jacobson@uiucuxe.CSO.UIUC.EDU (08/06/86)
se interested here is some of the information I received with the memory card I received today in the mail at my dealers. This is the aMEGA card by C. Ltd. (formerly Cardco). As you can see it has the ground planes and they chose the Intel 8206 Ram controller because of reliability and the fact that it is available in low power CMOS version. Thus they have addressed the most important items given by Perry in his warnings about RAM cards. They do have wait states during RAM refresh that in Worst Case give you 4.5% slow down. But as they explain below that should only average 3% in memory intensive operations. Sounds to me like such small loss is entirely acceptable. Anyway I post this for your info and as a response to the very important questions raise by Perry. All in all the board is well constructed, and I am very happy with it. I hope this information will help those making choices in which card to go with. C. Ltd's card at this time is still the best buy and seems to be well-done overall in my opinion. aMEGA Board Instructions - by C. Ltd. - (316) 267-6525 The aMEGA Board - Design Perameters The aMEGA Board was designed to fully comply with the memory expansion methods designed by Commodore-Amiga for the Amiga Computer. Additionally, the board was designed to operate with the methods of memory expansion that are currently available,prior the Com##odore-Amiga's release of the full memory expansion software boot-up routines in Kickstart/WorkBench 1.2. All components on the board are socketed to facilitate repairs. The circuit board is a four layer board with full ground plane, and it is housed in a metal case to eliminate RF noise and interference. In genera# the board was designed using readily available components and proven, time tested, dynamic RAM design techniques. Automatic Memorv Confi#u#ation with Rev.1.1 Kickstart/Workbench To make a Rev.1.1 Workbench disk that allows the use of the ConfigMem (see AutoConfig) routine with the aMEGA Board you must boot up under Rev.1.1 Kickstart, then Rev.1.1 Workbench. Now copy the INSTALL:c/ConfigMem file from the aMEGA INSTALL disk to the c: directory of your Rev.l.l Workbench disk. Then you must copy the INSTALL:libs/ExpansionMemory file from the libs: directory of the aMEGA INSTALL disk to the libs: directory of your Rev.l.l Workbench disk. With these files on your Rev.1. 1 Workbench disk you can now call the ConfigMem routine from CLI ( or in your s/StartupSequence flie) just as you would any other command. Automatic Memorv Confiouration with Rev.1.2 Kickstart/Workbench Memory Configuration with Rev.1.2 is totally automatic and the routines are imbedded in the Rev. 1.2 Kickstart. These routines are not available to users. The aMEGA Board - Soeed of Ooeration and Wait-States The speed of operation of an Amiga external memory board is determined primarialy by the number of "wait states'' that are induced by the Dynamic RAM Controller IC chip. A ''wait state" occurs when the microprocessor is trying to read information from a memory location while it is being "refreshed''. Dynamic RAM chips will only store data for a short time, so they must be "refreshed'' periodically, ''refreshing" the RAM chips is one of the many functions performed by the RAM controller chip. The Dynamic RAM Controller is the one central component around which the entire RAM board is designed. While it is possible to design a custom RAM controller that induces no "wait states", we chose to use the very reliable, well proven and easily available single chip Intel 8206 RAM controller. Page 10 aMEGA Board Instructions - by C. Ltd. - (316) 267-6525 This RAM controller will induce some "wait states" but our decision to use it was based on our general design concept that some sacrafice in performance was acceptable in exchange for proven reliability and serviceability. The Intel RAM controller is a several year old product, with proven performance. The controller is easily obtainable to the general public in case a replacement is needed. And, this controller is available in a Low-Power CMOS version, which requires less power than other controllers (putting less demand on your computer's power supply) and produces far less heat than other controllers (which greatly increases the life expectancy of other components on the board). (Feel the case of the aMEGA Board during operation and you will notice very little heat build up.) As we said before a "wait state'' occurs when Your Amiga's central processor is trying to access the external RAM while the external RAM is being "refreshed". There are two factors that determine how often these collisions happen. The first is how often the RAM controller refreshes the RAM chips. Obviously, the more often these refreshes occur, the more often a collision is possible. With our Intel RAM controller, the time between refresh cycles can be determined by the designer of the board to fit the needs of the system. The Dynamic RAM chips available today are specified by thier manufacturers to be refreshed at least once every 4 milliseconds. P#freshing at this rate would cause a worst case slow down of about 1.##. We, following our general design philosophy of choosing reliability over raw speed, chose to refresh the RAM chips about 20# more often than the RAM chip makers require. This means that our board will have a worst case slow down of about 4.5%. This also means that as your RAM chips deterioriate with age and from heat build-up, our board will be refreshing them more often and this will considerably improve thier reliability and extend their usefull life. As we said this worst case slow down would be about 4.5%. The second factor that determines !:ow often "wait states" happen lowers this worst case number considera#ly. "Wait states" can onlv occur when the Amiga's microprocessor is tyring to read information located in external RAM. In normal operation the microprocessor ''fetches" a byte of data on during one clock cycle, then takes several clock cycles to process that information. Different instructions (ie. adding vs. subtracting - subtracting takes less) require a different number of clock cycles for the Amiga's microprocessor to do its internal calculations, so what the program is actually doing will change the number of "wait states'' that occur, because "wait states" onlv happen when the microprocessor is actually getting information from the external RAM. So, our worst case slow down is based on a program that is resident in the external RAM, uses short instructions (with few internal microprocessor operations) with all of its data in external RAM and all opertaions using the external RAM. In the real world this happens in only very, very few situations. A good question at this point is "O.K., in reality, exactly how much does this board slow down my Amiga?" Well, during graphics operations, screen updates and any operations that take place in the internal RAM of the Amiga, our board will not slow down your conputer at all! During very memory intensive operations like ''in memory sorting" and large spread sheet recalculations you may notice the worst case slow down (on the average of about 3%) during these operations. Based on our observations of typical use we would estimate the average user, would loose less than 15 seconds for each hour of computer use. Well thats about all I had, sorry about the mispellings, I missed them in the document which I used an optical scanner on. Does not always get the words right.