Semaphores in DSP/BIOS
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From: Tim Wescott on 29 May 2010 18:00 On 05/29/2010 11:23 AM, Randy Yates wrote: > Tim Wescott<tim(a)seemywebsite.now> writes: > >> On 05/28/2010 03:37 PM, Randy Yates wrote: >>> Thanks to everyone for your responses, but judging by the complexity >>> of your responses, I think you misunderstood my question. >>> >>> The main point is this: isn't there a "type" of semaphore usually >>> provided in other OSes which allows multiple tasks to pend on a >>> "single" post? >> >> Yes. It's called a 'binary semaphore'. Sometimes it's called an >> event' or a 'flag'. A complete RTOS should have both: many have just >> one or the other, along with some weasle-word justification for the >> practice that boils down to "we never need to use the other kind of >> semaphore and we're lazy, so you don't need to use it either". > > Ha! I hear ya' Tim. > > Well, it turns out DSP/BIOS _does_ have a "binary semaphore." The > problem is, it's not the type of binary semaphore I need. > > From the DSP/BIOS API Reference Manual for SEM_pendBinary(): > > SEM_pendBinary and SEM_postBinary are for use with binary > semaphores. These are semaphores that can have only two states: > available and unavailable. They can be used to share a single resource > between tasks. They can also be used for a basic signaling mechanism, > where the semaphore can be posted multiple times and a subsequent call > to SEM_pendBinary clears the count and returns. Binary semaphores do > not keep track of the count; they simply track whether the semaphore > has been posted or not. > > [...] > > If the semaphore count is non-zero (available), SEM_pendBinary sets > the count to zero (unavailable) and returns TRUE. > > If the semaphore count is zero (unavailable), SEM_pendBinary suspends > execution of this task until SEM_post is called or the timeout > expires. > > So what I need is not something that can handle multiple posts and one > pend, but rather something that can handle multiple pends and one post! MT! (that's the spelling) from US Software used to do that -- their binary semaphore (they called it an "event") had a 'regular' pend, and a 'check', where you could pend but not clear. I think it's Nucleus now, but I disremember. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Not Really Me on 3 Jun 2010 11:11
Randy Yates wrote: > Thanks to everyone for your responses, but judging by the complexity > of your responses, I think you misunderstood my question. > > The main point is this: isn't there a "type" of semaphore usually > provided in other OSes which allows multiple tasks to pend on a > "single" post? > > --Randy Wow, this may be stating the obvious, but there sure don't seem to be many DSP/BIOS users on here. -- Scott Validated Software Lafayette, CO __________ Information from ESET NOD32 Antivirus, version of virus signature database 5169 (20100603) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com |