It's possible to sample the value on hostmot2 physical I/O pins even
when they are used as outputs--either gpio or special-purpose modules
like stepgen.
Use 1 (most useful): For an open-drain output, the pin can be driven
low by an external source. This allows a sort of one-wire handshake.
Use 2: You can read the output of a special purpose module.
Reading the output of a special-purpose module probably has limited
usefulness--since it samples at a very low rate, you can't see the true
step+direction waveform, just like sampling a software stepgen's step
pin in the servo-thread of a system where it runs on the base-thread
gives misleading results.
But it might be useful in a few special circumstances; for instance, by
properly setting the step timings it might be possible to guarantee
catching every output transition, and this could be used in some kind of
testing.
Use 3 (least useful): For the sake of consistency, a gpio "in" pin now
tracks the corresponding "out" pin, for push-pull outputs.
Jeff
Index: ioport.c
===================================================================
RCS file: /cvs/emc2/src/hal/drivers/mesa-hostmot2/ioport.c,v
retrieving revision 1.11
diff -u -p -r1.11 ioport.c
--- ioport.c 21 Feb 2009 01:53:07 -0000 1.11
+++ ioport.c 4 Jun 2009 22:11:18 -0000
@@ -217,40 +217,35 @@ int hm2_ioport_gpio_export_hal(hostmot2_
//
- // it's a full GPIO or it's an input for some other module
+ // all pins' values can be read; for pins used as outputs
+ // (including special-purpose outputs), the output value is sampled.
//
- if (
- (hm2->pin[i].gtag == HM2_GTAG_IOPORT)
- || (hm2->pin[i].direction == HM2_PIN_DIR_IS_INPUT)
- ) {
-
- // pins
- r = hal_pin_bit_newf(
- HAL_OUT,
- &(hm2->pin[i].instance->hal.pin.in),
- hm2->llio->comp_id,
- "%s.gpio.%03d.in",
- hm2->llio->name,
- i
- );
- if (r != HAL_SUCCESS) {
- HM2_ERR("error %d adding gpio pin, aborting\n", r);
- return -EINVAL;
- }
-
- r = hal_pin_bit_newf(
- HAL_OUT,
- &(hm2->pin[i].instance->hal.pin.in_not),
- hm2->llio->comp_id,
- "%s.gpio.%03d.in_not",
- hm2->llio->name,
- i
- );
- if (r != HAL_SUCCESS) {
- HM2_ERR("error %d adding gpio pin, aborting\n", r);
- return -EINVAL;
- }
+ // pins
+ r = hal_pin_bit_newf(
+ HAL_OUT,
+ &(hm2->pin[i].instance->hal.pin.in),
+ hm2->llio->comp_id,
+ "%s.gpio.%03d.in",
+ hm2->llio->name,
+ i
+ );
+ if (r != HAL_SUCCESS) {
+ HM2_ERR("error %d adding gpio pin, aborting\n", r);
+ return -EINVAL;
+ }
+
+ r = hal_pin_bit_newf(
+ HAL_OUT,
+ &(hm2->pin[i].instance->hal.pin.in_not),
+ hm2->llio->comp_id,
+ "%s.gpio.%03d.in_not",
+ hm2->llio->name,
+ i
+ );
+ if (r != HAL_SUCCESS) {
+ HM2_ERR("error %d adding gpio pin, aborting\n", r);
+ return -EINVAL;
}
@@ -502,8 +497,6 @@ void hm2_ioport_gpio_process_tram_read(h
int io_pin = (port * hm2->idrom.port_width) + port_pin;
hal_bit_t bit;
- if (hm2->pin[io_pin].direction != HM2_PIN_DIR_IS_INPUT) continue;
-
bit = (hm2->ioport.data_read_reg[port] >> port_pin) & 0x1;
*hm2->pin[io_pin].instance->hal.pin.in = bit;
*hm2->pin[io_pin].instance->hal.pin.in_not = !bit;
------------------------------------------------------------------------------
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