P2 USB Serial is very slow compared to Photon

Firmware Device OS
21

I'm seeing similar results on 6.3.2.

1 Like
22

Not very familiar with how the underlying Device OS operates, but when it sends a packet to the Realtek PCD, that's blocking isn't it?

int RtlUsbDriver::transferIn(unsigned ep, const uint8_t* ptr, size_t size) {
    SPARK_ASSERT(rtlDev_);
    auto self = instance();
    std::lock_guard<RtlUsbDriver> lk(*self);
    if (ptr == nullptr && size == 0) {
        // FIXME
        void* pcd = *((void**)((uint8_t*)rtlDev_ + RTL_USB_DEV_PCD_OFFSET));
        usb_spinlock_t* lock = *((usb_spinlock_t**)((uint8_t*)pcd + RTL_USB_PCD_SPINLOCK_OFFSET));
        usb_os_spinlock(lock);
        auto r = usb_hal_write_packet(nullptr, ep & 0x7f, 0);
        usb_os_spinunlock(lock);
        return CHECK_RTL_USB_TO_SYSTEM(r);
    }
    return CHECK_RTL_USB_TO_SYSTEM(usbd_ep_transmit(rtlDev_, ep | SetupRequest::DIRECTION_DEVICE_TO_HOST, (uint8_t*)ptr, size));
}

If usbd_ep_transmit() is synchronous, we'd be waiting there until it takes our data even though we're no longer adding extra 1 ms delays in the HAL in 6.3.2.