diff options
| -rw-r--r-- | Makefile | 4 | ||||
| -rw-r--r-- | main.c | 36 |
2 files changed, 13 insertions, 27 deletions
@@ -10,8 +10,8 @@ CFLAGS += -mmcu=attiny2313a -DF_CPU=20000000UL #CFLAGS += -gdwarf-2 -fverbose-asm CFLAGS += -I. -std=gnu99 -Os -Wall -Wextra -pedantic CFLAGS += -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -# r28 .. r31 hold the microsecond counters -CFLAGS += -ffixed-28 -ffixed-29 -ffixed-30 -ffixed-31 +# r28 / r29 hold the microsecond counters +CFLAGS += -ffixed-28 -ffixed-29 CFLAGS += -fwhole-program -flto -mstrict-X AVRFLAGS += -U lfuse:w:0xe4:m -U hfuse:w:0xdf:m -U efuse:w:0xff:m @@ -46,23 +46,21 @@ * otherwise during the main loop), all program variables are saved in * registers. * - * The HCNT / LCNT registers count how many microseconds have passed + * The LCNT registers count how many microseconds have passed * since the last low-to-high / high-to-low transition. In the main loop, - * only r28 .. r31 (Y and Z) are incremented (precisely once per microsecond), + * only r28 and r29 (Y) are incremented (precisely once per microsecond), * their GPIO counterparts are used in the ISR and synced with the registers * both at start and end. * * Note: The compiler knows that these registers are forbiden thanks to - * -ffixed-28 ... -ffixed-31 + * -ffixed-28 -ffixed-29 * - * HCNT = r30 (ZL), r31 (ZH) * LCNT = r28 (YL), r29 (YH) */ #define LCNTH GPIOR2 #define LCNTL GPIOR1 -#define HCNTL GPIOR0 #define CNT USIDR #define LASTCMD OCR0B @@ -82,16 +80,6 @@ asm volatile ("cp r28, r1"); \ asm volatile ("brne .-12"); -#define delay_us_Z(delay) \ - asm volatile ("ldi r31, 0"); \ - asm volatile ("ldi r30, %0" : : "M" (delay)); \ - asm volatile ("wdr"); \ - asm volatile ("wdr"); \ - asm volatile ("wdr"); \ - asm volatile ("sbiw r30, 1"); \ - asm volatile ("cp r30, r1"); \ - asm volatile ("brne .-12"); - int main (void) { /* watchdog reset after ~4 seconds - just in case */ @@ -119,20 +107,18 @@ int main (void) asm volatile ("ldi r28, 0"); asm volatile ("ldi r29, 0"); - asm volatile ("ldi r30, 0"); - asm volatile ("ldi r31, 0"); /* * takes exactly 1us per cycle */ loop: - asm volatile ("inc r30"); // 1c asm volatile ("adiw r28, 1"); // 2c asm volatile ("wdr"); // 1c asm volatile ("nop"); // 1c asm volatile ("nop"); // 1c asm volatile ("nop"); // 1c - goto loop; + asm volatile ("nop"); // 1c + goto loop; // 1c return 0; } @@ -143,11 +129,10 @@ ISR(INT1_vect) if (PIND & _BV(PD3)) { /* - * Make LCNT / HCNT available to the C compiler + * Make LCNT available to the C compiler */ asm volatile ("out %0, r29" : : "M" (_SFR_IO_ADDR(LCNTH))); asm volatile ("out %0, r28" : : "M" (_SFR_IO_ADDR(LCNTL))); - asm volatile ("out %0, r30" : : "M" (_SFR_IO_ADDR(HCNTL))); /* * Line was high for >256us - got reset signal, send presence @@ -155,7 +140,11 @@ ISR(INT1_vect) if (LCNTH > 0) { DDRD = _BV(PD3); - delay_us_Z(120); + /* + * Y register is no longer needed at this point and may be + * overwritten. + */ + delay_us_Y(120); DDRD = 0; LASTCMD = 0; @@ -193,9 +182,6 @@ ISR(INT1_vect) EEAR = 0; EIFR |= _BV(INTF1); } - - - asm volatile ("ldi r30, 1"); // HCNTL = 1 } else { if (LASTCMD == 0x33) { |