From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfgang Denk Date: Mon, 01 Oct 2007 12:43:09 +0200 Subject: [U-Boot-Users] API for serial functions In-Reply-To: Your message of "Mon, 01 Oct 2007 06:20:49 EDT." <200710010620.50106.vapier@gentoo.org> Message-ID: <20071001104309.9753F2408A@gemini.denx.de> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de In message <200710010620.50106.vapier@gentoo.org> you wrote: > > i'm not claiming this is going to turn a 100mhz proc into 1000mhz proc or > something, but in the tail end of writing to the UART, you would free up the > CPU to continue ... and the processor tends to be a lot faster than the speed > of a UART, so it could chew through a sizable chunk of code before the UART > finishes shifting out a single byte ... and depending on the hardware, you > could be talking about 1 byte, 5 bytes, or more So you might end up saving 1 or 5 or a few more milliseconds. > maybe ... you'd have to mess up the processor pretty bad such that it breaks > the peripherals ... the UART in a Blackfin acts independently of the core > > > So I vote for not removing this transmitter empty check. > > i'd note that this is pretty inconsistent across different ports ... I agree with Stefan. Please don't change this. The current implemen- tation (wait until trasmit has completed) is what I prefer. > so when do you return ? after making sure the byte has moved from the core to > the peripheral hardware ? after making sure the byte has started to be > shifted out from the peripheral onto the line ? after making sure the byte > has been completed shifted onto the line ? the current Blackfin serial > driver exhibits the last -- it waits until the whole byte has gone through > the whole process, from core through the line If that's how it was implemented, then leave it that way. It's OK. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de Half of the people in the world are below average.