Which Harmony-compatible bankswitching gives most ROM/RAM?

[Sdw]

If I understand things correctly, the Harmony has 32kb of space for the cartridge ROM and 8kb of RAM.

However, there is no bankswitching method that uses all of these.

Which of the exisiting ones gives the best combination of ROM and RAM?

Looking at some charts of 2600 bankswitching methods, I'm guessing the E7/M-Network Bankswitch which seems to give access to 14kb of ROM and 2kb of RAM.

 

I've also read in the manual that custom bankswitching methods could be implemented in the Harmony. Is it theoretically possible to create some kind of super-bankswitch-method that gives access to the full 32kb ROM+8kb RAM?

Edited November 18, 2011 by Sdw

[+SpiceWare]

You won't get the full amount as the custom bankswitching driver itself takes up some room. The best so far is probably DPC+, which gives you 24K ROM + 4K RAM.

 

The driver that makes the DPC+ bankswitching work is 3K. The way it's configured you get 24K (six 4K banks) directly accessible to the 6507 and 4K of RAM (known as Display Data) that's accessed via the DPC+ registers. 4K of ROM holds the initial state of the Display Data, and another 1K holds the frequency data for the 3-voice music.

 

32K = 24K 6507 + 4K Display Data initial state + 1K frequency data + 3K bankswitch driver

 

The 3K driver is copied into RAM(as is the frequency data) as it runs faster from RAM and timing is very critical.

8K RAM = 4K Display Data + 3K driver + 1K frequency data

 

DPC+ also lets you use ARM code in your programs, an example of which is Frantic.

Edited November 18, 2011 by SpiceWare

[Sdw]

Thanks, that's good info!

 

But what if I want to have "normally" accessible RAM, that is RAM that I can actually put code in, access and modify with normal instructions (I like selfmodifying code ), the E7 is still my best bet?

[+SpiceWare]

3E might be an option. The format can handle up to 512K ROM and 32K of RAM (supported by the Krokodile Cartridge) Harmony supports up to 4K of RAM with 3E, I don't know how much ROM it supports.

 

For most RAM there's the Supercharger format, it has 6K. It doesn't have ROM per say, the Supercharger used audio cassettes to store the program and would load it into the RAM. It can load in additional code on demand, though it's not instantaneous. The Harmony emulates this by storing the code within the BIN file. I think up to 32K, but I think there's also some overhead to mark the code. I'm not familiar with how to code for the Supercharger, so you'd have to do some research if 6K of RAM sounds interesting.

[Sdw]

3E seems like a good choice. Frmo what I've found while searching threads here on the forum, Harmony should be able to handle 32kb ROM and 4kb RAM with 3E, which would be great!

However, I'm having a hard time getting it to work.

I've assembled a test-program, at the moment haven't even started on getting the RAM ($3e-writes) to work, just the normal $3f ROM-bankswitching.

In Stella, it fails if I just run it as a .bin (since it autodetects the wrong bankswitching) but if I manually set it to 3E using the "Game properties", it works as expected.

 

On my real 2600 with Harmony cart however, it doesn't work. With BIN extension, it fails to run at all, (diagonal lines) and with the extension as .3E it starts, but seems to set garbage in the registers (I get strange background color and a tone) and it locks up.

 

Here's my example:

 

.import source "vcs_base40.inc"

.var FRAME=$80
.var BANK=$81

.pc = $0000 "Bank1"
.fill    2048,$00

.pc = * "Bank2"
.fill    2048,$02

.pc = * "Bank3"
.fill    2048,$04

.pc = * "Bank4"
.fill    2048,$06

.pc = * "Bank5"
.fill    2048,$08

.pc = * "Bank6"
.fill    2048,$0a

.pc = * "Bank7"
.fill    2048,$0c

.pc = * "Bank8"
.fill    2048,$0e

.pc = * "Bank9"
.fill    2048,$0c

.pc = * "Bank10"
.fill    2048,$0a

.pc = * "Bank11"
.fill    2048,$08

.pc = * "Bank12"
.fill    2048,$06

.pc = * "Bank13"
.fill    2048,$04

.pc = * "Bank14"
.fill    2048,$02

.pc = * "Bank15"
.fill    2048,$64

.pc = * "Bank16"
.pseudopc $f800
{
   lda #$00
   sta $3f    
start:
   ldx #$00
   txa
clear:
  dex
  txs
  pha
  bne clear
frameloop:
   // Start of vertical blank processing
   lda #0
   sta VBLANK
   lda #2
   sta VSYNC
   lda #$00
   sta COLUBK

    // 3 scanlines of VSYNCH signal...
  sta WSYNC
   sta WSYNC
   sta WSYNC

  lda #0
   sta VSYNC		  

   // 37 scanlines of vertical blank...
   lda #127+44
   sta TIM64T
   
   // Do stuff
           
!wait:    
   lda INTIM
   and #$80
   bne !wait-
   sta WSYNC
           
  // 242 scanlines of picture...
  ldy #242
!loop:    
   sta WSYNC
   lda $f000,y
   sta COLUBK
   dey		         
   bne !loop-             

   // end of screen - enter blanking
  lda #%01000010
   sta VBLANK	      	     

   // 30 scanlines of overscan...
   lda #127+36
   sta TIM64T    
   
   inc FRAME    
   lda FRAME
   and #$0f
   bne !skip+
   inc BANK
   lda BANK
   cmp #$0f
   bne doit
   lda #$00
   sta BANK
doit:    
   sta $3f
!skip:    
       
   
!wait:    
   lda INTIM
   and #$80
   bne !wait-
   sta WSYNC

  jmp frameloop    
   rts   
   
}

.pc =$7ffa "Vectors"
   .word start // NMI
   .word start // RESET
   .word start // IRQ

 

And here's the layout of the assembled binary

Memory Map
----------
$0000-$07ff Bank1
$0800-$0fff Bank2
$1000-$17ff Bank3
$1800-$1fff Bank4
$2000-$27ff Bank5
$2800-$2fff Bank6
$3000-$37ff Bank7
$3800-$3fff Bank8
$4000-$47ff Bank9
$4800-$4fff Bank10
$5000-$57ff Bank11
$5800-$5fff Bank12
$6000-$67ff Bank13
$6800-$6fff Bank14
$7000-$77ff Bank15
$7800-$7867 Bank16
$7ffa-$7fff Vectors

 

The program *should* flash the screen in all the grey colors (with color data fetched from the different banks) and then finally in red before restarting. (this is all PAL btw)

 

Here's the compiled binary:

http://ag1976.com/tmp/3e.bin

 

What have I done wrong?

[cd-w]

I don't think Harmony can support 3E with 32KB - you may be able to get it to work by reducing the ROM usage.

 

Harmony has 32KB of Flash, but some of that is required for the bootloader and menu system. For normal 32KB ROMS (F4, F4SC), some of the RAM is used to compensate, but I'm not sure if that support was ever extended to 3E.

 

Chris

[Sdw]

Since my testprogram didn't use the extra RAM yet, I actually tried and renamed it to .3F instead, and then it worked on my Harmony.

So a 32k ROM with 3F bankswitching seems to work fine.

 

However, when running in 3E mode, it doesn't work. I tried dropping the size by removing two banks, giving me a 28k ROM, but it still didn't work.

 

I guess now we need someone with real insight to tell us how the 3E support in Harmony works!