From: cinap_lenrek@gmx.de
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@9fans.net>
Subject: [9fans] Tdmaxpkt in usbehci (no html)
Date: Thu, 11 Apr 2013 13:25:01 +0200 [thread overview]
Message-ID: <trinity-4dc553a9-048b-4476-b21b-57056db11e8e-1365679501436@3capp-gmx-bs34> (raw)
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?
--
cinap
PS:
sorry for the previous mail. i was sending it with web mail which i use very rarely
and the default setting for email was to send them as HTML :(
next reply other threads:[~2013-04-11 11:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-11 11:25 cinap_lenrek [this message]
2013-04-11 13:05 ` erik quanstrom
2013-04-11 13:09 ` kernel panic
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