I am trying to write a function called SerialSend that will print the contents of a ring buffer (named testbuff) to my console.This is my definition for SerialSend.
void SerialSend (USInt* pusiBuffer, UDInt len, UDInt connectionId)
{
USART_WriteByte(DEMO_USART, testbuff[i]);
i++;
i %= DEMO_RING_BUFFER_SIZE;
}
When called, SerialSend is printing the first character in testbuff. How do I get it to print the rest of the contents of the buffer? This is the code in main where I call SerialSend and the break isn't working.
while(i<17)
{
SerialSend(testbuff, 17, 0) //Sends contents of testbuff to print in console
if (i==16)
{
break; //Break isn't working, probably because i never hits 16 due to the ring
}
}
It turns out that I had my ring buffer size too small, so I increased the size to 50 and editted the call in main like this:
while(1)
{
SerialSend(testbuff, 50, 0); //Sends contents of testbuff to print in console
if (i==17)
{
break;
}
}
The testbuff buffer holds 17 characters I want to print, hence the if statement for a break when the index hits the end of the message.
Related
I am attempting to write a bittorrent client. In order to parse the file etc. I need to read a torrent file into memory. I have noticed that fread is not reading the entire file into my buffer. After further investigation it appears that whenever the symbol shown below is encountered in the file, fread stops reading the file. Calling the feof function on the FILE* pointer returns 16 indicating that the end of file has been reached. This occurs no matter where the symbol is placed. Can somebody explain why this happens and any solutions that may work.
The symbol is highlighted below:
Here is the code that does the read operation:
char *read_file(const char *file, long long *len){
struct stat st;
char *ret = NULL;
FILE *fp;
//store the size/length of the file
if(stat(file, &st)){
return ret;
}
*len = st.st_size;
//open a stream to the specified file
fp = fopen(file, "r");
if(!fp){
return ret;
}
//allocate space in the buffer for the file
ret = (char*)malloc(*len);
if(!ret){
return NULL;
}
//Break down the call to fread into smaller chunks
//to account for a known bug which causes fread to
//behave strangely with large files
//Read the file into the buffer
//fread(ret, 1, *len, fp);
if(*len > 10000){
char *retTemp = NULL;
retTemp = ret;
int remaining = *len;
int read = 0, error = 0;
while(remaining > 1000){
read = fread(retTemp, 1, 1000, fp);
if(read < 1000){
error = feof(fp);
if(error != 0){
printf("Error: %d\n", error);
}
}
retTemp += 1000;
remaining -= 1000;
}
fread(retTemp, 1, remaining, fp);
} else {
fread(ret, 1, *len, fp);
}
//cleanup by closing the file stream
fclose(fp);
return ret;
}
Thank you for your time :)
Your question is oddly relevant as I recently ran into this problem in an application here at work last week!
The ASCII value of this character is decimal 26 (0x1A, \SUB, SUBSTITUTE). This is used to represent the CTRL+Z key sequence or an End-of-File marker.
Change your fopen mode ("In [Text] mode, CTRL+Z is interpreted as an end-of-file character on input.") to get around this on Windows:
fp = fopen(file, "rb"); /* b for 'binary', disables Text-mode translations */
You should open the file in binary mode. Some platforms, in text (default) mode, interpret some bytes as being physical end of file markers.
You're opening the file in text rather than raw/binary mode - the arrow is ASCII for EOF. Specify "rb" rather than just "r" for your fopen call.
