Hi,
I am having problems with lost serial interrupts. Could you please
explain to me why this happens ? I am probably missing something
regarding scheduling in Xenomai...
I prepared a program that triggers the problem, at least on my system.
Thanks,
Tomas
The program works on my system as follows:
1. I run the program, it prints
In interrupt, LStatus: 96
In interrupt, read char, LStatus: 96
[which means that it received a serial interrupt, because the
transmitter receiver is empty]
2. I send a single character to the program over serial line
3. the program wakes up (10 seconds after (1))
4. the program prints
I-NFO irq=4 hits=1
PIC-ISR:0 PIC-IRR:0 PIC-IMR:128 UART-IIR:4 UART-LSR:97 UART-MSR:176
[which means the interrupt at Xenomai level hit only once, although it
should have twice, second time because of the received character
these too lines that repeat indefinitely, the interrupt not coming.
although interrupts are enabled at PIC level]
I use the "XT-PIC-XT" (8259A) interrupt controller. As far as I know,
Linux sets up the controller to "edge triggering", but uses
"handle_level_irq" for it. When received by Xenomai, the interrupt is
masked and acked at PIC level ( "ack" means EOI at 8259A). When the
interrupt handling in the program finishes, it unmasks the interrupt. I
verified that my 8259A has a latch that can detect the UART interrupt
even if masked, so that when unmasked again, it can be delivered.
#include <stdio.h>
#include <sys/io.h>
#include <unistd.h>
#include <native/task.h>
#include <native/intr.h>
#include <sys/mman.h>
#define BASEPORT 0x3f8
#define IRQ_NUMBER 0x4
RT_INTR intr_desc;
RT_TASK sender_desc, task_main;
inline void nfo() {
int isr, irr, imr;
int iir, lsr, msr;
outb(0x0b, 0x20);
isr = inb(0x20);
outb(0x0a, 0x20);
irr = inb(0x20);
imr = inb(0x21);
iir = inb(BASEPORT +2);
lsr = inb(BASEPORT +5);
msr = inb(BASEPORT +6);
fprintf(stderr, "PIC-ISR:%d PIC-IRR:%d PIC-IMR:%d UART-IIR:%d UART-LSR:%d
UART-MSR:%d\n",
isr, irr, imr, iir, lsr, msr);
}
void sender_task (void *cookie) {
int res;
for(;;) {
res = rt_intr_wait(&intr_desc, TM_INFINITE);
if (res<=0) {
perror("rt_intr_wait: ");
continue;
}
fprintf(stderr,"In interrupt, LStatus: %d \n", inb(BASEPORT +5));
inb(BASEPORT);
fprintf(stderr,"In interrupt, read char, LStatus: %d \n",
inb(BASEPORT +5));
rt_intr_enable( &intr_desc );
}
}
RT_INTR_INFO intr_nfo;
int main(int argc, char **argv) {
int res,i;
if (iopl(3)) {
perror("iopl:");
return 1;
}
mlockall(MCL_CURRENT|MCL_FUTURE);
res = rt_intr_create(&intr_desc, NULL, IRQ_NUMBER, I_NOAUTOENA);
// res = rt_intr_create(&intr_desc, NULL, IRQ_NUMBER, 0);
if (res) {
perror("rt_intr_create:");
return 1;
}
res = rt_task_create(&sender_desc, NULL, 0, 99, 0);
if (res) {
perror("rt_task_create:");
return 1;
}
rt_task_start(&sender_desc, &sender_task, NULL);
outb( 0x00, BASEPORT + 1);
outb( 0x80, BASEPORT + 3 );
outb( 0x01, BASEPORT + 0 );
outb( 0x00, BASEPORT + 1 );
outb( 0x03, BASEPORT + 3 );
// FIFO on, interrupt after one byte
outb( 0x7, BASEPORT + 2);
// FIFO off
outb( 0x0, BASEPORT + 2);
outb( 0xb, BASEPORT + 4 ); // force rts on
// outb( 0x9, BASEPORT + 4 ); // do not force rts
rt_intr_enable( &intr_desc );
outb( 15, BASEPORT + 1 );
rt_task_shadow( &task_main, NULL, 1, 0);
while (1) {
rt_task_sleep(10000000000ULL);
rt_intr_inquire(&intr_desc, &intr_nfo);
fprintf(stderr,"I-NFO irq=%d hits=%d\n", intr_nfo.irq, intr_nfo.hits);
nfo();
}
fprintf(stderr,"Main: no more characters to send...\n");
}
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