blocking read is not blocking

This commit is contained in:
tth 2018-12-20 11:57:23 +01:00
parent 8a34fed6af
commit bb10042aae
6 changed files with 115 additions and 26 deletions

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@ -12,6 +12,11 @@ Pour en savoir plus sur ce passionnant projet, il y a le canal IRC
`#tetalab` sur le réseau Freenode et/ou les rencontres du mercredi
soir au DD2, à Mixart-Myrys.
# WTF status
Le `read` bloquant ne bloque pas. Ça craint grave.

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@ -22,6 +22,12 @@ par le professeur Cispeo.
Un petit exemple ?
Oui, voilà. À ce jour (20 déc. 2018), on va dire que ça ne marche pas.
Il faut dire que les `serial devices` ont toujours étés un peu le
domaine de la magie noire. Mais quand même, coincer sur un `read` qui
ne bloque pas, c'est un peu ironique.

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@ -1,7 +1,9 @@
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/select.h>
#include <string.h>
#include <unistd.h> //Used for UART
#include <fcntl.h> //Used for UART
#include <termios.h> //Used for UART
@ -60,13 +62,15 @@ fprintf(stderr, "%s ( %s %d )\n", __func__, port, baudrate);
// shall not cause the terminal device to become the controlling terminal
// for the process.
uart0 = open(port, O_RDWR | O_NOCTTY);
if (uart0== -1)
uart0 = open(port, O_RDONLY | O_NOCTTY);
if (uart0 < 0)
{
perror("unable to open uart ");
return -1;
}
return uart0; /* WTF ??? */
// CONFIGURE THE UART
// The flags defined in /usr/include/termios.h -
// see http://pubs.opengroup.org/onlinepubs/007908799/xsh/termios.h.html
@ -87,6 +91,9 @@ baudbits = baudrate2const(baudrate);
#if DEBUG_LEVEL
fprintf(stderr, "%d -> 0x%04x\n", baudrate, baudbits);
#endif
memset(&options, 0, sizeof(options));
tcgetattr(uart0, &options);
options.c_cflag = baudbits | CS8 | CLOCAL | CREAD; //<Set baud rate
options.c_iflag = IGNPAR;
@ -100,16 +107,20 @@ return uart0;
/* -------------------------------------------------------------------- */
/*
* this function have NO timeout !
* blocking read is not blocking, wtf ?
*/
int getbyte(int fd)
{
unsigned char byte;
int foo;
byte = 0;
foo = read(fd, &byte, 1);
if (1 != foo)
{
perror("read a byte");
fprintf(stderr, "byte %d rd %d errno %d\n",
byte, foo, errno);
return -1;
}
return (int)byte;
@ -126,9 +137,8 @@ int retval;
timeout.tv_sec = to_ms / 1000;
timeout.tv_usec = (to_ms % 1000) * 1000;
#if DEBUG_LEVEL
fprintf(stderr, "timeout %6d is %4ld %6ld\n", to_ms,
fprintf(stderr, "timeout %6d is %4ld.%6ld\n", to_ms,
timeout.tv_sec, timeout.tv_usec);
#endif
@ -136,38 +146,37 @@ FD_ZERO (&rfds);
FD_SET (fd, &rfds);
retval = select(1, &rfds, NULL, NULL, &timeout);
#if DEBUG_LEVEL
fprintf(stderr, "%s : select -> %d\n", __func__, retval);
#endif
retval = retval < 0 ? -1 : retval;
switch (retval) {
case -1:
fprintf(stderr, "omg ?\n");
byte = -1;
retval = -1;
break;
case 0:
fprintf(stderr, "timeout\n");
byte = -99;
retval = -99;
break;
default:
fprintf(stderr, "%s default -> %d\n", __func__, retval);
if (retval==fd) {
read(fd, &byte, 1);
fprintf(stderr, "got 0x%02x\n", byte);
retval = byte;
}
else {
fprintf(stderr, "%d bad fd ?\n", retval);
byte = -3;
retval = -3;
}
break;
}
return byte;
return retval;
}
/* -------------------------------------------------------------------- */
/* timeout is in milliseconds */
@ -195,15 +204,21 @@ for(;;) {
retval = curpos;
}
if (curpos < szm) { /* ya de la place */
where[curpos] = byte;
curpos++;
}
else { /* oups overflow */
retval = -6;
break;
}
}
fprintf(stderr, "%s -> '%s'\n", __func__, where);
return -666;
return retval;
}
/* -------------------------------------------------------------------- */

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@ -6,7 +6,7 @@
int prepare_UART(char *port, int bauds);
int getbyte(int fd);
int getbyte(int fd); /* really brotched func */
/* timeout is exprimed in milliseconds. */

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@ -1,28 +1,36 @@
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "serial.h"
int verbosity;
int main (int argc, char *argv[])
{
int serial_in;
int byte, foo, to;
int byte;
serial_in = prepare_UART("/dev/ttyS0", 9600);
serial_in = prepare_UART("/dev/ttyACM0", 9600);
fprintf(stderr, "prepare uart -> %d\n", serial_in);
for (foo=0; foo<20; foo++) {
to = (foo+1) * 666;
byte = getbyte_to(serial_in, to);
if (serial_in < 0) {
exit(1);
}
for (;;) {
byte = getbyte(serial_in);
if (byte < 0) {
fprintf(stderr, "get byte : err is %d\n", byte);
}
// XXX else {
printf("%9ld %6d %6d %02x\n",
time(NULL), foo, to, byte);
// XXX }
else {
printf("%9ld %02x/%d\n",
time(NULL), byte, byte);
}
}
return 0;

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@ -0,0 +1,55 @@
/*
* simulateur de telemesure automate
*/
/* -------------------------------------------------- */
#define NBVAL 4
int values[NBVAL];
/* -------------------------------------------------- */
void setup() {
int foo;
Serial.begin(9600);
pinMode(LED_BUILTIN, OUTPUT);
for (foo=0; foo<NBVAL; foo++) {
values[foo] = 0;
}
}
/* -------------------------------------------------- */
void updatevalues(void)
{
int foo;
for (foo=0; foo<NBVAL; foo++) {
if (rand()%100<33) {
values[foo] += (foo + 1);
}
if (values[foo] > 1023) {
values[foo] = rand()%15;
}
}
}
/* -------------------------------------------------- */
void sendvalues(void)
{
int foo;
Serial.print("X ");
for (foo=0; foo<NBVAL; foo++) {
Serial.print(" ");
Serial.print(values[foo]);
}
Serial.print("\n");
}
/* -------------------------------------------------- */
void loop() {
updatevalues();
sendvalues();
delay(5000);
}
/* -------------------------------------------------- */