Hello R.,
On 2013-08-01 12:51, R. Diez wrote:
Hallo all:
File cpukit/libcsupport/include/rtems/termiostypes.h defines the following
constants:
/*
* FIXME: this should move to libio.h!
* values for rtems_termios_callbacks.outputUsesInterrupts
*/
#define TERMIOS_POLLED 0
#define TERMIOS_IRQ_DRIVEN 1
#define TERMIOS_TASK_DRIVEN 2
However, some modules initialise rtems_termios_callbacks structures with fixed
values like this:
.outputUsesInterrupts = 1,
Others use one of the constants above.
I noticed because some drivers initialise a similar field in structure
console_fns with true/false, while others use the same constants as above.
Routine console_open() in c/src/lib/libbsp/shared/console.c copies this flag as
follows:
Callbacks.outputUsesInterrupts =
cptr->pDeviceFns->deviceOutputUsesInterrupts;
yes, this is bad. The console driver framework has a lot of stuff like this.
The problem is that from a functional point of view it works well and it seems
nobody has a budget to fix these more cosmetic issues.
That is copying information from structure console_fns to structure
rtems_termios_callbacks, but cptr->pDeviceFns->deviceOutputUsesInterrupts is of
type bool, whereas Callbacks.outputUsesInterrupts is an int.
What does TERMIOS_TASK_DRIVEN mean anyway? I didn't manage to find any
documentation about it.
If you look at a typical interrupt service routine
static void pl050_interrupt(void *arg)
{
int minor = (int) arg;
const console_data *cd = &Console_Port_Data[minor];
volatile pl050 *regs = pl050_get_regs(minor);
uint32_t kmiir_rx = PL050_KMIIR_KMIRXINTR;
uint32_t kmiir_tx = (regs->kmicr & PL050_KMICR_KMITXINTREN) != 0 ?
PL050_KMIIR_KMITXINTR : 0;
uint32_t kmiir = regs->kmiir;
if ((kmiir & kmiir_rx) != 0) {
char c = (char) PL050_KMIDATA_KMIDATA_GET(regs->kmidata);
rtems_termios_enqueue_raw_characters(cd->termios_data, &c, 1);
}
if ((kmiir & kmiir_tx) != 0) {
rtems_termios_dequeue_characters(cd->termios_data, 1);
}
}
then you see that two Termios functions are called. The do a lot of stuff.
This processing overhead increases the thread dispatch and interrupt latency.
To overcome this issue the TERMIOS_TASK_DRIVEN was added. Here the interrupt
handler only signals a special purpose task which performs the input/output
processing.
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : [email protected]
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Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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