USB serial doesn't open immediately after reset

[andrewjherbert]

If my program commences output to the USBserial port immediately after reset the initial output is lost.

Putting a 1000ms delay at the start of my program cures the problem.

Another work-around is as follows:

#include "tusb.h"
int main() {
stdio_init_all();
adc_init();
printf("waiting for usb host");
while (!tud_cdc_connected()) {
printf(".");
sleep_ms(500);
}
printf("\nusb host detected!\n");

But this too appears to be time sensitive - if I make the sleep <= 10ms I still lose the first line.

It would be nice to have a helper function that gets this right, or an option on opening the port.

Thanks.

[lurch]

Related to #288 and raspberrypi/pico-examples#60

I know very little about the lowlevels of USB, but I think some of the timing-sensitive delay might be partly due to the USB enumeration-process happening on the host?

[andrewjherbert]

Good thought, and I guess this will arise every time the Pico restarts as the host will detect the disconnect / reconnect? The host is a RPi4 running Raspbian. I guess the solution is to use UART serial but that involves another set of cables and in my application I have mortgaged most of the GPIO pins to other purposes. Am I correct in understanding that I can connect to any one set of UART GPIO pins for this purpose, I don’t have to use the first set as per the examples, or do I have to do something to point the Pico at the right set? Cheers, Andrew (aka EDSAC)

…

On 11 Apr 2021, at 23:43, Andrew Scheller ***@***.***> wrote: Related to #288 <https://github.com/raspberrypi/pico-sdk/issues/288> and raspberrypi/pico-examples#60 <raspberrypi/pico-examples#60> I know very little about the lowlevels of USB, but I think some of the timing-sensitive delay might be partly due to the USB enumeration-process happening on the host? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#333 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AOZH36OWCUUMZXYXN66CIYTTIIQ2VANCNFSM42YEREMQ>.

[lurch]

Am I correct in understanding that I can connect to any one set of UART GPIO pins for this purpose, I don’t have to use the first set as per the examples, or do I have to do something to point the Pico at the right set?

There's some handy defines in https://github.com/raspberrypi/pico-sdk/blob/master/src/boards/include/boards/pico.h 😃
To override their values, just define them in your own application code before including any pico-sdk headers.

[andrewjherbert]

Great, thanks! A.

…

On 12 Apr 2021, at 10:36, Andrew Scheller ***@***.***> wrote: Am I correct in understanding that I can connect to any one set of UART GPIO pins for this purpose, I don’t have to use the first set as per the examples, or do I have to do something to point the Pico at the right set? There's some handy defines in https://github.com/raspberrypi/pico-sdk/blob/master/src/boards/include/boards/pico.h <https://github.com/raspberrypi/pico-sdk/blob/master/src/boards/include/boards/pico.h> 😃 To override their values, just define them in your own application code before including any pico-sdk headers. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#333 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AOZH36LLWYUPC4IKSYL4AB3TIK5IBANCNFSM42YEREMQ>.

[lurch]

From one Andrew to another, you're welcome! 😁

[kilograham]

having a "wait for connected" method should be a separate issue (there may be one)