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• PS/2 keyboard controller

  Leon • 07/14/2019 at 23:30 • 0 comments

  At last I wrote a controller for PS/2 keyboard in the fpga. It has a 16 key queue.

  I was postponing it and was using an external board instead, but once I started, it was easy and fun.

• Memory block transfers

  Leon • 07/06/2019 at 14:52 • 0 comments

  I keep adding instructions that i think are useful or add speed as long as unused opcodes are available.
  

  I added ram block transfer commands. The IDX register that was used as a loop counter and index, is used by the transfer instructions to hold the number of words to be moved.
  Instructions MTOM, MTOI, ITOM, ITOI with two arguments An1,An2 move fast blocks of words starting from memory or IO address An2 to memory or IO address An1.

  Instructions NTOM, NTOI with arguments An1,N or An1,An2 fill the block pointed by An1 of size IDX+1 with the 16 bit value N (or An2).
  

      MOV A1,buffer1
      MOV A2,buffer2
      SETX 99
      MTOM A1,A2  ;copy the 100 words block starting at buffer2 to buffer1
      SETX 99
      NTOM A2,0   ;fill buffer2 with zeros

  These new instructions drastically improved scrolling routines speed
  

• Memory Pages in Lion

  Leon • 06/28/2019 at 13:53 • 0 comments

  When I first started to design the cpu I thought that 16bit address bus is ok for a homebrew cpu but after I made the Lion computer 64K rom+ram seemed very small although it used separate video and sprites ram. I wanted more memory and the more convenient way to do it is using pages. So I added 3 more address pins to lion cpu and added the necessary commands to support 8x64K pages.

  
  The SR register was extended from 8 to 16 bits and now the 9 most significant bits bit15 to bit7 hold the current code (bit15-bit13), data (bit12-bit10) and stack page (bit9-bit7).

  Instruction SDP sets the current data page, SSP sets the current stack page
  

  PJMP jumps to another address/code page.  PJSR jumps to a subroutine to another address/page and PRET returns.
  

  Also another register named OtherDataPage ODP assists in data transfers between pages by holding a source or target page for use with instructions PMOV PMOV.B
  

  Interrupt routines always use page 0 as a code page.
  

  I'm currently testing the functionality of this implementation and need to make more changes to the assembler
  

• Keyboard

  Leon • 05/24/2019 at 16:49 • 0 comments

  Fixed some issues with the keyboard, now Shift and Caps Lock work well, although I cannot turn the Caps led on due to the external controller board I use limitations. Maybe I have to build my own as i did with everything else although I find it not so interesting.
  

• Upgraded text mode 0

  Leon • 01/08/2019 at 15:17 • 0 comments

  Since I made a second video mode for graphics and added more vram I used the extra ram to also upgrade the first video mode for text so its now 640x240 pixels and with a 8x8 font can display 30x80 characters in two colors per character from 16 available.
  

• Second sprite controller

  Leon • 01/03/2019 at 16:19 • 0 comments

  Added a second parallel sprite engine so now 28 sprites are available for mode 1 in 8k sprite ram. It is synchronized using the vertical synch signal with the video controller that generates the first 14 sprites. Sprite ram is now split in two 4k independently addressed units so each sprite controller has its own ram. Sprite ram is mapped in I/O space at address 16384.

  I can any time easily add one or two more sprite controllers to have 42 or 56 sprites.
  

• 16 sprites

  Leon • 01/02/2019 at 21:54 • 0 comments

  Number of mode 1 sprites increased from 10 to 16.
  

• Older Logs

  Leon • 12/28/2018 at 13:18 • 0 comments

  Older project logs can be found in the first Lion project page at http://users.sch.gr/tliontakis/index.php/my-projects/13-vhdl-cpu
  

• Load screen & extended memory

  Leon • 12/25/2018 at 21:37 • 0 comments

  I added a INT 5, A0=13  system routine that loads in screen memory, files directly from the SDCard so I can easily display saved screens. Also I added a command LSCRN "filename", address in Tiny Basic.
  

  I added also a command XMOV in CPU/assembly that can move data to and from "extended memory" so now Lion can access more memory than the 64K ram (currently 128K). The "extended" memory can be used only for data not for programs.

  -- 28/6/2019 XMOV commands and extended memory no longer exist, they were replaced by page memory and commands
  
  

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