Hello All,
I'm looking for ideas on how to close and re-open devices on eCos. The
needs for this are (1) to support swappable/removable devices, (2) to
have a consistent way to put devices into a low-power state when they
are not being used, and (3) to prevent devices from using the CPU when
they are not needed.
On a current project for a battery-powered device, I have a need for all
of this: a CompactFlash that can be removed; a GPS that sends data
constantly, but only needs to be read once every few hours; and many of
the peripherals need to be put in a consistent state prior to going into
a low power mode.
I've been able to accomplish all of this with ugly application-level
code, but thought that a much better solution would be to propagate the
close() call of a devfs device down to the driver, so you could do this:
while (true) {
int fd = open("/dev/ser0", O_RDONLY);
read(fd, buf, BUF_LEN);
// power down the port
close(fd);
sleep(60);
}
I think this can be done pretty easily by adding a "shutdown" function
to the devtab entries:
typedef struct cyg_devtab_entry {
// ...
Cyg_ErrNo (*lookup)(struct cyg_devtab_entry **tab,
struct cyg_devtab_entry *sub_tab,
const char *name);
Cyg_ErrNo (*shutdown)(struct cyg_devtab_entry *tab);
// ...
} CYG_HAL_TABLE_TYPE cyg_devtab_entry_t;
The existing macros CHAR_DEVTAB_ENTRY, BLOCK_DEVTAB_ENTRY, etc, can just
insert an empty function into the shutdown slot, whereas a new set of
macros can accept the shutdown pointer:
#define
CHAR_CLOSABLE_DEVTAB_ENTRY(_l,_name,_dep_name,_handlers,_init,_lookup,_shutdown,_priv)
...
#define
BLOCK_CLOSABLE_DEVTAB_ENTRY(_l,_name,_dep_name,_handlers,_init,_lookup,_shutdown,_priv)
...
The assumption is that anything done in the shutdown would be undone in
a subsequent lookup so that the devices could bre closed then re-opened,
and that the shutdown would mark the entry as "unavailable":
tab->status &= ~CYG_DEVTAB_STATUS_AVAIL;
Assuming that this is a good way to handle this I would need to know how
to hook this into the upper-level device and file operations. What would
be needed?
Thanks,
Frank
