BSRAM progmem. fix Makefile memory command that does not work. add interrupts, bank 1, timer0. Timer0 not tested.

1 files changed, 53 insertions, 0 deletions

diff --git a/fw/pwm.c b/fw/pwm.c
new file mode 100644
index 0000000..60f8b5c
--- /dev/null
+++ b/fw/pwm.c
@@ -0,0 +1,53 @@
+#include <pic16f84a.h>
+
+typedef unsigned char uint8_t;
+
+/*
+ * Breathing LED via bit-bang PWM on PORTA(0) and PORTB(0).
+ *
+ * The PWM period is 256 counts of the inner counter 'pwm'.
+ * Each duty level is held for HOLD_PERIODS full PWM periods before
+ * stepping, giving a smooth fade up then down (heartbeat pattern).
+ *
+ * At 50 MHz with SDCC's output (~10 instructions/iteration) the inner
+ * loop runs at roughly 5 MHz, so one 256-count PWM period ≈ 51 µs
+ * → ~20 kHz PWM.  With HOLD_PERIODS = 32 each brightness step lasts
+ * ~1.6 ms and the full 0→255→0 sweep takes ~820 ms — a natural breath.
+ * Tweak HOLD_PERIODS to taste.
+ */
+
+#define HOLD_PERIODS 32
+
+void main(void) {
+    uint8_t duty    = 0;   /* current duty cycle, 0..255              */
+    uint8_t dir     = 1;   /* 1 = ramping up, 0 = ramping down        */
+    uint8_t pwm     = 0;   /* free-running counter within one period  */
+    uint8_t periods = 0;   /* how many full periods at this duty level */
+
+    while (1) {
+        /* PWM compare: LED on when we're inside the duty window */
+        if (pwm < duty) {
+            PORTA = 0x01;
+            PORTB = 0x01;
+        } else {
+            PORTA = 0x00;
+            PORTB = 0x00;
+        }
+
+        pwm++;  /* wraps 255→0, completing one 256-count PWM period */
+
+        if (pwm == 0) {
+            periods++;
+            if (periods == HOLD_PERIODS) {
+                periods = 0;
+                if (dir) {
+                    duty++;
+                    if (duty == 255) dir = 0;   /* peak: start ramping down */
+                } else {
+                    duty--;
+                    if (duty == 0)   dir = 1;   /* floor: start ramping up  */
+                }
+            }
+        }
+    }
+}