![]() Otherwise, the correct 8 or 16 bit value is inserted into the ROM buffer.įinally the header data is inserted and the checksum computed. If it is unable to resolve a symbol, it means it was never defined at all, and will throw an error. When all operations have been processed, the assembler revisits the symbol references found during iteration, and attempts to resolve them. The operations moveTo and inlineBytes move the assemblers internal offset and insert bytes directly into the ROM, respectively. When the assembler encounters an instruction that includes a symbol reference, it makes a note to revisit it after the operations have been processed - including the offset and symbol reference object - and moves the offset forward by the size required by the instruction. When the assembler encounters a label definition, if it hasn't already been defined, it associates the label name with the current offset. A label can be created with the label function, which returns a description of the label. Of course, there are also symbolic values like labels, references, and size calculations. At assembly time, the assembler maintains a buffer with an offset (starting at 0x150, the entry point located just after the cartridge header), and iterates through the operations, filling in opcodes and immediate values as it goes. One of the opcodes - 0xCB - is a "prefix", which opens up another 256 opcodes - which mostly provide single bit operations for the 8 bit registers, as well as some extended rotations, shifts, and swaps.Įach operation returns a description of the operation, along with any dynamic (immediate) arguments it takes. The SM83 CPU (which is a kind of a mix between a z80 and an 8080, but with some extra custom stuff thrown in the mix) has 256 opcodes, of which 11 are considered are undefined and will lock up the CPU. If you're curious about the exact transformation from JSON to TypeScript, check out the scripts/ops-generator.ts file this repo. For example, 40 overloads are generated for the LD instruction. In TEGA, the only name of the operation and its opcode are needed to generate overloaded, type safe function definitions for each assembly instruction. This file is used to generate the excellent gbops website, which provides a highly detailed opcode table for the GameBoy, with tons of useful information like cycles take per op, memory operation breakdown per cycle, etc. TEGA generates the function definitions for all of the assembly operations automatically based on the dmgops.json file in izik1's gbops repo. There is a video that goes into some depth about TEGA and Block Jump on the Low Byte Productions YouTube channel. This game is based on the dinosaur jumping offline game in google chrome, and features, amongst other things: A Game Example: Block JumpĪ full game example can be found in. This means that you can easily generate code using all of your favourite libraries like lodash and ramda. It also provides facilities for creating type safe abstractions (macros) using all the regular language features of TS. It exposes a type safe API for all SM83 assembly instructions, defining inline bytes (in the form of TypedArrays), moving around in ROM space, and symbols, as well as definitions of the memory map layout, hardware registers and their important bitfield postitions (based on hardware.inc). TEGA is a TypeScript library (also usable in JS) for programming and creating GameBoy ROM images that can be played in an emulator or on real hardware via a flashcart. TEGA: TypeScript Embedded GameBoy Macro Assembler
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