add debug pin, remove 2 unnecessary instructions

diff --git a/foo.S b/foo.S
index ff8453050b0ff22649e4924e5cb0a9f5d4331eb3..b65ac7d9ddacc7e07675a771207328ab248a519b 100644 (file)
--- a/foo.S
+++ b/foo.S
@@ -24,6 +24,7 @@
 /* I/O REGISTERS */
 OCR0AL = 0x26
 DDRB   = 0x01
+PORTB  = 0x02
 PUEB   = 0x03
 SPL    = 0x3D
 SPH    = 0x3E
@@ -116,17 +117,17 @@ g: ; g(i, t) -> t
        ANDI    t, 0x07
        MOV     tmp, i2
        ANDI    tmp, 3
-       TST     tmp
        CPSE    tmp, zero
        SUBI    t, -8
        #undef tmp
 
+       ;TODO: check correctness!
        #define tmp _
        MOV     tmp, t  ; NOTE: must move value away from `t`, as that is also hi(X)
-       LDI     Xhi, hi8(data)  ; TODO: can skip if &data < 0xff (it is)
+       LDI     Xhi, hi8(data)  ; hi(data) always zero, but still need to clear the register
        LDI     Xlo, lo8(data)
        ADD     Xlo, tmp  ;<-- the offset (formerly `t`) into data[]
-       ADC     Xhi, zero  ; ditto skip
+       ;ADC    Xhi, zero  ; data == 0x40  t <= 0x10, so can never overflow
        LD      tmp, X
        MOV     t, tmp
        #undef tmp
@@ -184,7 +185,7 @@ g: ; g(i, t) -> t
                test    3, m_1100
        m_0100: shift16
                RJMP    upper_8 ;'ll calc 0x84
-
+;TODO: combine shift16 above with add_shift16 below to save progmem
        m_1100: add_shift16
        upper_8: ; used twice, so deduplicated
                never   4
@@ -261,7 +262,8 @@ main: ; setup routine
        OUT     SPL, x      ; init stack ptr
        OUT     SPH, zero   ; -"-
        OUT     PUEB, zero  ; disable pullups
-       OUT     DDRB, one   ; PORTB[0] as output
+       LDI     x, 0x05     ; PORTB0:pwm, PORTB2:debug
+       OUT     DDRB, x
        LDI     x, 0xd8
        OUT     CCP, x      ; change protected ioregs
        OUT     CLKPSR, one ; clock prescaler 1/2 (4Mhz)
@@ -284,9 +286,11 @@ loop:
        RJMP    loop
 
 sample:
-       ; potential TODO: softcounter in r28 to only update duty cicle every n iterations
-       ; potential TODO: save/restore status register (SREG=0x3f)
+       ; potential TODO: softcounter in r25 to only update duty cicle every n iterations
+       ; potential TODO: save/restore status register (SREG=0x3f) (only if something in mainloop)
+
        OUT     OCR0AL, acc ; start by outputting a sample, because routine has variable runtime
+       SBI     PORTB, 2 ; to measure runtime
 
        MOV     n, i2
        LSL     n
@@ -439,4 +443,6 @@ sample:
        SBCI    i2, -1
        SBCI    i3, -1
 
+       CBI     PORTB, 2 ; end runtime measurement
+       ;TODO: to reduce jitter: clear pending tim0_ovf (TIFR0[TOV0] <- 1) ?
        RETI ; reenables interrupts