USB CDC-ACM function class

Revised above USB_SOF_Event() subroutine for bulk IN EP
This algorithm gives better transfer speed.

b) bulk IN EP

A typical implementation is,
In USB_EndPoint2() - always sends full (64 bytes) packet

USB_EndPoint2() ISR - USB_EVT_IN selector
- If the number of the data on the TX buffer is less than 64, return
- Check the FE bit of "Select Endpoint" command, if no empty EP buffer, return
- - WrCmd( CMD_SEL_EP(EPAdr(CDC_DEP_IN)) ); if ( CMD_DATA & EP_SEL_F != 0 ) return;
- Send 64 bytes from the buffer to the IN EP
- - USB_WriteEP( CDC_DEP_IN, TX_buffer, 64 );
- Raise a flag - flag_send_ZLP

In USB_SOF_Event(), call this subroutine

- Check the FE bit of "Select Endpoint" command, if no empty EP buffer, return
- send_cnt = number of data on the TX buffer
- if (send_cnt == 0) && (! flag_send_ZLP), return
- if send_cnt >= 64 bytes,
- - send_cnt = 64 bytes, and raise flag_send_ZLP
- else drop flag_send_ZLP
- Send specified number of data
- - USB_WriteEP( CDC_DEP_IN, TX_buffer, send_cnt );

Tsuneo

Good morning Tsuneo,

you suggested:
- Select the bulk OUT EP (USB_CTRL)
- Check PKT_RDY bit of RX_PLENGTH
- if not ready, return

Here is a part of my USB_ReadEP:

  USB_CTRL = ((EPNum & 0x0F) << 2) | CTRL_RD_EN;

  cnt = RX_PLENGTH;

  if ((cnt & PKT_RDY) == 0) {

    return (0);
  }

I return if the packet is not ready. The function is then called again in USB_SOF_Event () until a packet is ready and can be processed.

This solution doesn't work!
It seems that after selecting the endpoint I have to finish the operation.

Do you know what the problem is?

Thank you!
-Frank

Hi Tsuneo,

I tried to implement your suggested approach but noticed that there is a problem with the hardware.

I don't know if there is another way to implement this?

I would appreciate if you could answer to my described problem.

Thank you,
-Frank

Did you enable SOF (Start Of Frame) Event?

usbcfg.h
#define USB_SOF_EVENT 1

Tsuneo

Good morning Tsuneo,

I did enable SOF and verified in a debug session that the interrupt is working.

I think your description is the correct solution but the USB controller doesn't support your described behavior. This is at least what I was able to verify.

I can only spend limited time with this problem but I need to find a solution for this problem (our overall communication depends on this implementation).

Thank you!
- Frank

"I return if the packet is not ready. The function is then called again in USB_SOF_Event () until a packet is ready and can be processed."

I see, I remember the details of this engine.
Once RD_EN bit is enabled on the USB Control register (USBCtrl) to read out the Receive Packet Length register (USBRxPLen), we should read out the endpoint buffer, too. Then, we can't get the packet length without reading out the buffer. Inconvenient feature.

Then, instead of reading out the exact packet length, we have to assume it full length, 64 bytes. "Select Endpoint" command shows the buffer is empty or not.

a) bulk OUT EP
In USB_SOF_Event() (usb_user.c) [b]AND[/b] USB_EndPoint2() ISR - USB_EVT_OUT selector, call this subroutine.

- Check the FE bit of "Select Endpoint" command, if the EP buffer is empty, return
- - WrCmd( CMD_SEL_EP(EPAdr(CDC_DEP_IN)) ); if ( CMD_DATA & EP_SEL_F == 0 ) return;
- If the room on the RX buffer is less than 64 bytes, return
- read out to the RX buffer using USB_ReadEP()
- - USB_ReadEP( CDC_DEP_IN, RX_buffer )

Tsuneo

Oops, in above post,

CDC_DEP_IN ---> CDC_DEP_OUT

Tsuneo

"but never succeeded in reading FE bit status"

I mistakenly use WrCmd() in above posts. It is replaced to RdCmdDat() as follows.

a) bulk OUT EP
- Check the FE bit of "Select Endpoint" command, if the EP buffer is empty, return
- - WrCmd( CMD_SEL_EP(EPAdr(CDC_DEP_OUT)) ); if ( CMD_DATA & EP_SEL_F == 0 ) return; // - wrong

if ( RdCmdDat( CMD_SEL_EP(EPAdr(CDC_DEP_OUT)) ) & EP_SEL_F == 0 ) return;

b) bulk IN EP
- Check the FE bit of "Select Endpoint" command, if no empty EP buffer, return
- - WrCmd( CMD_SEL_EP(EPAdr(EPNum)) ); if ( CMD_DATA & EP_SEL_F != 0 ) return; // - wrong

if ( RdCmdDat( CMD_SEL_EP(EPAdr(CDC_DEP_IN)) ) & EP_SEL_F != 0 ) return;

Tsuneo

Hi Tsuneo,

thank you for your example.

- Frank