And Controlled Schools Responses Received To The: Fill & Download for Free

This started as a reply to this comment, but quickly grew into something larger.Are you asking why we tend to use distinct wires for address, data, and control, or why we depict these as three parallel buses?For an old-school 1980s style asynchronous, non-multiplexed bus, the address, data, and control effectively form one large, parallel bus. However, each of the three pieces, address, control, and data, become valid at slightly different times. In fact, who drives the bus varies between reads and writes. On a write, the CPU may drive address first, then control, then data.Here’s a Z80’s read and write cycle:Notice that for a write, the address goes out first, at the rising edge of T1. Then ~MREQ is asserted (goes low) at the falling edge of T1, along with the write data. (~MREQ is there to allow external logic to assert wait-states.)The actual write doesn’t occur until ~WR goes low at the falling edge of T2, and is complete at the falling edge of T3. The address and data then fade from the bus at the rising edge of T3.For a read, it’s even different. The CPU asserts ~MREQ and ~RD together, but doesn’t look for the read data from the memory until just before the falling edge of T3. And, notably, the memory drives the data, not the CPU.Logically, the three buses do different things. And, typically, different logic looks at each of these three. Address decoders don’t look at the data bus, for example, although they might want a ‘valid’ indication from the control bus to qualify their computation at the end.Now, you could multiplex these things. LPDDR4, for example, multiplexes address and control over a 6-wire bus, but keeps the data bus separate, so you can pipeline commands ahead of the data and reduce latency over the narrow, high clock rate channel.Likewise, as Robert Wessel noted to you in his comment, PCIe combines all of these—command, address, data—onto one common bus, packaging up memory requests into TLPs that are sent serially over high speed serial links. And, I’ve heard of on-chip buses that perform similar packetization to reduce the amount of wiring on a chip.The plus side is that it reduces wire count. The downside, as Robert noted, is that it can add latency to packetize and de-packetize these requests, even if you manage to keep the bandwidth up.There can also be good reasons separate them, or perhaps combine the signals differently than simply “address”, “data”, and “control”.For example, the AXI4 protocol actually has five channels: AR, AW, R, W, and B. I hear you say “What?” Here’s what the four channels are:AR channel: Read commands. Includes address and control information.R channel: Read response. This includes data and some control metadata.AW channel: Write commands. Includes address and control information.W channel: Write data. This includes the data, and some control metadata.B channel: Write response. This is primarily success/failure completion information.Why so complicated? Because AXI wants to go fast.AXI lets you get multiple commands in flight from a single requestor. You don’t have to wait for the previous request to complete before you start your next request. You can get as many requests as you like in flight, until the AXI interconnect drops its ‘ready’ signal. This allows you to generate a pipeline of requests and achieve high bandwidth, despite high latency in your memory system.You can fire off a bunch of read requests into the system on the AR channel, and over time, those requests will filter back to the requestor on the R channel. Likewise, you can fire off a bunch of write requests on the AW channel, and as the system is able to accept write data, push the writes out separately on the W channel. As the write complete, the completion information filters back in the B channel. (And in AXI, the read and write channels operate fully independently.)Having a separate command vs. data channel on writes allows the interconnect to decode addresses ahead of receiving the data, so it can steer write data where it needs to go with less overall buffering. Read response doesn’t get that benefit; however, the read response metadata contains an ID that the interconnect uses to quickly look up and route the response.You’ll note that I call these channels rather than buses. Old-school buses are broadcast affairs. The CPU (or a DMA controller) broadcasts an address and a read/write indication, and everyone sees it. AXI, on the other hand, doesn’t work that way. Rather, each AXI interface connects exactly two things: a master and a slave. Masters include things such as CPUs and DMA engines. Slaves include memories and peripheral registers.Now, you might wonder how you can connect more than two things in such a system. That’s where the interconnect comes in.An AXI master such as a CPU usually connects to a slave port on an AXI switch (such as a NIC-400 or CCI-400). That switch then decodes the address information and routes the request to a master port on the AXI switch, which then drives the request downstream to another AXI slave. In a simple system, there’s one AXI switch, with all of the masters on one side, and all the slaves on the other. In a larger system, there could be multiple switches.It’s no longer a broadcast affair. It’s a switching fabric that connects all these pieces.You’ll notice that the inputs to the interconnect on the left are called slave interfaces. This is what you hook your masters to. The outputs on the right are called master interfaces. This is what you hook your endpoint slaves to.The separate channels provide a high degree of concurrency, then, between different requestors and different target end-points, with the switches in-between handling the routing for all of the in-flight requests.The read and write data channels are separate from the read and write command channels, because commands only take one cycle to hop from master to slave, while data may take multiple bus cycles. For example, a 64B write on a 16B wide bus takes 1 cycle to issue the command, but 4 cycles to move the data. By keeping the command channel separate, the requestor can fire off a new request to a different endpoint early without waiting for all of the data to move.As you can see, when you get further in, it actually gets more complicated than the simple “address”, “data”, “control” triumvirate.The right tradeoff will vary by system, based on the performance and cost targets, and the available technology at the time when it’s built.

