USB Communication in AT89C5131A

For AT89C5131A, Atmel has released a couple of USB device projects on Keil C51 on their website. This CDC implementation gives good starting point for your purpose.

USB Communication Device Class - Migration from RS-232 to USB
www.atmel.com/.../doc4322.pdf
www.atmel.com/.../c5131-usb-cdc-1_2_1.zip

You'll modify this example step by step.
1) run this example on your board
- This example supposes a 16MHz crystal. Tune it for your crystal

config.h
#define FOSC                    16000

Your board should appear as a CDC device on your PC.

2) Implement a loop-back, to test it on PC terminal.

if ( uart_usb_tx_ready() && uart_usb_test_hit() ) {
   char c = uart_usb_getchar();
   uart_usb_putchar( &c );
}

3) Replace the config descriptor into vendor-specific one, also VID/PID

config.h
#define DEVICE_CLASS          0x02  <-- 0xFF (vendor)
...
#define VENDOR_ID             0xEB03        /* Atmel vendor ID = 03EBh */
#define PRODUCT_ID            0x0920        /* Product ID: 2009h = CDC C5131 */
...
#define CONF_LENGTH           0x4300  <-- 0x2000
#define NB_INTERFACE          2       <-- 1
...
#define INTERFACE1_NB          1      <-- 0
...
#define INTERFACE1_CLASS       0x0A /* CDC ACM Data */  <-- 0xFF (vendor)

usb_cdc_enum.c
code struct
{ struct usb_st_configuration_descriptor  cfg;
  struct usb_st_interface_descriptor      ifc1;
  struct usb_st_endpoint_descriptor       ep1 ;
  struct usb_st_endpoint_descriptor       ep2 ;
 }
  usb_configuration =
  {
    { 9, CONFIGURATION, CONF_LENGTH, NB_INTERFACE, CONF_NB,
      CONF_INDEX, CONF_ATTRIBUTES, MAX_POWER},
    { 9, INTERFACE, INTERFACE1_NB, ALTERNATE1, NB_ENDPOINT1, INTERFACE1_CLASS,
      INTERFACE1_SUB_CLASS, INTERFACE1_PROTOCOL, INTERFACE1_INDEX },
    { 7, ENDPOINT, ENDPOINT_NB_1, EP_ATTRIBUTES_1, EP_SIZE_1, EP_INTERVAL_1 },
    { 7, ENDPOINT, ENDPOINT_NB_2, EP_ATTRIBUTES_2, EP_SIZE_2, EP_INTERVAL_2 },
};

Now that pyusb is able to see this device.

4) Lastly, clean up the source code.

Tsuneo

Hey Tsuneo,
Thank you for the informative reply. Unfortunately, I'm running the evaluation version of Keil uVision 4 and I'm getting a code size limit when I try to edit and compile the USB CDC project by Atmel. What's the best workaround here?
Is there some other compiler (like SDCC) which will work here?

Thanks,
Kalpesh Krishna

Hey Tsuneo,
I overcame the previous problem by using a PC having the full license. I successfully detected my device as a CDC device in pyusb.
However, I'm a bit unsure about step 2. I added something like this to my main()

while(1) {
   if ( uart_usb_tx_ready() && uart_usb_test_hit() ) {
      char c = uart_usb_getchar();
      uart_usb_putchar(c);
   }
}

Is this the correct place to write this code? On running this with pyusb, I get the following :- (131 is the endpoint address)

>>> dev.write(131, msg, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 870, in write
    intf, ep = self._ctx.setup_request(self, endpoint)
  File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 190, in setup_request
    self.managed_claim_interface(device, intf)
  File "/usr/local/lib/python2.7/dist-packages/usb/core.py", line 146, in managed_claim_interface
    self.backend.claim_interface(self.handle, i)
  File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", line 747, in claim_interface
    _check(self.lib.libusb_claim_interface(dev_handle.handle, intf))
  File "/usr/local/lib/python2.7/dist-packages/usb/backend/libusb1.py", line 552, in _check
    raise USBError(_strerror(ret), ret, _libusb_errno[ret])
usb.core.USBError: [Errno 16] Resource busy
>>>

Which is the correct place to put the code for step 2)? What are some good resources to learn the USB protocol from?

Thank you,
Kalpesh

Dear Tsuneo,
We were successfully able to transfer data to and from the microncontroller using pyserial. I think this code will be a great starting point for our application. Thanks for all the help!