PORTS Forum

Ports and Interfaces => USB => Topic started by: DaveB on February 22, 2012, 08:46:53 pm

Title: Configuration descriptor length vs max packet size
Post by: DaveB on February 22, 2012, 08:46:53 pm

Hi,

I have a config desc length of 67 bytes and the paket size for EP0 is 64 bytes.

I send the initial config desc 9 bytes when requsted and this contains the wTotalLenth field indicating 67 (bytes). The host gets this okay.

Now, what I cannot figure out is:

Does the host send multiple requests for the entire config desc (i.e. first request 64 bytes then 3 bytes) creating two interrupts,
OR
does it just request 67 bytes and I have to send two consecutive packets?

Thanks

Title: Re: Configuration descriptor length vs max packet size
Post by: Jan Axelson on February 22, 2012, 10:24:44 pm

One Get_descriptor request no matter how long the descriptor is.

If the Data stage has more data that will fit in one transaction, the stage uses multiple transactions (data packets).

Jan

Title: Re: Configuration descriptor length vs max packet size
Post by: DaveB on February 22, 2012, 10:42:53 pm

Thanks for your speedy reply Jan. :D