Use a fixed transaction buffer size

main/i2c.cpp

@@ -1,16 +1,22 @@
 #include "i2c.hpp"
+#include <cstdint>
 
 #include "assert.h"
+#include "driver/i2c.h"
 
 namespace gay_ipod {
 
 I2CTransaction::I2CTransaction() {
-  handle_ = i2c_cmd_link_create();
+  // Use a fixed size buffer to avoid many many tiny allocations.
+  // TODO: make this static and tune the size. possibly make it optional too?
+  // threading.
+  buffer_ = (uint8_t*) calloc(sizeof(uint8_t), I2C_LINK_RECOMMENDED_SIZE(10));
+  handle_ = i2c_cmd_link_create_static(buffer_, I2C_LINK_RECOMMENDED_SIZE(10));
   assert(handle_ != NULL && "failed to create command link");
 }
 
 I2CTransaction::~I2CTransaction() {
-  i2c_cmd_link_delete(handle_);
+  free(buffer_);
 }
 
 esp_err_t I2CTransaction::Execute() {

main/i2c.hpp

@@ -78,6 +78,7 @@ class I2CTransaction {
 
  private:
   i2c_cmd_handle_t handle_;
+  uint8_t *buffer_;
 };
 
 }  // namespace gay_ipod