From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Thu, 11 Apr 2013 09:05:57 -0400
To: 9fans@9fans.net
Message-ID: <89ec832d7e467386a2f36d83033d0c6b@kw.quanstro.net>
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Subject: Re: [9fans] Tdmaxpkt in usbehci (no html)
Topicbox-Message-UUID: 40cce680-ead8-11e9-9d60-3106f5b1d025

> in the ehci driver, it uses:
>
> Tdmaxpkt = 0x5000, /* max buffer for a Td */
>
> a td has 5*4K pages giving the 20K above, but i think this only applies if the
> first pointer is page aligned (page offset = 0) so all the pages can be filled
> completely.
>
> The EHCI spec says this:
> "The buffer pointer list in the qTD is long enough to support a maximum transfer size of 20K bytes. This case
> occurs when all five buffer pointers are used and the first offset is zero. A qTD handles a 16Kbyte buffer
> with any starting buffer alignment."
>
> The buffer pointer isnt page aligned as far as i can see, so make Tdmaxpkt = 0x4000 instead?

i wonder if it would make more sense to align the buffer.

(the unaligned case for iso->data looks wierd, too.)

- erik