Unidirectional CDC option

[bremenpl]

Hello,
I am using the CDC device as a logger in my application. I am low on RAM resource and I would like to completely disable CDC RX functionality, as it is not needed in the application. I could not find any dedicated way for doing that. I have noticed that I can reduce the CFG_TUD_CDC_RX_BUFSIZE to a low value (even down to 0), but then the CDC TX parts starts to act in an unexpected way- the sent out data is being stalled until I reset the port (reopen) from the host side. I don't want to go into unnecessary details here, as maybe simply I am not using the CDC code part correctly.

In other words: What should I do/ call, in an application in which the CDC RX part is not needed and I don't want to read any data?
I would appreciate all help!

[bremenpl]

As the matter of the fact, weird things start to happen when I set the CFG_TUD_CDC_RX_BUFSIZE to less than 128. Once I do that, I notice that the tud_cdc_rx_cb is not being called anymore by the tusb stack. Going deeper with the debugger, I have placed a breakpoint in here:

https://github.com/hathach/tinyusb/blob/master/src/class/cdc/cdc_device.c#L435

If the CFG_TUD_CDC_RX_BUFSIZE >= 128, it is hit normally when I send a character over CDC. If its less, then this breakpoint is never hit.

So what I found coincidental, and that it seems to be true, is that the CFG_TUD_CDC_RX_BUFSIZE cannot be lower than CFG_TUD_CDC_EP_BUFSIZE... When I set both CFG_TUD_CDC_EP_BUFSIZE and CFG_TUD_CDC_RX_BUFSIZE to 127, then reception worked. Now leaving CFG_TUD_CDC_EP_BUFSIZE at 127 and reducing CFG_TUD_CDC_RX_BUFSIZE to 126 makes it stop working again. There is no correlation with CFG_TUD_CDC_TX_BUFSIZE however. So for example this is OK:

// CDC FIFO size of TX and RX
#define CFG_TUD_CDC_RX_BUFSIZE   	(64)
#define CFG_TUD_CDC_TX_BUFSIZE   	(128)

// CDC Endpoint transfer buffer size, more is faster
#define CFG_TUD_CDC_EP_BUFSIZE   	(64)

But not this:

// CDC FIFO size of TX and RX
#define CFG_TUD_CDC_RX_BUFSIZE   	(63) // <----------
#define CFG_TUD_CDC_TX_BUFSIZE   	(128)

// CDC Endpoint transfer buffer size, more is faster
#define CFG_TUD_CDC_EP_BUFSIZE   	(64) 

Going further, I started to wonder whether this line is by design: https://github.com/hathach/tinyusb/blob/master/src/class/cdc/cdc_device.c#L69

Because if I change 'CFG_TUSB_MEM_ALIGN uint8_t epout_buf[CFG_TUD_CDC_EP_BUFSIZE];toCFG_TUSB_MEM_ALIGN uint8_t epout_buf[CFG_TUD_CDC_RX_BUFSIZE];(so theepout_bufsize is the same asrx_ff_buf), I get no issues. It doesn't seem correct that rx_ff_bufandtx_ff_buf` sizes can be different, but not 'epout_buf' and 'epin_buf'.

I would appreciate all help in understanding this...