That is what I had as well. I found that if I don't retry
usbd_ep_write_packet when it returns 0, I will sometimes have dropped
characters/lines. Retrying solves that if USB is connected, but goes
into infinite loop if it isn't.
Using cdcacm_set_config may work, if OSes always start a transfer on the
endpoint even if the terminal isn't open. I recall reading that at least
some OSes do that.
It seems to me like using DTR is the safest way, and it's actually only
a few lines of code, too.
Matthew
On 2015-11-09 12:07 PM, Jason Kotzin wrote:
> A bit of a hack, here is what I do.
>
> I usually put a static variable in the CDC file called usb_configured and
> initialize it to 0. When cdcacm_set_config is called, I set it to one.
>
> Then my main loop calls pop char, looks like this:
>
> static void pop_usb_char(void)
> {
> if (!usb_configured)
> return;
>
> if (!qempty(cdc->tx.head, cdc->tx.tail)) {
> if (usbd_ep_write_packet(iface, 0x82,
> &cdc->tx.buf[cdc->tx.tail], 1) == 0)
> {
> return;
> }
> cdc->tx.tail = qinc(cdc->tx.tail, cdc->queuesize);
> }
>
> }
>
> Works well, but wont work if the device is self powered, and you disconnect
> the usb and plug it back in.
>
> Hope that helps.
>
> Sincerely,
> Jason
>
>> On Nov 9, 2015, at 11:41 AM, Matthew Lai <[email protected]> wrote:
>>
>> Cool! That demo code does do that.
>>
>> I am not sure if it is completely compliant however.
>>
>> It implements SET_LINE_CODING and SET_CONTROL_LINE_STATE, but the
>> capability bit (0x2) indicates that we support GET_LINE_CODING as well.
>> The bit indicates support for these 3 requests (and a notification,
>> which we don't care about).
>>
>> There is no way to indicate support for only SET_CONTROL_LINE_STATE.
>>
>> And it seems like the only symbol missing (for implementing this) in
>> cdc.h is GET_LINE_CODING.
>>
>> I am not sure if GET_LINE_CODING is actually ever sent by Windows or
>> Linux, and whether not supporting it (despite setting the capability
>> bit) would actually be a problem.
>>
>> Thanks
>> Matthew
>>
>> On 2015-11-09 4:41 AM, Karl Palsson wrote:
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> Hrm, I thought the ti/lm4f cdc-acm demo code did this, but it
>>> might have it locally. The definitions from the standard would be
>>> certainly welcome in cdc.h
>>>
>>> Cheers,
>>> Karl P
>>>
>>> Matthew Lai <[email protected]> wrote:
>>>> Upon further research, I found that there is an optional "Set
>>>> Control Line State" request that does exactly what I want. It
>>>> is not yet implemented in cdc.h.
>>>>
>>>> I am going to implement it myself unless someone has done it
>>>> already?
>>>>
>>>> Thanks
>>>> Matthew
>>>>
>>>> On 2015-11-08 11:31 PM, Matthew Lai wrote:
>>>>> Hello!
>>>>>
>>>>> I am using CDC ACM as a debug logging interface, so sometimes there is a
>>>>> USB cable connected, and sometimes there isn't.
>>>>>
>>>>> My send routine looks like this -
>>>>>
>>>>> int ret = 0;
>>>>>
>>>>> do
>>>>> {
>>>>> ret = usbd_ep_write_packet(usbd_dev, 0x82, data, size);
>>>>> }
>>>>> while (ret == 0);
>>>>>
>>>>> However, if I call this function when either the USB cable isn't plugged
>>>>> in or serial monitor is not opened on the computer, usbd_ep_write_packet
>>>>> will just keep returning 0.
>>>>>
>>>>> Is there a way around this? Is there a way to tell whether the function
>>>>> returned zero because there is no receiver, or if it returned zero
>>>>> because it's busy and we should retry? Detecting whether the cable is
>>>>> plugged in (or even whether the device is enumerated) is insufficient.
>>>>>
>>>>> Thanks!
>>>>> Matthew
>>>>>
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>>
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