Protect the HW random generation from FreeRTOS (#1395)

Fixes #1394

The Pico_Rand SDK calls gather bits from the HW ROSC at precise intervals.
If there is jitter in the sleep_until() call then the ROSC bit collection
will always think it's failed to acquire the right bit and retry infintitely.

Avoid by wrapping the HW random number calls and the sleep_until() routine.
Only when in FreeRTOS set a flag to silently make sleep_until() into a
busy wait loop while in a random number generation step.  When not in the
random code, do the normal sleep_until call.

Author: earlephilhower

cores/rp2040/_freertos.cpp

@@ -21,6 +21,7 @@
 #include "_freertos.h"
 #include "pico/mutex.h"
 #include <stdlib.h>
+#include "Arduino.h"
 
 typedef struct {
     mutex_t *src;
@@ -59,3 +60,45 @@ SemaphoreHandle_t __get_freertos_mutex_for_ptr(mutex_t *m, bool recursive) {
     }
     return nullptr; // Need to make space for more mutex maps!
 }
+
+
+// The HW Random code needs a precise sleep_until() in order to assure it
+// grabs the ROSC bit when it wants.  Unfortunately, under FreeRTOS the
+// sleep_until() becomes imprecise and the "did I get the bit when I wanted"
+// check in the pico_rand code always fails and you get an infinite loop.
+
+// This block wraps the 2 get_rand calls to set a flag to convert
+// sleep_until() (which can do a task swap and cause bad timing) into a
+// busy wait.
+
+extern "C" {
+    static bool __inRand = false;
+
+    extern uint64_t __real_get_rand_64();
+    uint64_t __wrap_get_rand_64() {
+        if (__isFreeRTOS) {
+            rp2040.idleOtherCore();
+            __inRand = true;
+            auto r = __real_get_rand_64();
+            __inRand = false;
+            rp2040.resumeOtherCore();
+            return r;
+        } else {
+            return __real_get_rand_64();
+        }
+    }
+
+    uint32_t __wrap_get_rand_32() {
+        return (uint32_t) __wrap_get_rand_64();
+    }
+
+    extern void __real_sleep_until(absolute_time_t t);
+    void __wrap_sleep_until(absolute_time_t t) {
+        if (__inRand) {
+            busy_wait_until(t);
+        } else {
+            __real_sleep_until(t);
+        }
+    }
+
+}

lib/platform_wrap.txt

@@ -207,3 +207,7 @@
 -Wl,--wrap=cyw43_tcpip_link_status
 -Wl,--wrap=cyw43_cb_tcpip_init
 -Wl,--wrap=cyw43_cb_tcpip_deinit
+
+-Wl,--wrap=get_rand_64
+-Wl,--wrap=get_rand_32
+-Wl,--wrap=sleep_until

tests/restyle.sh

@@ -10,7 +10,7 @@ for dir in ./cores/rp2040 ./libraries/EEPROM ./libraries/I2S ./libraries/SingleF
            ./libraries/Updater ./libraries/HTTPClient ./libraries/HTTPUpdate \
            ./libraries/WebServer ./libraries/HTTPUpdateServer ./libraries/DNSServer \
            ./libraries/Joystick ./libraries/Keyboard ./libraries/Mouse \
-           ./libraries/JoystickBT ./libraries/KeyboardBT ./variants ./libraries/BTstack \
+           ./libraries/JoystickBT ./libraries/KeyboardBT ./variants ./libraries/BTstackLib \
            ./libraries/MouseBT ./libraries/SerialBT ./libraries/HID_Bluetooth \
            ./libraries/JoystickBLE ./libraries/KeyboardBLE ./libraries/MouseBLE ; do
     find $dir -type f \( -name "*.c" -o -name "*.h" -o -name "*.cpp" \) -a  \! -path '*api*' -exec astyle --suffix=none --options=./tests/astyle_core.conf \{\} \;