Disable RS485 driver and systick before deep sleep

- The RS485 driver consumes about 150 mW if enabled
- The systick somehow can wake up the CPU from stop mode

src/main.c

@@ -15,6 +15,7 @@
 #include "measurement.h"
 #include "deepsleep.h"
 
+#include "pinout.h"
 #include "config.h"
 
 volatile int wait_frame = 1;
@@ -223,8 +224,13 @@ int main(void)
 				} else {
 					// charge control already idle
 					if((timebase_ms - charge_control_idle_since) > DEEPSLEEP_DELAY) {
-						rs485_enqueue("PWR:DEEPSLEEP:ENTRY\n");
+						systick_counter_disable();
+						// force the RS485 driver into receive mode. The RS485
+						// driver alone consumes 150 mW if enabled.
+						gpio_clear(RS485_PORT, RS485_DE_PIN);
 						deepsleep(DEEPSLEEP_DURATION);
+						gpio_set(RS485_PORT, RS485_DE_PIN);
+						systick_counter_enable();
 						rs485_enqueue("PWR:DEEPSLEEP:EXIT\n");
 						charge_control_was_idle = false;
 					}