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;; Global variables used throughout the code base.
.scope Globals
;;;
;; Argument values as defined in https://git.mssola.com/nes/style.nes. Note
;; that these variables can also be used as temporary variables.
zp_arg0 = $90
zp_arg1 = $91
zp_arg2 = $92
zp_arg3 = $93
zp_arg4 = $94
;;;
;; Random values that can be used inside of functions for temporary values
;; so `zp_argX` variables are not overwritten as often.
zp_tmp0 = $9A
zp_tmp1 = $9B
zp_tmp2 = $9C
zp_tmp3 = $9D
;;;
;; Reserve a byte of memory for preserving indices on memory. This is needed
;; whenever the `x` and `y` registers might not be reliable because of
;; underlying `jsr` calls that might tamper with their values. Sometimes
;; saving the value in memory is enough instead of playing with the stack.
zp_idx = $9E
;; Flags that manage the state of the game.
;;
;; | Bit | Short name | Meaning when set |
;; |-----+------------+-------------------------------------------------------------|
;; | 7 | render | Game logic is over, block main code until NMI code is over. |
;; | 6 | ppu | PPU registers (2000 and scroll) have to be updated. |
;; | 5 | level | The current level is active. |
;; | 4 | column | The current column is still being buffered into the PPU. |
;; | 3 | end | We are at the end of the level |
;; | 2 | nametable | Next nametable to be used |
;; | 1-0 | - | Unused |
zp_flags = $20
.endscope
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