User:Myask/Universal Mapper Description Language

Needed features

Been thinking about making some better way to talk about mappers, as described in this post among several other places on our boards. Parts/functions

• Define state bits
  • include easy ROM/RAM chip(/internal) declaration; don't want to exclude MagicFloor nor MMC5/6 from "correct" description
• Logic
• Arbitrary address bus size for chips?

Convenience addtions

• Conditional operations (optional but helps user-side…but makes it harder program-side)
  • some header fields as parameters might be desirable (mirroring, chip sizes)
  • on the other hand, they are different boards in some manner. Perhaps only as solder-pad options?
• Cartridge connector pins as predefined signal names, or a module (to allow picking 60 or 72-pin)
• Option to autoconnect power, ground, address lines that are not in file
  • like connecting PPU_A[0:7] to CHR_ROM_A[0:7] if CHR_ROM_A[0:7] do not appear in the description)
  • Also autoconnect CIC

Extra function thoughts

• Outputs (e.g. LED)
• Inputs (e.g. DIPswitch, solder pads)
• Describing expansion port devices in similar manner
• Describing controller port devices in similar manner

Hard Part

• Expansion audio (analog, can involve extra oscillators as VRC7 audio does)

Specification

Comments

//c-style
/*and c-style*/
//Let's also treat all whitespace the same (except newlines terminating //, blocks)
//and "to" should be ignored in whitespace

Declarations:

mapper name begin
//contents
end name;

The outer part. Technically a block started with begin/end. Name optional.

mem name (address lines, data lines, writable, class);

• writable can be RAM or ROM.
• Class can be PRG, CHR, VRAM, [audio?] and MISC. Class controls default connections, and helps make obvious to readers what a thing is.

(see NROM example for default connections. Any prg gets CPU_A, CPU_D, /ROMSEL ("ROMSEL_n"), and optionally the R/W signal if it's a RAM. chr/vram gets PPU_A, PPU_D, read/writes, and enable depending on PPU_A[13] (or /A13 if VRAM)

solder name to /*contents*/; //can block if desired
dip name to /*contents*/; //can block if desired: same as solder for emulator

• dipswitch

Just different name, really both just a state-based if statement, and these state bits are not settable except hardware(emulator)-side, unlike…

register name; 
reg name;//short form

init name to value; //can refer to iNES header fields like mirroring

Not that iNES is something we want much of, but it'll cut down on file redundancy.

Statements:

connect x to y to z; //any size netlist, whitespace-separated
= x y z; //shortform
set name to value; //set a state bit
<= x y; //shortform

Operators

bitwise & AND | OR ^ XOR ~ invert
logical &&AND ||OR ^^XOR !not
mathematical + - * binary operations, -negation
{concatenate, concatenatee} [bus-index:range] {3 duplicate} //as in verilog

Execution blocks

on CPU_WRITE /*do stuff*/;
on PPU_WRITE
on CPU_READ
on PPU_READ
on CLOCK

Handy Shorthand Defines

bankreg name (which bus, width, address lines replaced, address mask selecting=equals what, which bus to write [inc A or D to write], mask to write=equals what,, written bits);
fixedbank (which bus, width, address lines replaced=with what, address mask selecting=equals what);

e.g.

bankreg bnrom (CPU, 2, 16:15, 16'h8000=16'h8000, CPU_D, 16'h8000=16'h8000, CPU_D[1:0]);

bankreg bxrom (CPU, 8, 22:15, 16'h8000=16'h8000, CPU_D, 16'h8000=16'h8000, CPU_D[7:0]);

bankreg gnrom_cpu (CPU, 2, 16:15, 16'h8000=16'h8000, CPU_D, 16'h8000=16'h8000, CPU_D[5:4]);
bankreg gnrom_ppu (PPU, 2, 14:13, 16'h2000=16'h0000, CPU_D, 16'h8000=16'h8000, CPU_D[1:0]);

bankreg magic_series_cpu (CPU, 7, 21:15, 16'h8000=16'h8000, CPU_D, 16'h8000=16'h8000, CPU_D[7:1]);
bankreg magic_series_ppu (PPU, 8, 20:13, 16'h2000=16'h0000, CPU_D, 16'h8000=16'h8000, CPU_D[7:0]);

bankreg unrom (CPU, 3, 16:14, 16'hC000=16'h8000, CPU_D, 16'h8000=16'h8000, CPU_D[2:0]);
fixedbank unrom_hi (CPU, 3, 16:14=3'b111, 16hC000=16'hC000);

The idea here is that it autogenerates a register of appropriate width, and statements in ON_x_WRITE to write that register when its write mask equality is met, and sets the appropriate address lines when its select mask is met. fixedbank does not need a register, obviously.

NROM-256 example

mapper NROM_256V begin
 //without autofills
 //aside from the mirroring, strikes me as the same as "default connections"?
//component section
 prgrom prg(32KiB); 
 //could also write 256Kib..but seems like a source of many typo problems
 //perhaps go by address line, data line counts?
 chrrom chr(8KiB);
 //only difference between PRG and CHR def'ns are its default connections
 //and outputs
 CIC cic(NES);//allow other chips I guess?

//dynamic components section
 solder h to connect CIRAM_A10 to PPU_A[10];
 solder v to connect CIRAM_A10 to PPU_A[11]; 
 init h iNES.6[0];
 init v ~iNES.6[0];
  //technically redundant per wiki as only V-using boards had solder pads?
  //make "to" as whitespace, allowing nice codelook but not requiring 
 connect CIRAM_CE_n to PPU_A13_n;

//connections: power
 connect VCC prg.vcc cic.vcc chr.vcc;
 connect GND prg.gnd cic.gnd chr.gnd;
  //allow multiple connections per statement
  //considering a shortform lke "=" for connect
//connections: CIC 
 //[omitted]
//connections: PRG
 connect prg.a[14:0] CPU_A[14:0];
 //NROM_128: connect prg.a[13:0] CPU_A[13:0];
 //and connect prg.a[14] VCC; //several ways to do it, really.
 connect prg.d[7:0] CPU_D[7:0];
 connect prg.oe_n prg.ce_n ROMSEL_n; //I suspect I've got these mildly wrong
//connections: CHR
 connect chr.a[12:0] PPU_A[12:0];
 connect chr.d[7:0] PPU_D[7:0];
 connect chr.oe_n chr.ce_n PPU_A[13];

end NROM_256V;