\n");
char *buffer=*(p+2);
unsigned size=*(p+3);
int fd=*(p+1);
// getiing the fd of specified file
struct file *fil= thread_current()->fdtable[fd];/ my per thread fdtable
if(fd==1) goto here;
if(is_directory(fil->inode)){
exit(-1);
goto done;
}
here:
if(buffer>=PHYS_BASE)exit(-1);
if(fd<0||fd>=128){exit(-1);}
if(fd==0){exit(-1);} // writing to STDIN
if(fd==1) //writing to STDOUT
{
int a=(int)size;
while(a>=100)
{
putbuf(buffer,100);
buffer=buffer+100;
a-=100;
}
putbuf(buffer,a);
f->eax=(int)size;
}
else
if(thread_current()->fdtable[fd]==NULL)
{f->eax=-1;}
else
{
f->eax=file_write(thread_current()->fdtable[fd],buffer,(off_t)size);
}
done: ;
}//printf("write");} /* Write to a file. */
Open - adds anew entry to fdtable and return the fd number u give to the file,
close - remove that entry from fd table
read - similar to write.
The process_create ,wait are not simple to implement...
Cheers :)
I am writing an UDP client/server programs in C on linux. The thing is that I must add connection check feature. in linux man pages i found example of udp client with this feature( http://www.kernel.org/doc/man-pages/online/pages/man3/getaddrinfo.3.html ). It uses write/read functions to check server response. I tried to apply it to my program, and it looks like this:
char *test = "test";
nlen = strlen(test) + 1;
if (write(sock, test, nlen) != nlen) { // socket with the connection
fprintf(stderr, "partial/failed write\n");
exit(EXIT_FAILURE);
}
nread = read(sock, buf, nlen);
if (nread == -1) {
perror("Connection");
exit(EXIT_FAILURE);
}
the problem is than than i execute program with this bit when server is on, it does nothing except reading input infinite time which it doesn't use too. I tried kill(getpid(), SIGHUP) interrupt, which i found other similar topic here, and shutdown(sock, 1), but nothing seems to work. Could you please tell me a way out how to stop the input read or any other possible option to check if udp server is active?
You should use asynchronous reading.
For this you must use the select() function from "sys/socket.h".
The function monitors the socket descriptor for changes without blocking.
You can find the reference for it here or here or by typing "man select" in your console.
There is an example here for Windows, but its usage is very similar to UNIX.