v0.3.0

Author: nerdralph

README.md

@@ -3,10 +3,10 @@ This library replaces Arduino AVR Core functions with smaller and faster version
 For example, the Blink example sketch built for the Uno takes 924 bytes of flash, but only needs 196 bytes with ArduinoShrink.
 
 ## Usage
-Download [a release](https://github.com/nerdralph/ArduinoShrink/releases), and extract the files into your Arduino/libraries folder.  Select ArduinoShrink from the Sketch, Include Library menu.  This will replace pinMode, digitalWrite, and digitalRead with much smaller and faster versions.  The Arduino pin number must be known at compile time if you are using this library.
+Download [a release](https://github.com/nerdralph/ArduinoShrink/releases), and extract the files into your Arduino/libraries folder.  Select ArduinoShrink from the Sketch, Include Library menu.  This will replace several Arduino functions with smaller and faster versions.  The Arduino pin number must be known at compile time if you are using this library.
 
 ## Limitations
-ArduinoShrink implements a simple millis timer, but does not implement micros.
+ArduinoShrink supports only ATmegax8 MCUs running at 16Mhz
 
 ## Development plans
-Future versions will include support for 8Mhz clock rate.
+Future versions will support 8Mhz.

src/micros.S

@@ -10,8 +10,8 @@
 ;    uint8_t ovfl_pad;
 ;} t0_millis;
 
-; ensure timer ISR is brought in by linker
-.global t0_ovfl_inc
+
+;.global lsl4_r22_r30
 
 .global micros
 micros:
@@ -24,5 +24,7 @@ micros:
     ldd r25, Z+2
     in r0, TCNT0
     sub r0, r22                         ; TCNT0 overflow?
-    brne 1b
+    brcs 1b
+    ldi r30, 2                          ; multiply by micros/tick
+    rcall lsl4_r22_r30
 ret

src/millis.S

@@ -8,8 +8,8 @@
 ;    uint8_t ovfl_pad;
 ;} t0_millis;
 
-; ensure timer ISR is brought in by linker
-.global t0_ovfl_inc
+; to force t0_isr to get linked in
+.global lsl4_r22_r20
 
 .global millis
 millis:
@@ -22,4 +22,25 @@ millis:
     ld r0, Z
     cp r0, r22                          ; has millis changed?
     brne millis
+    ; millis = t0_ovfl * 1.024 , so multiply by fractional addition
+    movw r18, r22
+    movw r20, r24
+    rcall shift_add                     ; adds t0_ovfl / 128
+    rcall shift_add                     ; adds t0_ovfl / 64
+    ; rcall 1f
+    ; todo: add t0_ovfl / 2048
+1:  add r18, r24                        ; adds t0_ovfl / 16384
+    adc r19, r25
+    adc r20, r1
+    movw r22, r18
+    movw r24, r20
+ret
+
+shift_add:
+    ldi r30, 1
+    rcall lsl4_r22_r30
+    add r18, r23
+    adc r19, r24
+    adc r20, r25
+    adc r21, r1
 ret

src/t0_ovfl_isr.S

@@ -8,9 +8,6 @@
 ;    uint8_t ovfl_pad;
 ;} t0_millis;
 
-; so timer ISR is brought in by linker when needed
-.global t0_ovfl_inc
-
 .global TIMER0_OVF_vect
 TIMER0_OVF_vect:
     push r16
@@ -32,3 +29,13 @@ t0_ovfl_inc:
     pop r16
 reti
 
+; shift left r22-r25 (ulong), arg in r30
+.global lsl4_r22_r30
+lsl4_r22_r30:
+    lsl r22
+    rol r23
+    rol r24
+    rol r25
+    dec r30
+    brne lsl4_r22_r30
+ret