Majsta's blog

Today I worked on this project for just 3 hours because I didn't have much time. Today goal was to investigate how to disable MC68000 from Amiga 600 board and replace it with TG68 core used by Accelerator board. So in this situation we will have Accelerator acting as a Master device. Key signals used in this operation are BR - Bus Request, BG - Bus Granted and BGACK - Bus Grant Acknowledge. After some research I found out that there are two ways to arbitrate the bus on MC68000 processor, 3-wire and 2-wire bus arbitration. So I needed to find out what type is used by Amiga hardware designers. Looking at Amiga 600 schematics I found out that BGACK is pulled high and that was sign to me that 2-wire bus arbitration can be used. Simple understanding of 3-wire bus arbitration is: Accelerator board activates BR, after that MC68K activates BG, Accelerator sends BGACK to MC68K. After everything is done on the Bus BR signals is deactivated, MC68K deactivates BG and Accelerator confirm that deactivating BGACK signal. In 2- wire bus arbitration BGACK is not used. I wanted to simplify this by taking BR and BGACK low because those are their active states and decided to ignore BG signal but that was not best solution su further investigation is needed here.

Hi I was wondering if you were still progressing on the board ? Maybe this could be turned into a full fleged Amiga if the rest of the chipset can be built into the FPGA or a different FPGA as well ?

Majsta: Thank you for the interest in this project. Testings stopped because I destroyed every single A600 board I had and destroy all of the Cyclone II FPGA devices. Those days I m working on logic analyzer capable of solving 5V inputs because there is no way I can repair those A600 boards without that. Board and everything was destroyed because of Analog and Digital GND problems and after some testings I m building new PCB version 1.2 who will remove those problems. It could be possible to have everything attached to accelerator board so board can act like standalone Amiga or Accelerator board for real Amiga but it could take time. First of all I need to connect to some people to accomplish this, but my idea was to have piece of hardware capable of emulating various cores and when time comes maybe platform could emulate even Natami or some other core. Situation for now is that Accelerator works stable at 7.09Mhz and that is important. After that it is only software thing to increase frequency as you like. When this piece of hardware become "open&source" I believe that smarter people than me will create faster cores at higher frequency's. After two years of testing here is the picture of working Accelerator board. Either way I received some money from donations and with those money I ll order new PCB and few Cyclone FPGA's for testings. Without those donations I wouldn't be able to continue so again THANK YOU ALL FOR UNDERSTANDING AND SUPPORTING THIS PROJECT.

Hi Again, I wrote the last question about progress, thank you very much for your quick answer, I am not used to people actually answering my dumb questions so fast and with many details. If you have time could explain to me the problem of Digital Ground and Analog Ground, I am not aware of any difference in grounds but maybe I missed something.
I am interesting in helping but I do not have any Amiga hardware yet.

Majsta: I ll provide anyone information's who are interested in this and similar projects but please register and use forum for this purpose because it is hard to talk this way. AGND is used for analog devices like voltage converters or something like that, DGND is used by digital devices like FPGA's, processors, voltage level translators or something like that. Basic procedure is to separate those GND's and use them on different layers connecting them at just one point or to create them on different parts of the board. If you work on this way components VCC's and GND's should know where to go to complete cycle. If you don't solve this properly there could be lot of bad influence on digital signals who can become distorted and unusable.

Today I worked on this project for just 3 hours because I didn't have much time. Today goal was to investigate how to disable MC68000 from Amiga 600 board and replace it with TG68 core used by Accelerator board. So in this situation we will have Accelerator acting as a Master device. Key signals used in this operation are BR - Bus Request, BG - Bus Granted and BGACK - Bus Grant Acknowledge. After some research I found out that there are two ways to arbitrate the bus on MC68000 processor, 3-wire and 2-wire bus arbitration. So I needed to find out what type is used by Amiga hardware designers. Looking at Amiga 600 schematics I found out that BGACK is pulled high and that was sign to me that 2-wire bus arbitration can be used. Simple understanding of 3-wire bus arbitration is: Accelerator board activates BR, after that MC68K activates BG, Accelerator sends BGACK to MC68K. After everything is done on the Bus BR signals is deactivated, MC68K deactivates BG and Accelerator confirm that deactivating BGACK signal. In 2- wire bus arbitration BGACK is not used. I wanted to simplify this by taking BR and BGACK low because those are their active states and decided to ignore BG signal but that was not best solution su further investigation is needed here.

After reparation of accelerator board for past two days I have done number of testings and changes in hardware design. Yesterday i discovered that clk signal from A600 board is not stable because ALVT devices had problems with GND and solved that. Also there was problems with PLCC-68 socket and address bus was not detected by the ALVT devices. Anyhow to realize those problems I had to write MC68K_probe tool in VHDL to test accelerator and signals from original CPU. After solving those problems I have working TG68 core on Accelerator board but there are lot of things to be done to get this working. First of all I need to disable original CPU to see that everything is fine with Accelerator. I know that I must take BR signal low but there are more signals that need to be handled to take over the bus from original CPU.

Again I destroyed another Accelerator board. In the process of using 7.09Mhz clock from Amiga board I was making some simple changes on the board and after that Cyclone was dead. Why? I just don't have explanation to this because I haven't done anything wrong here. Maybe static electricity or maybe that I didn't used Schottky diodes for protection but they are not used in most of the designs I have seen regarding to dev boards based on Cyclone devices. But in some devices they are used for Combining JTAG and AS Configuration Schemes but as I use only JTAG for testing without any Serial Configuration Device this also doesn't make any sense. So in this case there was no problems with overheating, short circuits and anything that I could done to destroy this device but again this stupid message:
!Error: JTAG chain problem detected
!Error: No device detected
Tomorrow I ll try to repair this board or use another Cyclone FPGA. Last one that I have!

Today major progress for me, for someone is nothing but after so much testing TG68 core is started :) Accelerator is programmed and core on accelerator is working somehow. Again like I said stupid reason RESET signal but again I want to say why someone didn't want to point me that there could be a problem... Testing continues :)

My project is related to Amiga and creating accelerator cards for Amiga computer. Why Amiga if we have modern computers, for those who are nostalgic those computers are important as air. So if you investigate there are lot of accelerators for Amiga but I m talking about creating worlds first FPGA Amiga accelerator, and I m working on this project more than 2 years. Idea is to create open hardware database, where everyone can build accelerator for their Amiga computers, also improve some characteristics and propose some ideas so we can bring old computers into life so they can act like modern computers supporting some new standards. Why, you may ask just because of that feeling you can't find with modern computers. You are feeling alive and able to accomplish anything, work with any part of that hardware, change it improve it, to be one with that hardware. Also that hardware I need to create is related to VHDL programing language so it can become also open software so anyone with some knowledge to VHDL can get higher speeds with that open hardware. At the end we can have old computers who can support anything like modern ones. So I think that this could bring something to large Amiga community and that they need that web site with open hardware and software for Amiga. Also i have major support from some large electronic companies because there are also some nostalgic people who would like to see my project is working. I had some offers to sold my schematics, codes to some German and American companies but I say no because this needs to be open hard&soft platform free for everyone who likes and lives for old nostalgic computers!!!