Wednesday, 31 January 2018

Creating some documentation on the MEGA65's enhanced text mode

This is a bit of a work in progress, but I have created some documentation for the enhanced text mode of the MEGA65. It is still missing the 256-colour mode information, but does explain the core of the memory layout when using 2 bytes per char instead of one.

Hopefully I will be able to expand on this over the coming week, however, this post also marks the end of my annual leave, and thus, sadly, progress will almost certainly slow down again for a while. That said, I am very happy with the progress made over the past six weeks or so. I tried to keep a bit of a progress log for my own personal satisfaction, and while I know I missed a bunch of stuff, it is still quite a list of things that have been dealt with:

24DEC17 - 800x600 video modes work
24DEC17 - Joystick input not working
24DEC17 - CPU bug fixed (Boulder Mark etc runs fine)
24DEC17 - b0 command in UART monitor stops CPU on BRK instruction
25DEC17 - $DC00 always reads as zeros
26DEC17 - Fix sprite fine horizontal placement problem
26DEC17 - PDM/Sigma-Delta audio output working
26DEC17 - Kickstart looks for file "NTSC", if not present, switches to PAL
26DEC17 - CIA clock speed is always 1MHz, except in C128 2MHz mode.
26DEC17 - Fix CIA clock halving bug
26DEC17 - $D016 smooth scroll in 320H mode fixed
26DEC17 - CIA is 1MHz even in 2MHz mode
26DEC17 - NumLock on PS/2 / USB keyboard is now "joystick lock" (WASD+shift, cursors+space)
27DEC17 - Got rid of single stray pixel by right border
27DEC17 - Make On-screen-keyboard X position variable via $D619
27DEC17 - C= + <- key to toggle matrix mode on C64 keyboards
27DEC17 - On-screen-keyboard again shows key events
28DEC17 - Stop kickstart screen format getting clobbered when setting PAL/NTSC
28DEC17 - Fix doubled first row of pixels in chargen/bitmap
28DEC17 - Joystick input on MEGA65 r1 PCB
28DEC17 - Stereo channel swap/merge on $D6F9
29DEC17 - Speed up PCB synthesis via map command line option
29DEC17 - Find bug stopping IEC serial working (was driving lines high)
29DEC17 - Find hardware errata; No SRQ line on IEC serial port
29DEC17 - Make joystick controlled quick-synthesising debug rig
29DEC17 - Right SID is now on right channel
29DEC17 - $D612 bits 6-7 allow rotation of joystick inputs by 180 degrees
30DEC17 - $D03x can no longer be written over in VIC-II mode
30DEC17 - IEC serial port works, at least partially
30DEC17 - Digital audio outputs reduced volume to prevent amplifier complaining
30DEC17 - Find and fix timer b and ISR reading bugs in CIAs
31DEC17 - Investigate and fix lack of shift register in CIAs for C65 DOS fast mode
31DEC17 - C65 disk drive check succeeds without shift-register status kludge
01JAN18 - VIC-II Bitmap mode displays last pixel row as though from next char row
01JAN18 - Fix trimming of sprite pixels vertically and when expanded horizontally
01JAN18 - Cartridge port accesses now work
01JAN18 - Cartridge ROMs now map to memory
02JAN18 - International Soccer cartridge works
03JAN18 - Ultimax-Mode cartridges work
04JAN18 - 1351/POT interface proof-of-concept
04JAN18 - 3.5" floppy drive proof-of-concept
05JAN18 - dotclock on cartridge port sped up from 4MHz to ~6.5MHz
06JAN18 - dotclock on cartridge port correctly at 8MHz
06JAN18 - 1351 mouse/POT inputs work correctly, and are in MEGA65 VHDL
07JAN18 - 16-colour sprite mode
07JAN18 - Sprite rendering bugs fixed
08JAN18 - Top row of pixels in sprite can now collide
08JAN18 - Sprite:sprite collision detection much more accurate (one Impossible Mission bug remains)
08JAN18 - Sprite Y position corrected
09JAN18 - Ethernet can received (but frames lack CRC!)
09JAN18 - 1581 repaired, and 3.5" test disks prepared
09JAN18 - Ethernet TX phase correction for r1 PCB (but CRC received by nexys still wrong)
09JAN18 - Ethernet TX and RX fully working on both r1 PCB and Nexys4DDR
10JAN18 - Resistor pull-up pack for floppy interface
10JAN18 - Floppy drive reads from real disk
10JAN18 - Worked out how to decode floppy data
10JAN18 - Real drive tracks F011 activity
10JAN18 - Step and spin-up delays set for real floppy drive
11JAN18 - MFM gap finder
11JAN18 - MFM gap quantiser
11JAN18 - MFM byte decoder
11JAN18 - 1581 sector decoder
11JAN18 - CRC16
11JAN18 - Real floppy mode for F011
12JAN18 - MFM decoder decodes real disks (but MEGA65 doesn't get the data for some reason)
13JAN18 - Amiga/1351 mouse / joystick auto detection
13JAN18 - Copy 1351 mouse status to Amiga mouse status to avoid mouse cursor jumping
14JAN18 - Fix problems with buffer writing when reading from FDC
14JAN18 - $14 F011 command waits instead of steps, as expedted
15JAN18 - Can load sector from FDC into sector buffer (but job doesn't complete properly)
15JAN18 - Ethernet MIIM now working
15JAN18 - FDC sector rotation bug fixed
15JAN18 - sector buffer collapsed to one physical copy (saves 2 BRAMs)
15JAN18 - FDC sector reading now works with C65 ROM (can DIR a real disk)
20JAN18 - Pull in Daniel England's diskmenu improvements
19JAN18 - Fix FDISK bugs for system partition creation
20JAN18 - Implement basic system partition reading
20JAN18 - Use CTRL,ALT and SHIFT to control boot process instead of FPGA switches
21JAN18 - Enhanced DMA list mode (and update FDISK, Kickstart to use it)
21JAN18 - Multiplier in CPU
21JAN18 - Hold RESTORE for HyperTrap, instead of double-tap (no stray NMI caused)
26JAN18 - Config program loads config from SD card
26JAN18 - Psygnosis owl sprite demo
26JAN18 - Fix logo display bug with new enhanced DMA
28JAN18 - Config utility works and saves and loads
28JAN18 - V400 character rendering bugs fixed
28JAN18 - V400 border position bugs fixed
29JAN18 - Virtual D81 F011 reading works again
29JAN18 - VD81 (buffered) writing seems to work

The main thing is that the hardware has been tested well enough to allow for the second revision of the motherboard to be designed and assembled over the next couple of months.

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