1. I think load lock instructions handle that now 4. M9S12 doesn't. I disable interrupts. Don't allow DMA to mutex variables
Sent from John's iPhone 4S On 2019-07-27, at 11:21 AM, Chris Albertson <albertson.ch...@gmail.com> wrote: > There is a LOT more to this. > > 1. Dual or multi-core CPUs add some complexity because all the CPUs share a > common memory. What if all four CPUs try to run the "test and set" at the > same time? Also, you can no longer assume an interrupt handler has > exclusive use of memory. > 2. what if the process uses two queues? Process A might hold access to > Queue X and process B holds Y and then each waits for the other process to > release the other queue and the system deadlocks. > 3. what if there are more than two processes? How to ensure that access to > the queue is fairly sharded between four or six users? > 4. What if the CPU you are using lacks a test and set instruction? > > There are good solutions but today NO ONE has to solve these problems > solutions were worked out 50 years ago. > > On Sat, Jul 27, 2019 at 10:22 AM John Dammeyer <jo...@autoartisans.com> > wrote: > >> So true. Most RTOSs have both Semaphore and Mutex features. >> >> Even a simple Test and Set instruction where if the location is set the >> resource isn't available are easy to use. For the non-comp sci people the >> Test and Set looks at the location and sets or clears the Zero flag before >> setting the location to 1. If the location was already 1 then the zero >> flag is set to FALSE. If the location was 0 it will be set to 1 with the >> zero flag set TRUE. The next step of the program then tests the zero flag >> to determine if it now has exclusive use of the resource or if some other >> task/thread was already using it. >> The test and set cannot be interrupted and the location cannot be modified >> by DMA (direct memory access) from another hardware device. >> I don't know if the ATMEL device used in the original Arduino has that >> capability. But the bigger processors all pretty well do. >> >> John >> >> >>> -----Original Message----- >>> From: Chris Albertson [mailto:albertson.ch...@gmail.com] >>> Sent: July-27-19 8:58 AM _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