I am making a simple Led program that will be turned into a library for my project. I have created four methods that will allow you to A) Setup as many Led pins as you want and make them as Outputs. B) Flash the Led lights at a customized time. C) Turn On Leds. D) Turn Off Leds. Everything is working if i just run the methods in the void loop(). For example:
Void loop(){
flashLed(pinNum, 2000);
turnOf(pinNum);
turnOn(pinNum);
}
If i run the above code it works fine, however it keeps looping as its obviously in a loop. So i decided to start the serial com by using Serial.begin(9600) in the setup(), and then testing for the serial com and used a switch case statement in order to appropriately implement these methods. What am i doing wrong here? i get no errors at all. When i type into the serial monitor nothing happens, i believe my logic is fine but that is why i am here. When anything is typed into the serial monitor, the code runs the default in the switch case statement and that is all. I have tried using while, if to no avail. Also tested the inverse of serial which would be !serial.available() Here is my code:
//Define the pin numbers
byte pinNum[] = {4, 3, 2};
void setup() {
//Setup the ledPins
ledSetup(pinNum);
Serial.begin(9600);
}
void loop() {
while(Serial.available() > 0){
//Read the incoming byte
byte ledStatus = Serial.read();
switch (ledStatus){
case 0:
turnOff(pinNum);
Serial.println("The Leds Have Been Turned Off");
break;
case 1:
turnOn(pinNum);
Serial.println("The Leds Have Been Turned On");
break;
case 2:
flashLed(pinNum, 1000); //This will make the Led blink for half a second
Serial.println("The Leds Will Begin Flashing");
break;
default:
flashLed(pinNum, 1000); //This will make the Led blink for half a second
break;
}
}
}
//Method to declare the pins as output
void ledSetup(byte ledPins[]){
for (int i = 0; i <= sizeof(ledPins); i++){
pinMode(ledPins[i], OUTPUT);
}
}
//Method to blink the Led light/lights
void flashLed(byte ledBlink[], int duration){
//Time is divided by two because it takes 2 seconds
//to run the sketch
for (int i = 0; i <= sizeof(ledBlink); i++){
digitalWrite(ledBlink[i], HIGH);
delay(duration/2);
digitalWrite(ledBlink[i], LOW);
delay(duration/2);
}
}
//Method to turn Leds off
void turnOff(byte ledOff[]){
for(int i = 0; i <= sizeof(ledOff); i++){
digitalWrite(ledOff[i], LOW);
}
}
//Method to turn Leds On
void turnOn(byte turnOn[]){
for (int i = 0; i <= sizeof(turnOn); i ++){
digitalWrite(turnOn[i], HIGH);
}
}
The serial monitor sends symbols encoded in the ASCII format.
e.g. when you enter 0, Serial.read() returns 48, which is the ASCII code for digit 0. Since the value 48 is not listed in the following cases, the default branch is taken:
case 0: ...
case 1: ...
case 2: ...
default: ...
There are many solutions to your problem.
1. change case conditions to match what you are sending:
case '0': ...
case '1': ...
case '2': ...
2. replace Serial.read() with Serial.parseInt():
int ledStatus = Serial.parseInt();
This will actually work with more general inputs, e.g. 123, but it will return 0 if there is anything different from a digit in the input buffer.
3. wrap Serial.read() within atoi():
byte ledStatus = atoi(Serial.read());
This is somewhat more limited than both of previous options, since now you can only have 10 cases in your switch.
So for an assignment I have for my Computer Systems class, I need to type characters in the command line when the program runs.
These characters (such as abcd ef) would be stored in argv[].
The parent sends these characters one at a time through a pipe to the child process which then counts the characters and ignores spaces. After all the characters are sent, the child then returns the number of characters that it counted for the parent to report.
When I try to run the program as it is right now, it tells me the value of readIn is 4, the child processed 0 characters and charCounter is 2.
I feel like I'm so close but I'm missing something important :/ The char array for a and in the parent process was an attempt to hardcode the stuff in to see if it worked but I am still unsuccessful. Any help would be greatly appreciated, thank you!
// Characters from command line arguments are sent to child process
// from parent process one at a time through pipe.
//
// Child process counts number of characters sent through pipe.
//
// Child process returns number of characters counted to parent process.
//
// Parent process prints number of characters counted by child process.
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h> // for fork()
#include <sys/types.h> // for pid_t
#include <sys/wait.h> // for waitpid()
int main(int argc, char **argv)
{
int fd[2];
pid_t pid;
int status;
int charCounter = 0;
int nChar = 0;
char readbuffer[80];
char readIn = 'a';
//char a[] = {'a', 'b', 'c', 'd'};
pipe(fd);
pid = fork();
if (pid < 0) {
printf("fork error %d\n", pid);
return -1;
}
else if (pid == 0) {
// code that runs in the child process
close(fd[1]);
while(readIn != 0)
{
readIn = read(fd[0], readbuffer, sizeof(readbuffer));
printf("The value of readIn is %d\n", readIn);
if(readIn != ' ')
{
charCounter++;
}
}
close(fd[0]);
//open(fd[1]);
//write(fd[1], charCounter, sizeof(charCounter));
printf("The value of charCounter is %d\n", charCounter);
return charCounter;
}
else
{
// code that runs in the parent process
close(fd[0]);
write(fd[1], &argv, sizeof(argv));
//write(fd[1], &a, sizeof(a));
close(fd[1]);
//open(fd[0]);
//nChar = read(fd[0], readbuffer, sizeof(readbuffer));
nChar = charCounter;
printf("CS201 - Assignment 3 - Andy Grill\n");
printf("The child processed %d characters\n\n", nChar);
if (waitpid(pid, &status, 0) > 0)
{
if (WIFEXITED(status))
{
}
else if (WIFSIGNALED(status))
{
}
}
return 0;
}
}
You're misusing pipes.
