From 07e49bbbd3790a95511d68b94d47bf107a5e24a1 Mon Sep 17 00:00:00 2001
From: Loek Le Blansch <loek@pipeframe.xyz>
Date: Mon, 24 Jun 2024 14:04:06 +0200
Subject: re-implement deferred I2C handlers for the Arduino pbdrv drv

---
 lib/pbdrv/drv/arduino/include.cmake |  4 +++
 lib/pbdrv/drv/arduino/index.dox     |  4 ++-
 lib/pbdrv/drv/arduino/mod.cpp       | 51 ++++++++++++++++++++++++++++---------
 3 files changed, 46 insertions(+), 13 deletions(-)

diff --git a/lib/pbdrv/drv/arduino/include.cmake b/lib/pbdrv/drv/arduino/include.cmake
index 520bfc1..5ec1124 100644
--- a/lib/pbdrv/drv/arduino/include.cmake
+++ b/lib/pbdrv/drv/arduino/include.cmake
@@ -5,3 +5,7 @@ endif()
 target_sources(pbdrv-mod PRIVATE "${CMAKE_CURRENT_LIST_DIR}/mod.cpp")
 target_link_arduino_libraries(pbdrv-mod PRIVATE core Wire)
 
+# freertos is used to defer the handling of i2c messages outside the receive
+# interrupt service routine
+include("${CMAKE_CURRENT_LIST_DIR}/../../ext/freertos/include.cmake")
+
diff --git a/lib/pbdrv/drv/arduino/index.dox b/lib/pbdrv/drv/arduino/index.dox
index 1856918..03510dd 100644
--- a/lib/pbdrv/drv/arduino/index.dox
+++ b/lib/pbdrv/drv/arduino/index.dox
@@ -10,12 +10,14 @@ This driver is known to work with the following MCUs:
 
 \par Usage
 - Link the \c pbdrv-mod library with your main executable
-- Load an \ref pb_ext "extension"
 
 \note This driver is automatically enabled if the variable \c ARDUINO is
 defined in your CMakeLists.txt (it is by default when using
 Arduino-CMake-Toolchain).
 
+\note This driver automatically includes the \ref pb_ext_freertos
+"FreeRTOS extension" for deferring calls to \c pb_i2c_recv() from the I2C ISR.
+
 A complete example for this driver is available in the \ref puzzle/dummy
 folder.
 
diff --git a/lib/pbdrv/drv/arduino/mod.cpp b/lib/pbdrv/drv/arduino/mod.cpp
index d2a6402..c381077 100644
--- a/lib/pbdrv/drv/arduino/mod.cpp
+++ b/lib/pbdrv/drv/arduino/mod.cpp
@@ -1,22 +1,33 @@
-#ifndef ARDUINO
-#error This driver only works on the Arduino platform!
-#endif
-
 #include <Arduino.h>
 #include <Wire.h>
 #include <avr/delay.h>
 
+#include <FreeRTOS.h>
+#include <timers.h>
+#include <task.h>
+
 #include "../../pb.h"
 #include "../../pb-mod.h"
 #include "../../pb-types.h"
+#include "../../pb-buf.h"
+#include "../../pb-mem.h"
+
+static void async_pb_i2c_recv(void * _msg, uint32_t _) {
+	pb_buf_t * msg = (pb_buf_t *) _msg;
+	pb_i2c_recv((uint8_t *) msg->data, msg->size);
+	pb_buf_free(msg);
+	pb_free(msg);
+}
 
 static void recv_event(int bytes) {
-	uint8_t data[bytes];
-	size_t sz = 0;
+	pb_buf_t * msg = (pb_buf_t *) pb_malloc(sizeof(pb_buf_t));
+	msg->data = (char *) pb_malloc(bytes);
+	msg->size = 0;
 	while (Wire.available())
-		data[sz++] = Wire.read();
+		msg->data[msg->size++] = Wire.read();
 
-	pb_i2c_recv(data, sz);
+	// defer pb_i2c_recv call
+	xTimerPendFunctionCallFromISR(async_pb_i2c_recv, msg, 0, NULL);
 }
 
 static void pb_setup() {
@@ -27,7 +38,17 @@ static void pb_setup() {
 	Wire.onReceive(recv_event);
 }
 
+/**
+ * \ingroup pb_drv_arduino
+ * \warning This function includes a hard-coded 10ms delay before sending. This
+ * is to work around a weird issue where the Arduino pulls both SDA and SCL low
+ * while attempting to initiate an I2C transmission. We were able to verify
+ * that the Arduino correctly handles bus arbitration under a test scenario
+ * with 2 Uno's, but ran into issues while integrating the Arduino's with the
+ * RP2040.
+ */
 __weak void pb_i2c_send(i2c_addr_t addr, const uint8_t * buf, size_t sz) {
+	vTaskDelay(10 / portTICK_PERIOD_MS); // prevent bus collisions
 	Wire.beginTransmission((int) addr);
 	Wire.write(buf, sz);
 	Wire.endTransmission(true);
@@ -41,6 +62,14 @@ extern void loop(void);
 //! Arduino internal initialization
 void init(void);
 
+//! FreeRTOS loop task
+void loop_task() {
+	for(;;) {
+		loop();
+		if (serialEventRun) serialEventRun();
+	}
+}
+
 /**
  * \ingroup pb_drv_arduino
  * \brief Application entrypoint
@@ -59,10 +88,8 @@ int main(void) {
 	init(); // call arduino internal setup
 	setup(); // call regular arduino setup
 	pb_setup(); // call pbdrv-mod setup
-	for(;;) {
-		loop();
-		if (serialEventRun) serialEventRun();
-	}
+	xTaskCreate((TaskFunction_t) loop_task, "loop", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY + 1, NULL);
+	vTaskStartScheduler(); // start freertos scheduler
 	return 0;
 }
 
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