How to get maximum USB throughput

How to get maximum USB throughput using PIC32 as USB device?

I need to send data from PIC32 to PC as fast as possible - at least about 1 megabyte per second.
Have anybody tried that?
How should I configure USB in PIC32?
Can I use one of predefined USB device classes?
I used to use RS emulation (CDC), but it's definitelly too slow for this application (up to 64kB per second if I'm not mistaken).

Thanks. I will look into that. I don't need constant datarate. I just have about 4GB to send and this shouldn't take much more than 1 hour.

I have made a set of tests (bulk transfer) and I'm only able to get about 630kB/s (PIC to PC) datarate. Are there any special tricks I need to implement to get closer to 1MB/s?

I am basing my firmware on Libusb demo from Microchip stack. I have added a new "function" in the firmware (case 0x40) that sends a set of (16384) packets - 64 bytes each. Host reads those and measures times using Windows' PerformanceCounter.

The strange thing I have found is that speed is different if I plug the device into another USB port (in fact using a hub looks faster... really strange). Another thing is that compiling the code with optimisation on returns 630kB/s while using optimisised compilation I only get 520kB/s. So... I'm not sure where is the bottleneck (bus or PIC)

My ideas to optimise:
1) learn about PIC32 usb module - will it allow in/out buffers larger than one block? (per endpoint)
2) use two endpoints per transfer - this way I will be able to setup one packet while previous one was being send
3) move sending loop into USB ISR so I will get rid if "while" waiting loop in main code (main code will need to manage incoming transfer using PMP - already fully working with DMA)
4) try other computer that doesn't have any USB devices attached

Any hints welcome

My test PC program was looping to read in 256kB chunks. That was guided by my final application's requirements (it will request data in such sized chunks). I have changed it to 1MB for testing and there was no difference in speed.

I have tested with another PC (notebook) and results are almost ideally the same (both with optimised PIC code - 630kB/s; and unoptimised one - 530kB/s).


I'm starting to think something in the PIC makes the code run too slow. Maybe interrupts are issued to late (USB is working on interrupts) or something like that....


New test (faster!). I've moved USB ISR to IPL7 so it uses secondary register set. Result: speed with optimised code is now 689kB/s.


Now I think the trick to make it faster would be changing USB ISR in a way that is optimised in servicing bulk IN transfers, maybe even bulk IN transfer on this one given endpoint.

(BTW: yes, I know using USB in pooling mode should be faster if PIC was doing nothing more than USB; but it will not be a real world scenerio)

Could you tell me :  How you testing speed between PC and PIC32 ? 

COuld you tell me How you configured Che ?? I use this demo too .

Thanks :) . PIC working faster with CHE but USB SPEED don't .

Now I have 1MB in 3072 ms ~ 0,33MB/s  I need ~ 1MB/s

My configuration :

DLL version:    0.1.12.2
Driver version:    0.1.12.2

bus/device  idVendor/idProduct
bus-0/\\.\libusb0-0002--0x04d8-0x0204     04D8/0204
- Manufacturer : Microchip Technology Inc.
- Product      : Microchip Libusb Example Device
  wTotalLength:         32
  bNumInterfaces:       1
  bConfigurationValue:  1
  iConfiguration:       0
  bmAttributes:         c0h
  MaxPower:             50
    bInterfaceNumber:   0
    bAlternateSetting:  0
    bNumEndpoints:      2
    bInterfaceClass:    0
    bInterfaceSubClass: 0
    bInterfaceProtocol: 0
    iInterface:         0
      bEndpointAddress: 01h
      bmAttributes:     02h
      wMaxPacketSize:   64
      bInterval:        1
      bRefresh:         0
      bSynchAddress:    0
      bEndpointAddress: 81h
      bmAttributes:     02h
      wMaxPacketSize:   64
      bInterval:        1
      bRefresh:         0
      bSynchAddress:    0

What do you think about USB Device - MCHPUSB - Generic Driver Demo ? Can I  get ~1MB/s in this example?

There is bulk transfer in PIC32 Firmware.

Could you tell me more about :

to get maximum speed you should request more data before you've received previous data

For libUSB I use this code :

#include <usb.h>
#include <stdio.h>
#include <conio.h>
#include <Windows.h>


/* the device's vendor and product id */
#define MY_VID 1240
#define MY_PID 516

/* the device's endpoints */
#define EP_IN 0x81
#define EP_OUT 0x01

#define BUF_SIZE 1024
__int64 freq, start, end, diff;

int retVal, nBytes;
unsigned int mils,count;

usb_dev_handle *open_dev(void);

usb_dev_handle *open_dev(void)
{
struct usb_bus *bus;
struct usb_device *dev;

for(bus = usb_get_busses(); bus; bus = bus->next)
   {
     for(dev = bus->devices; dev; dev = dev->next)
       {
         if(dev->descriptor.idVendor == MY_VID
            && dev->descriptor.idProduct == MY_PID)
           {
             return usb_open(dev);
           }
       }
   }
return NULL;
}

int main(void)
{
   int i =0;
usb_dev_handle *dev = NULL; /* the device handle */
char tmp[BUF_SIZE] = {0};
char odb[BUF_SIZE] = {0};

usb_init(); /* initialize the library */
usb_find_busses(); /* find all busses */
usb_find_devices(); /* find all connected devices */
tmp[0]=0x80;

if(!(dev = open_dev()))
   {
     printf("error: device not found!\n");
     return 0;
   }

if(usb_set_configuration(dev, 1) < 0)
   {
     printf("error: setting config 1 failed\n");
     usb_close(dev);
     return 0;
   }

if(usb_claim_interface(dev, 0) < 0)
   {
     printf("error: claiming interface 0 failed\n");
     usb_close(dev);
     return 0;
   }
// start timer
QueryPerformanceFrequency((LARGE_INTEGER*)&freq);
QueryPerformanceCounter((LARGE_INTEGER*)&start);

for (;;)
{
retVal = usb_bulk_read(dev, EP_IN, odb, sizeof(odb), 5000);
if (retVal > 0)
{
nBytes += retVal;
}
if (nBytes >= 262144) break; // Break at 1MByte (1024 x 1024)=1048576
}

// stop timer
QueryPerformanceCounter((LARGE_INTEGER*)&end);
diff = ((end - start) * 1000) / freq ;
mils = (unsigned int) (diff & 0xffffffff);
printf("time %u ms\n", mils);


usb_release_interface(dev, 0);
usb_close(dev);

getch();
return 0;
}

Wow :) I get 955 kB/s  in 64kB buffer in PC libusb . Thanks chinzei, Deenyad .

In new microchip MCHPFSUSB Framework v2.5 there is example (WinUSB High Bandwidth Demo) with transfer 1MB/s :)) . Now, for me libUSb is more easy then WinUSB .

I use :
MCHPFSUSB Framework v2.5 for PIC32 , example - USB Device - LibUSB Generic Driver Demo
IN PC I write simple  c language program based bulk.c example in libUSB-win32

In PIC32 code I change clock to 80 Mhz and set CHECON register (sugesstion Deenyad :) )

Yes I based on a custom BULK transfer .

I sugesstion for you to look example WinUSB High Bandwidth Demo.