A pipe is a unidirectional communication channel. Either you use it to send data from a parent process to a child process, or to send data from a child process to the parent. You can't do both - even if you kept the pipe's read and write channels open on both processes, each process would never know when it was its turn to read from the pipe (e.g. you could end up reading something in the child that was supposed to be read by the parent).
The code to send the characters from parent to child seems mostly correct (more details below), but you need to redesign child to parent communication. Now, you have two options to send the results from child to parent:
Use another pipe. You set up an additional pipe before forking for child-to-parent communication. This complicates the design and the code, because now you have 4 file descriptors to manage from 2 different pipes, and you need to be careful where you close each file descriptor to make sure processes don't hang. It is also probably a bit overkill because the child is only sending a number to the parent.
Return the result from the child as the exit value. This is what you're doing right now, and it's a good choice. However, you fail to retrieve that information in the parent: the child's termination status tells you the number of characters processed, you can fetch this value with waitpid(2), which you already do, but then you never look at status (which contains the results you're looking for).
Remember that a child process has its own address space. It makes no sense to try to read charCounter in the parent because the parent never modified it. The child process gets its own copy of charCounter, so any modifications are seen by the child only. Your code seems to assume otherwise.
To make this more obvious, I would suggest moving the declarations of variables to the corresponding process code. Only fd and pid need to be copied in both processes, the other variables are specific to the task of each process. So you can move the declarations of status and nChar to the parent process specific code, and you can move charCounter, readbuffer and readIn to the child. This will make it very obvious that the variables are completely independent on each process.
Now, some more specific remarks:
pipe(2) can return an error. You ignore the return value, and you shouldn't. At the very least, you should print an error message and terminate if pipe(2) failed for some reason. I also noticed you report errors in fork(2) with printf("fork error %d\n", pid);. This is not the correct way to do it: fork(2) and other syscalls (and library calls) always return -1 on error and set the errno global variable to indicate the cause. So that printf() will always print fork error -1 no matter what the error cause was. It's not helpful. Also, it prints the error message to stdout, and for a number of reasons, error messages should be printed to stderr instead. So I suggest using perror(3) instead, or manually print the error to stderr with fprintf(3). perror(3) has the added benefit of appending the error message description to the text you feed it, so it's usually a good choice.
Example:
if (pipe(fd) < 0) {
perror("pipe(2) error");
exit(EXIT_FAILURE);
}
Other functions that you use throughout the code may also fail, and again, you are ignoring the (possible) error returns. close(2) can fail, as well as read(2). Handle the errors, they are there for a reason.
The way you use readIn is wrong. readIn is the result of read(2), which returns the number of characters read (and it should be an int). The code uses readIn as if it were the next character read. The characters read are stored in readbuffer, and readIn will tell you how many characters are on that buffer. So you use readIn to loop through the buffer contents and count the characters. Something like this:
readIn = read(fd[0], readbuffer, sizeof(readbuffer));
while (readIn > 0) {
int i;
for (i = 0; i < readIn; i++) {
if (readbuffer[i] != ' ') {
charCounter++;
}
}
readIn = read(fd[0], readbuffer, sizeof(readbuffer));
}
Now, about the parent process:
You are not writing the characters into the pipe. This is meaningless:
write(fd[1], &argv, sizeof(argv));
&argv is of type char ***, and sizeof(argv) is the same as sizeof(char **), because argv is a char **. Array dimensions are not kept when passed into a function.
You need to manually loop through argv and write each entry into the pipe, like so:
int i;
for (i = 1; i < argv; i++) {
size_t to_write = strlen(argv[i]);
ssize_t written = write(fd[1], argv[i], to_write);
if (written != to_write) {
if (written < 0)
perror("write(2) error");
else
fprintf(stderr, "Short write detected on argv[%d]: %zd/zd\n", i, written, to_write);
}
}
Note that argv[0] is the name of the program, that's why i starts at 1. If you want to count argv[0] too, just change it to start at 0.