Thanks Judith for your question. By the time my son was a freshman in high school he had already been expelled from two Catholic grade schools. We had already moved twice because of his behavior. The summer before 6th grade my son had discovered public transportation and it became a unwindable game of hide and seek. The divorce decree prevented me from moving more than 50 miles away.I found a small town which was within the boundaries and was approximately 30 miles from any public transportation.There were plenty of activities for my son to enjoy so we moved there before he began the 6th grade.When he entered into high school he began frequently skipping school. As a single parent who didn't receive child support I had no choice but to work a full time job.My ex husband is a narrisst and he used my son as a pawn to punishh me for divorcing him. He some how managed to manipulate the system and was never held accountable for not only failure to support his son but also for the many negative people and things which he subjected my son to during his court ordered visitation. He undermined everything positive in my sons life. Not only was my ex husband manipulating the court system, the school system and even the therapists that I had working with my son, he manipulated my sons desire for his love to the point that my son would do anything for the few crumbs of "love" he could receive from dad. Needless to say everything I would try to do to help my son became an uphill battle at every turn.The principal called a meeting to discuss the truancy situation. After the first meeting with the principal I had begun walking my son into school and to his homeroom making sure that the teacher was aware that he was there.My thought at the time was not only to stop my son from skipping school but I had also hoped that my son would be embarrassed by the fact that his mom was escorting him to class everyday. I mean what teenager wouldn't be embarrassed to have his mom walk him to homeroom? Well it didn't matter to my son!After homeroom my teen would then slip out of school! With his dad waiting for him to go and hang out!I soon was summoned back to the principals office. The principle then said that he was going to report me to child services for neglect because of my sons lack of attendance.This really was the straw that was about to break my back! I was doing everything within my power to provide my son with a positive environment and to end this cycle of poor behavior. I had him in counciling, had his free time occupied with team sports, had him in a mentoring program along with therapy. My life was centered around providing a positive environment for my son to grow and thrive in a respectful manner. Although he always spoke with respect he was rewarded by dad for any action in which he would disrupt the positive influences that I was working so hard to provide.When the principal had threatened to have charges brought against me (they were aware of the situation with his dad) I said to the principal " I make sure that he is here everyday. I should not be punished because you (the school) are unable to keep him here!"This seemed to make no difference to the principal. He then said that I was still responsible fotr my sons attendance and if he continued with this behavior that I would be the one who would be charged with child neglect because my sons actions were my responsibility not the schools. I then told the principal that he was wrong and it was the schools responsibility to make sure that my son remained at school during the school day. That the schools responsibility was his to oversee once the student was at school. That he was responsible for my sons whereabouts and wellbeing while in the schools custody.I then asked the principal what does he expect me to do? If I didn't have to work I would escort my son from class to class. If I changed jobs and worked the night shift in order for me to ensure that my son remained at school for the entire day, then I would certainly be neglectful if I left him home alone at night. I was in a no win situation. Both my parents were dead, I received no support from his dad. I was at a complete loss as to how I was supposed to solve this problem?Needless to say that the school was not interested in helping me control my sons behavior or to even work with me concerning the situation.This left me with only two options. One was to give custody to my ex husband to be in an environment in which he would have no positive supervision where the examples set were ones in which drugs were prevalent. The only other option was to put my son in boarding school. This was the best option of the two and it was the one that I was forced to choose.Had I have had support from the public school system and from his father my son would have been able to learn that he had a responsibility to attend school and respect the adults who were to teach him and hold him accountable for his behavior while he was in their custody.I remained steadfast to teach my son right from wrong and after years of dads manipulating games my son has learned the hard way to be a responsible man. Sadly he wasted almost two decades of his life learning that mom was right after all.Our job as a parent is to never stop trying to teach our children to become responsible adults. I would suggest that you be the positive example to your child and stand up to the school in defense of your child if you are positive that you are correct and that the school is not behaving in your child's best interests. The example you set may not come to fruition for years but if you remain determined to be the best example for your child, your child will eventually see that you had their best interests in mind. At the same time you must also be humble enough to show your child that you are able to admit if you have made a mistake. That standing up for what's right no matter how hard it may be is the true meaning of integrity.I'm not sure if I have answered your question or not. I can only hope that you will find my answer helpful. Good Luck!

