Shared irq line, guard shared IRQ line against hangs/timeouts

src/st25r3916_interrupt.cpp

@@ -48,6 +48,21 @@
 /*! Length of the interrupt registers       */
 #define ST25R3916_INT_REGS_LEN          ( (ST25R3916_REG_IRQ_TARGET - ST25R3916_REG_IRQ_MAIN) + 1U )
 
+#ifdef ST25R3916_SHARED_IRQ_LINE
+  /*! Upper bound on IRQ-register reads per st25r3916Isr() call.  Only reached
+  *  when another device on the shared IRQ line is holding it asserted, which
+  *  this IC cannot clear.  Rationale in st25r3916CheckForReceivedInterrupts(). */
+  #ifndef ST25R3916_ISR_MAX_REG_READS
+    #define ST25R3916_ISR_MAX_REG_READS     8U
+  #endif
+
+  /*! Interval at which st25r3916WaitForInterruptsTimed() polls the IRQ registers
+  *  instead of trusting a pin edge to have filled in the interrupt status. */
+  #ifndef ST25R3916_IRQ_POLL_INTERVAL_US
+    #define ST25R3916_IRQ_POLL_INTERVAL_US  200U
+  #endif
+#endif /* ST25R3916_SHARED_IRQ_LINE */
+
 /*
  ******************************************************************************
  * LOCAL DATA TYPES
@@ -99,6 +114,34 @@ void RfalRfST25R3916Class::st25r3916CheckForReceivedInterrupts(void)
   ST_MEMSET(iregs, (int32_t)(ST25R3916_IRQ_MASK_ALL & 0xFFU), ST25R3916_INT_REGS_LEN);
 
 
+#ifdef ST25R3916_SHARED_IRQ_LINE
+  /* Read this IC's IRQ registers at least once, then repeat while the pin is
+   * still asserted, up to a bounded number of reads.
+   *
+   * The default path below uses the pin level as the sole entry condition, which
+   * assumes the pin belongs to exactly one IC.  When the line is shared, its
+   * level describes the bus rather than the selected IC, and it fails in both
+   * directions: held de-asserted, nothing is ever collected and every wait times
+   * out; held asserted by another IC, the while() cannot terminate because this
+   * IC has nothing left to clear.  Reading unconditionally makes collection
+   * depend on the IC rather than on the wire, and the bound makes a foreign
+   * assertion cost a fixed number of SPI transactions instead of hanging.
+   *
+   * Undefine ST25R3916_SHARED_IRQ_LINE to get the upstream behaviour back; that
+   * is the correct choice as soon as the pin can represent per-IC state, i.e.
+   * one IRQ line per IC, or a true wired-OR of active-high outputs. */
+  uint8_t reads = 0U;
+  do {
+    st25r3916ReadMultipleRegisters(ST25R3916_REG_IRQ_MAIN, iregs, ST25R3916_INT_REGS_LEN);
+
+    irqStatus |= (uint32_t)iregs[0];
+    irqStatus |= (uint32_t)iregs[1] << 8;
+    irqStatus |= (uint32_t)iregs[2] << 16;
+    irqStatus |= (uint32_t)iregs[3] << 24;
+
+    reads++;
+  } while ((digitalRead(int_pin) == HIGH) && (reads < ST25R3916_ISR_MAX_REG_READS));
+#else
   /* In case the IRQ is Edge (not Level) triggered read IRQs until done */
   while (digitalRead(int_pin) == HIGH) {
     st25r3916ReadMultipleRegisters(ST25R3916_REG_IRQ_MAIN, iregs, ST25R3916_INT_REGS_LEN);
@@ -108,6 +151,7 @@ void RfalRfST25R3916Class::st25r3916CheckForReceivedInterrupts(void)
     irqStatus |= (uint32_t)iregs[2] << 16;
     irqStatus |= (uint32_t)iregs[3] << 24;
   }
+#endif /* ST25R3916_SHARED_IRQ_LINE */
 
   /* Forward all interrupts, even masked ones to application */
   st25r3916interrupt.status |= irqStatus;
@@ -146,10 +190,36 @@ uint32_t RfalRfST25R3916Class::st25r3916WaitForInterruptsTimed(uint32_t mask, ui
 
   tmrDelay = timerCalculateTimer(tmo);
 
+#ifdef ST25R3916_SHARED_IRQ_LINE
+  /* Poll this IC's IRQ registers while waiting, rather than only spinning on
+   * st25r3916interrupt.status.
+   *
+   * The default path below assumes a pin-edge ISR is filling in .status
+   * concurrently.  On a shared IRQ line that edge is not dependable (see
+   * st25r3916CheckForReceivedInterrupts()), so .status can stay empty and the
+   * loop always runs to its timeout -- which is every transceive.  Calling
+   * st25r3916CheckForReceivedInterrupts() on an interval fetches this IC's
+   * own registers over SPI, so progress no longer depends on the pin.
+   *
+   * Timing uses micros() rather than the RFAL timer, since timerIsExpired() is
+   * the coarse ms timer being used for the outer bound.  The unsigned delta is
+   * wraparound-safe at this interval. */
+  uint32_t last_us = micros();
+
+  do {
+    uint32_t now_us = micros();
+    if ((now_us - last_us) >= ST25R3916_IRQ_POLL_INTERVAL_US) {
+      st25r3916CheckForReceivedInterrupts();
+      last_us = now_us;
+    }
+    status = (st25r3916interrupt.status & mask);
+  } while ((!timerIsExpired(tmrDelay) || (tmo == 0U)) && (status == 0U));
+#else
   /* Run until specific interrupt has happen or the timer has expired */
   do {
     status = (st25r3916interrupt.status & mask);
   } while ((!timerIsExpired(tmrDelay) || (tmo == 0U)) && (status == 0U));
+#endif /* ST25R3916_SHARED_IRQ_LINE */
 
   status = st25r3916interrupt.status & mask;