Finally, as I said before, you need to use the termination status fetched by waitpid(2) to get the actual count returned by the child. So you can only print the result after waitpid(2) returned and after making sure the child terminated gracefully. Also, to fetch the actual exit code you need to use the WEXITSTATUS macro (which is only safe to use if WIFEXITED returns true).
So here's the full program with all of these issues addressed:
// Characters from command line arguments are sent to child process
// from parent process one at a time through pipe.
//
// Child process counts number of characters sent through pipe.
//
// Child process returns number of characters counted to parent process.
//
// Parent process prints number of characters counted by child process.
#include <stdlib.h>
#include <stdio.h>
#include <string.h> // for strlen()
#include <unistd.h> // for fork()
#include <sys/types.h> // for pid_t
#include <sys/wait.h> // for waitpid()
int main(int argc, char **argv)
{
int fd[2];
pid_t pid;
if (pipe(fd) < 0) {
perror("pipe(2) error");
exit(EXIT_FAILURE);
}
pid = fork();
if (pid < 0) {
perror("fork(2) error");
exit(EXIT_FAILURE);
}
if (pid == 0) {
int readIn;
int charCounter = 0;
char readbuffer[80];
if (close(fd[1]) < 0) {
perror("close(2) failed on pipe's write channel");
/* We use abort() here so that the child terminates with SIGABRT
* and the parent knows that the exit code is not meaningful
*/
abort();
}
readIn = read(fd[0], readbuffer, sizeof(readbuffer));
while (readIn > 0) {
int i;
for (i = 0; i < readIn; i++) {
if (readbuffer[i] != ' ') {
charCounter++;
}
}
readIn = read(fd[0], readbuffer, sizeof(readbuffer));
}
if (readIn < 0) {
perror("read(2) error");
}
printf("The value of charCounter is %d\n", charCounter);
return charCounter;
} else {
int status;
if (close(fd[0]) < 0) {
perror("close(2) failed on pipe's read channel");
exit(EXIT_FAILURE);
}
int i;
for (i = 1; i < argc; i++) {
size_t to_write = strlen(argv[i]);
ssize_t written = write(fd[1], argv[i], to_write);
if (written != to_write) {
if (written < 0) {
perror("write(2) error");
} else {
fprintf(stderr, "Short write detected on argv[%d]: %zd/%zd\n", i, written, to_write);
}
}
}
if (close(fd[1]) < 0) {
perror("close(2) failed on pipe's write channel on parent");
exit(EXIT_FAILURE);
}
if (waitpid(pid, &status, 0) < 0) {
perror("waitpid(2) error");
exit(EXIT_FAILURE);
}
if (WIFEXITED(status)) {
printf("CS201 - Assignment 3 - Andy Grill\n");
printf("The child processed %d characters\n\n", WEXITSTATUS(status));
} else if (WIFSIGNALED(status)) {
fprintf(stderr, "Child terminated abnormally with signal %d\n", WTERMSIG(status));
} else {
fprintf(stderr, "Unknown child termination status\n");
}
return 0;
}
}
Some final notes:
The shell splits arguments by spaces, so if you start the program as ./a.out this is a test, the code will not see a single space. This is irrelevant, because spaces are supposed to be ignored anyway, but if you want to test that the code really ignores spaces, you need to quote the parameters so that the shell does not process them, as in ./a.out "this is a test" "hello world" "lalala".
Only the rightmost (least significant) 8 bits of a program's exit code are used, so WEXITSTATUS will never return more than 255. If the child reads more than 255 characters, the value will wrap around, so you effectively have a character counter modulo 256. If this is a problem, then you need to go with the other approach and set up a 2nd pipe for child-to-parent communication and write the result there (and have the parent read it). You can confirm this on man 2 waitpid:
WEXITSTATUS(status)
returns the exit status of the child. This consists of the least
significant 8 bits of the status argument that the child
specified in a call to exit(3) or _exit(2) or as the argument for a return
statement in main(). This macro should be employed only if
WIFEXITED returned true.
I'm parsing a very large CSV file using GCD functions (please see code below).
