I'm working on uploading to Digispark board. It uses micronucleus bootloader and i can see uploader code. I've modified it a bit to see interfaces and endpoints count:
nucleus->device = usb_open(dev);
// added by me - start
int interfaces, endpoints, j;
struct usb_interface_descriptor *interface = NULL;
interfaces = dev->config->bNumInterfaces;
fprintf(stderr, "Found interfaces: %i\n", interfaces);
interface = &(dev->config->interface[0].altsetting[0]);
fprintf(stderr, "Endpoints: %i\n", interface->bNumEndpoints);
// added by me - end
// get nucleus info
unsigned char buffer[4];
int res = usb_control_msg(nucleus->device, USB_ENDPOINT_IN| USB_TYPE_VENDOR | USB_RECIP_DEVICE, 0, 0, 0, (char *)buffer, 4, MICRONUCLEUS_USB_TIMEOUT);
I wonder how it's working because interface #0 has no endpoints:
$./micronucleus --type intel-hex /tmp/Start.ino.hex
> Please plug in the device ...
> Press CTRL+C to terminate the program.
Found interfaces: 1
Endpoints: 0
> Device is found!
connecting: 40% complete
> Device has firmware version 1.6
> Available space for user applications: 6012 bytes
> Suggested sleep time between sending pages: 8ms
> Whole page count: 94 page size: 64
> Erase function sleep duration: 752ms
parsing: 60% complete
> Erasing the memory ...
erasing: 80% complete
> Starting to upload ...
writing: 100% complete
>> Micronucleus done. Thank you!
Usually i expect interface to have 2 endpoints (in & out from usb.h):
#define USB_ENDPOINT_IN 0x80
#define USB_ENDPOINT_OUT 0x00
Can anyone explain me how usb_control_msg(nucleus->device, USB_ENDPOINT_IN| USB_TYPE_VENDOR | USB_RECIP_DEVICE, 0, 0, 0, (char *)buffer, 4, MICRONUCLEUS_USB_TIMEOUT); is working without endpoint?
Answered here: https://arduino.stackexchange.com/a/44026/8327. In brief: it does not have endpoints (except 0) and interacts using control transfers only.