Use POKEY for random seed on Atari

CHANGELOG.md

@@ -10,6 +10,8 @@
 
 * Implemented `readline` and `readword` for VIC-20.
 
+* `init_rand_seed` uses the POKEY on Atari.
+
 * Fix: more instances of memset loops should be detected and optimized (#59).
 
 * Fix: things mentioned in the segment layout should not be deleted even if unused.

docs/stdlib/other.md

@@ -32,6 +32,8 @@ Current implementation:
 
 * On C64, spends two frames reading noise data from the SID chip.
 
+* On Atari computers, reads the POKEY random register.
+
 * On Z80, reads the refresh register.
 
 * On all other targets, sets the seed to 1.

include/m6502/random_6502.mfk

@@ -33,6 +33,21 @@ void init_rand_seed() {
     rand_seed.lo = peek($D41B)
 }
 
+#elseif ATARI_8
+
+noinline asm void init_rand_seed() {
+    lda $D20A
+    sta rand_seed.lo
+    lda #1
+    .loop:
+    asl
+    bne .loop
+    lda $D20A
+    sta rand_seed.hi
+    rts
+}
+
+
 #else
 
 inline void init_rand_seed() {