If I encounter an error I'd like to cancel dispatch_io_read. Is there a way to do that?
dispatch_io_read(channel,
0,
Int.max,
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0))
{ (done, data, error) in
guard error == 0 else {
print("Read Error: \(error)")
return
}
if done {
lineBuffer.dealloc(bufferSize)
}
dispatch_data_apply(data)
{ (region, offset, buffer, size) -> Bool in
print(size)
let bytes = UnsafePointer<UInt8>(buffer)
for var i = 0; i < size; i++ {
switch bytes[i] {
case self.cr: // ignore \r
break
case self.lf: // newline
lineBuffer[bufferLength] = 0x00 // Null terminated
line(line: String(UTF8String: lineBuffer)!)
bufferLength = 0
case _ where bufferLength < (bufferSize - 1): // Leave space for null termination
lineBuffer[bufferLength++] = CChar(bytes[i])
default:
return false // Overflow! I would like to stop reading the file here.
}
}
return true
}
}
Calling dispatch_io_close(DISPATCH_IO_STOP) will cause running dispatch_io_read operations to be interrupted and their handlers to be passed to ECANCELED error (along with partial results), see the dispatch_io_close(3) manpage.
Note that this does not interrupt the actual I/O system calls, it just prevents additional I/O system calls from being entered, so you may have to set an I/O channel high watermark to ensure the appropriate level of I/O granularity for your application.
I am currently working at a logger that uses a MSP430F2618 MCU and SanDisk 4GB SDHC Card.
Card initialization works as expected, I also can read MBR and FAT table.
The problem is that I can't write any data on it. I have checked if it is write protected by notch, but it's not. Windows 7 OS has no problem reading/writing to it.
Though, I have used a tool called "HxD" and I've tried to alter some sectors (under Windows). When I try to save the content to SD card, the tool pop up a windows telling me "Access denied!".
Then I came back to my code for writing to SD card:
uint8_t SdWriteBlock(uchar_t *blockData, const uint32_t address)
{
uint8_t result = OP_ERROR;
uint16_t count;
uchar_t dataResp;
uint8_t idx;
for (idx = RWTIMEOUT; idx > 0; idx--)
{
CS_LOW();
SdCommand(CMD24, address, 0xFF);
dataResp = SdResponse();
if (dataResp == 0x00)
{
break;
}
else
{
CS_HIGH();
SdWrite(0xFF);
}
}
if (0x00 == dataResp)
{
//send command success, now send data starting with DATA TOKEN = 0xFE
SdWrite(0xFE);
//send 512 bytes of data
for (count = 0; count < 512; count++)
{
SdWrite(*blockData++);
}
//now send tow CRC bytes ,through it is not used in the spi mode
//but it is still needed in transfer format
SdWrite(0xFF);
SdWrite(0xFF);
//now read in the DATA RESPONSE TOKEN
do
{
SdWrite(0xFF);
dataResp = SdRead();
}
while (dataResp == 0x00);
//following the DATA RESPONSE TOKEN are a number of BUSY bytes
//a zero byte indicates the SD/MMC is busy programing,
//a non_zero byte indicates SD/MMC is not busy
dataResp = dataResp & 0x0F;
if (0x05 == dataResp)
{
idx = RWTIMEOUT;
do
{
SdWrite(0xFF);
dataResp = SdRead();
if (0x0 == dataResp)
{
result = OP_OK;
break;
}
idx--;
}
while (idx != 0);
CS_HIGH();
SdWrite(0xFF);
}
else
{
CS_HIGH();
SdWrite(0xFF);
}
}
return result;
}
The problem seems to be when I am waiting for card status:
do
{
SdWrite(0xFF);
dataResp = SdRead();
}
while (dataResp == 0x00);
Here I am waiting for a response of type "X5"(hex value) where X is undefined.
But most of the cases the response is 0x00 (hex value) and I don't get out of the loop. Few cases are when the response is 0xFF (hex value).
I can't figure out what is the problem.
Can anyone help me? Thanks!
4GB SDHC
We need to see much more of your code. Many µC SPI codebases only support SD cards <= 2 GB, so using a smaller card might work.
You might check it yourself: SDHC needs a CMD 8 and an ACMD 41 after the CMD 0 (GO_IDLE_STATE) command, otherwise you cannot read or write data to it.
Thank you for your answers, but I solved my problem. It was a problem of timing. I had to put a delay at specific points.