From 6db47d6ed4fe6af8ef2cf28fc2290f21fd0b821b Mon Sep 17 00:00:00 2001
From: Brendan <2bndy5@gmail.com>
Date: Mon, 14 Aug 2023 03:06:12 -0700
Subject: [PATCH] fix #913

Essentially, this reverts the algorithm used to satisfy #650 as it has proved erroneous on fast MCUs.
---
 RF24.cpp      | 17 ++++++++---------
 RF24_config.h |  3 +++
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/RF24.cpp b/RF24.cpp
index c0cc7326..4d92aeba 100644
--- a/RF24.cpp
+++ b/RF24.cpp
@@ -1521,7 +1521,7 @@ uint8_t RF24::getDynamicPayloadSize(void)
 
 bool RF24::available(void)
 {
-    uint8_t pipe = 0;
+    uint8_t pipe = RF24_NO_FETCH_PIPE;
     return available(&pipe);
 }
 
@@ -1529,16 +1529,15 @@ bool RF24::available(void)
 
 bool RF24::available(uint8_t* pipe_num)
 {
-    // get implied RX FIFO empty flag from status byte
-    uint8_t pipe = (get_status() >> RX_P_NO) & 0x07;
-    if (pipe > 5)
-        return 0;
+    if (!isFifo(false, true)) { // if RX FIFO is not empty
+        // If the caller wants the pipe number, include that
+        if (*pipe_num != RF24_NO_FETCH_PIPE)
+            *pipe_num = (get_status() >> RX_P_NO) & 0x07;
 
-    // If the caller wants the pipe number, include that
-    if (pipe_num)
-        *pipe_num = pipe;
+        return 1;
+    }
 
-    return 1;
+    return 0;
 }
 
 /****************************************************************************/
diff --git a/RF24_config.h b/RF24_config.h
index 49b02407..2c836cab 100644
--- a/RF24_config.h
+++ b/RF24_config.h
@@ -44,6 +44,9 @@
     #define RF24_SPI_SPEED 10000000
 #endif
 
+/// A sentinel used to control fetching the pipe info in `RF24::available()`.
+#define RF24_NO_FETCH_PIPE 0XFF
+
 //ATXMega
 #if defined(__AVR_ATxmega64D3__) || defined(__AVR_ATxmega128D3__) || defined(__AVR_ATxmega192D3__) || defined(__AVR_ATxmega256D3__) || defined(__AVR_ATxmega384D3__)
     // In order to be available both in Windows and Linux this should take presence here.