Speaking from the perspective of a U.S. cop, there are several areas with significant differences. I should point out that I've never been to the UK, but have read a lot about this issue and discussed it with cops and non-cops in the UK.I believe the most critical difference is the amount of training required of UK police. New hires attend a "police college" course of several months before going into the field to work for another few months under close supervision (sorry, I don't have the precise durations here, but it's considerably more training than most U.S. police receive). They then return to the police college for several more weeks until they are assigned to their duty stations. From here, on-the-job training is similar to that in the U.S., where the new constable works with a senior partner for several months before he is given a solo assignment. He is still closely supervised and his performance reviewed frequently for his first year to two years of service.Keep in mind that this constable carries no firearms, and if he drives a vehicle at all, it will be a small car not intended for sustained highway speeds. He does not get involved in vehicle chases or even do a lot of traffic enforcement. Constables are typically equipped with Speedcuffs (a type of handcuff with a rigid connector between the two links, as opposed to the flexible chain typically used by U.S. police), a collapsible baton, and pepper spray or tear gas. This equipment is a relatively recent innovation. For many years, the only equipment the constable carried other than his uniform and possibly a radio was a "truncheon," a short wooden baton.If the new constable aspires to be the equivalent of a highway patrol officer or state trooper, he first completes several qualifications for driving increasingly powerful vehicles, with a gap between each qualification to assess performance. If he is selected for highway patrol (they call it something else) training, the course is about a month long, and not everyone passes. The vehicles they drive for this are comparable to U.S. highway patrol cars. The final exam is to pursue another police vehicle at high speeds on an open public roadway in typical traffic, with an instructor in the passenger seat. The pursuit might be 20-30 miles in duration. The candidate driver gives the instructor a running account of what he is doing and why during the entire course of the pursuit. The fact that the British even tolerate this is testimonial to the level of confidence and support they have for their police.There is an excellent video of one of these pursuit driver final exams here:A driver qualified for pursuits with motorcycles and cars has over 680 hours of training devoted exclusively to driving. (http://www.driveandstayalive.com/articles%20and%20topics/police%20issues/police-driving.htm) The typical U.S. police officer has maybe 40 hours of driver training, more if he is employed by a state police or highway patrol.Constables who carry firearms, called Authorised Firearms Officers or AFOs, are selected even more carefully and have years of experience before they can even apply. Many are already qualified as pursuit drivers because the Armed Response Vehicles (ARVs) they operate have to respond quickly and sometimes over significant distances. Prospective AFOs first spend a week becoming familiar with the 9mm Glock pistol and H&K G36 or 416 carbine. This is a qualifying/selection course. Those who make the grade spend another six weeks in tactical training. Once qualified, they attend one full day of firearms refresher training each month and a two-week course each year. When on uniformed patrol out of a car they will always be carrying a holstered pistol and their long arm on a slinged carry. ARV crews have to be in superior physical condition, and an injury or weight gain usually means leaving that unit, at least temporarily. SFOs (Specialist Firearms Officers) are even fitter. Some AFOs also carry TASERs. These are not also carried by regular constables, with a number of people per shift carrying them.U.S. cops get 40-80 hours of firearms training in the academy, and may not actually train with their weapons again for years. They do qualify periodically (sometimes as infrequently as once per year) in a marksmanship course of 50 rounds or so, but those who fail to pass typically just repeat the course until they qualify. Most U.S. police agencies regard the ammunition necessary for firearms training to be too expensive to provide regular firearms training. U.S. police carry their firearms all the time, on duty and off, and need no supervisory authorization to deploy them.There are other aspects of UK police training that are far superior to what police typically receive in the United States. For example, riot control (they call it "public disorder") training includes a mock riot where instructors are throwing half-bricks and live Molotov cocktails (gasoline bombs) at the trainees.I'd like to see U.S. police training upgraded to something closer to the British model, but given the state of public sector budgets, I don't think this is likely in my lifetime.Edit 1/14/19—added comment by Ian McDonald: When as an elected councillor, I attended the London Metropolitan Police firearms school for a day. They use a system where film scenarios are screened on a gun range and police officers have the option of firing and freezing the frame. Officers are trained to fire only when necessary and a bigger danger to the public. Usually they will talk an offender down. In real life, rounds are counted out at the start of a patrol and in at the end. If there is a round shot or missing the officer is suspended, pending an inquiry. Consequently an officer is held responsible and is expected to use firearms with considerable care.