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[83.28.45.75]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3924f9484f1sm4728281fa.8.2026.04.29.04.58.35 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Wed, 29 Apr 2026 04:58:36 -0700 (PDT) Date: Wed, 29 Apr 2026 13:58:28 +0200 From: Michal Pecio To: Alan Stern Cc: Brent Page , linux-usb@vger.kernel.org Subject: Re: TT budgeting for EHCI; accommodate 1023-byte full-speed =?UTF-8?B?aXNvY2hyb25vdXPigJNpbg==?= endpoints Message-ID: <20260429135828.3e7f0675.michal.pecio@gmail.com> In-Reply-To: <20260429113604.2204b646.michal.pecio@gmail.com> References: <32291bf6-0c9d-4fd9-9dd7-489f7e1c9f02@rowland.harvard.edu> <20260429113604.2204b646.michal.pecio@gmail.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 29 Apr 2026 11:36:04 +0200, Michal Pecio wrote: > The host must schedule SSPLITs assuming no bit-stuffing to prevent TT > buffer underrun on long OUT packets. Assuming minimum/no packet headers > further minimizes downstream idle. TTs are required to buffer this. > > (BTW, periodic transfers should occur before async. Could the TT run > out of periodic, do async, then get an unexpected periodic transaction > in the next uframe? What happens?) > > Including packet headers for SSPLIT scheduling seems harmless unless > overestimated, but apparently it's not required. TTs must cope. Or maybe not, because 11.18.2 states that "budgeting" includes packet overhead and think time. And TT must handle gaps in periodic schedule due to short transfers and deal with not knowing whether there will be periodic transfers in the next uframe till the last moment.