CODEWITHSUNDEEP
c++cqtpiclibusb
rxmxn
rxmxn

Reputation: 499

Why do I get an error when read or write more than 3 bytes using libusb to communicate with a PIC 18F2550?

I'm using libusb in Qt to communicate with a PIC microcontroller, 18F2550. The thing is that it's working OK until I try to send or read more than three bytes. Why does it happen?

I've tried using bulk_read transfer and interrupt_read. When I put the size of the buffer equal or less than three, then the transmission works perfectly, using bulk or interrupt. When this size is greater than three, then I'm getting buffer1 and buffer[2] OK, but the rest are wrong.

The error that I'm getting is from timeout. As input I'm using endpoint 0x81.

More information:

The return value from the bulk or interrupt read is -116. The numbers that I'm sending from the PIC to the PC in the two first bytes ([0] and 1) in hex is 0x02D6. With this number, buffer[0] = -42 (when it should be 0xD6 = 214) and buffer[1] = 2 that is correct. In the [2] and [3] bytes the number is 0x033D, and I get [2] = 61 = 0x3D. That is correct and [3] = -42??? (like [0]).

And the fifth byte is 1, and the SW shows 2???. Might it be a problem in the microcontroller, because I'm programming it as an HID USB?

Upvotes: 1

Views: 468

Answers (1)

rgcalsaverini
rgcalsaverini

Reputation: 675

I don't think that being a HID is the problem. I had a similar issue before; the PIC would randomly timeout when large data was being transmitted. It turned out to be some voltage fluctuation on the MCU. How are you connecting the crystal? Do you have a capacitor on VUSB to regulate it?

Building a PIC18F USB device is a great tutorial on building a PIC HID, and even though it's not based on 18F2550 but on 18F4550, it should be quite similar, and I'm sure you can get a lot out of the schematics and hardware setup. It was the starting point for my PIC-USB projects.

Upvotes: 1

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