altos/stmf0: Have fast ADC ring buffer code use wrap-around

[fw/altos] / src / stmf0 / ao_adc_fast.h

diff --git a/src/stmf0/ao_adc_fast.h b/src/stmf0/ao_adc_fast.h
index ca5f7fb9fc5a9d5ed864f3990b533adb25e9be90..c6903e9fcccb3b1d618eb29793bf861e87d6f659 100644 (file)
--- a/src/stmf0/ao_adc_fast.h
+++ b/src/stmf0/ao_adc_fast.h
@@ -31,52 +31,53 @@ extern uint16_t     ao_adc_ring[AO_ADC_RING_SIZE];
 
 #define ao_adc_ring_step(pos,inc)      (((pos) + (inc)) & (AO_ADC_RING_SIZE - 1))
 
-extern uint16_t        ao_adc_ring_head, ao_adc_ring_tail;
+extern uint16_t        ao_adc_ring_head, ao_adc_ring_remain;
 extern uint16_t        ao_adc_running;
 
-void
-_ao_adc_start(void);
-
+/*
+ * Place to start fetching values from
+ */
 static inline uint16_t
-_ao_adc_remain(void)
+ao_adc_ring_tail(void)
 {
-       if (ao_adc_ring_tail > ao_adc_ring_head)
-               return AO_ADC_RING_SIZE - ao_adc_ring_tail;
-       return ao_adc_ring_head - ao_adc_ring_tail;
+       return (ao_adc_ring_head - ao_adc_ring_remain) & (AO_ADC_RING_SIZE - 1);
 }
 
+void
+_ao_adc_start(void);
+
+/*
+ * Space available to write ADC values into
+ */
 static inline uint16_t
 _ao_adc_space(void)
 {
-       if (ao_adc_ring_head >= ao_adc_ring_tail)
+       /* Free to end of buffer? */
+       if (ao_adc_ring_remain <= ao_adc_ring_head)
                return AO_ADC_RING_SIZE - ao_adc_ring_head;
-       return ao_adc_ring_tail - ao_adc_ring_head;
+
+       /* no, return just the unused entries beyond head */
+       return AO_ADC_RING_SIZE - ao_adc_ring_remain;
 }
 
-static inline uint16_t *
+static inline uint16_t
 ao_adc_get(uint16_t n)
 {
-       if (ao_adc_ring_tail + n > AO_ADC_RING_SIZE)
-               ao_panic(AO_PANIC_ADC);
        ao_arch_block_interrupts();
-       while (_ao_adc_remain() < n) {
+       while (ao_adc_ring_remain < n) {
                if (!ao_adc_running)
                        _ao_adc_start();
                ao_sleep(&ao_adc_ring_head);
        }
        ao_arch_release_interrupts();
-       return &ao_adc_ring[ao_adc_ring_tail];
+       return ao_adc_ring_tail();
 }
 
 static inline void
 ao_adc_ack(uint16_t n)
 {
-       if (ao_adc_ring_tail + n > AO_ADC_RING_SIZE)
-               ao_panic(AO_PANIC_ADC);
        ao_arch_block_interrupts();
-       ao_adc_ring_tail += n;
-       if (ao_adc_ring_tail == AO_ADC_RING_SIZE)
-               ao_adc_ring_tail = 0;
+       ao_adc_ring_remain -= n;
        if (!ao_adc_running)
                _ao_adc_start();
        ao_arch_release_interrupts();