On May 14, 2009, at 6:56 PM, Martin Peach wrote:
Hans-Christoph Steiner wrote:
On May 9, 2009, at 2:43 PM, Martin Peach wrote:
Roman Haefeli wrote:
thanks for the info. On Fri, 2009-05-08 at 19:27 +0000, martin.peach@sympatico.ca wrote:
just out of curiosity: if there is a solution, that works well
for [tcpserver], couldn't it be applied also to [comport]?Maybe. But I think you should be able to use [comport] with no hardware handshaking enabled and send data even if no cable is attached. Sometimes the absence of one of the two input handshake signals prevents the serial hardware from sending. Also if an
error occurred in the reception of serial data it may not be handled properly in [comport]. So I'm not sure what is causing this
particular crash, since HC said that it happened when the remote device was disconnected but gave no further detail.iirc, on linux at least, [comport] makes pd hang, _whenever_ the
other end disappears. i.e.:
- pulling out the usb-cable, while the arduino is connected
- turning off an rfcomm device
This looks like something related to the usb interface. I think
pulling out an RS-232 cable has no effect, as the serial driver
can only be closed by [comport]. With a usb adapter the usb driver
can close the port. I suspect that the comport_tick routine, which is called
periodically to check for received characters, tries to access the
serial port after the usb driver has closed it. The non-Windows code in comport_tick looks like this:unsigned char serial_byte; fd_set com_rfds; int count = 0;
FD_ZERO(&com_rfds); FD_SET(fd,&com_rfds);
while((err=select(fd+1,&com_rfds,NULL,NULL,&null_tv)) > 0) { err = read(fd,(char *) &serial_byte,1); outlet_float(x->x_data_outlet, (t_float) serial_byte); ++count; }
As you can see the select call only checks for the presence of
received characters with com_rfds, and doesn't check the write or
exception status. I suppose the select call should also check the
exception fd_set, as the usb driver has no other way of informing
[comport] that it has closed the port, it should have flagged it
there. (Although if the fd itself is no longer valid I don't know what to
do...using non-existent file descriptors is a good way to crash Pd)ATM I only have 'legacy' RS-232 ports on my hardware so I can't
test it, but I can change the code.Martin
Ok, quick test shows a couple things:
- just using [comport 1 115200] and then yanking the USB out causes
the crash, so no data needs to be sent to cause this. This is with
a standard Arduino USB.So the crash most likely occurs when comport_tick is called by the
timer.
- in the select() that you highlight, it is just testing before
reading, so I am guessing it would not be so useful to do a write
test if it is only going to read().The write test is not needed, but I was thinking that the third
possible test, the exception test, might give useful info, unless
the file descriptor has already become invalid, in which case I
don't know what to do about it, since using a dead file descriptor
is usually lethal and probably is what is causing the crash. How does [hid] react to unplugging of the device?
In [hid] I don't remember doing anything special, I never even used
select(). I am guessing that serial ports behave differently that USB
HID. Serial was designed to be permanently attached, USB was designed
to be hot-pluggable. Here's the read() for example:
while( read (x->x_fd, &(hid_input_event), sizeof(struct
input_event)) > -1 )
I open it using read-only and non-blocking, maybe that has something
to do with it?
x->x_fd = open(block_device, O_RDONLY | O_NONBLOCK);
I just tried a test with just a USB serial adapter, it didn't actually
crash, it just stopped responding and pegged the CPU.
.hc
There is no way to peace, peace is the way. -A.J. Muste