HAL_ChibiOS: disable shared DMA on IOMCU

this saves about 600 bytes of ram

libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp

@@ -192,7 +192,10 @@ static void main_loop()
     ChibiOS::I2CBus::clear_all();
 #endif
 
+#ifndef HAL_NO_SHARED_DMA
     ChibiOS::Shared_DMA::init();
+#endif
+
     peripheral_power_enable();
 
     hal.serial(0)->begin(115200);

libraries/AP_HAL_ChibiOS/RCOutput.cpp

@@ -154,6 +154,7 @@ void RCOutput::rcout_thread()
     }
 }
 
+#ifndef HAL_NO_SHARED_DMA
 // release locks on the groups that are pending in reverse order
 void RCOutput::dshot_collect_dma_locks(uint32_t last_run_us)
 {
@@ -192,6 +193,7 @@ void RCOutput::dshot_collect_dma_locks(uint32_t last_run_us)
         }
     }
 }
+#endif // HAL_NO_SHARED_DMA
 
 /*
   setup the output frequency for a group and start pwm output

libraries/AP_HAL_ChibiOS/Util.cpp

@@ -375,7 +375,9 @@ void Util::thread_info(ExpandingString &str)
 // request information on dma contention
 void Util::dma_info(ExpandingString &str)
 {
+#ifndef HAL_NO_SHARED_DMA
     ChibiOS::Shared_DMA::dma_info(str);
+#endif
 }
 #endif
 

libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c

@@ -276,7 +276,6 @@ void set_rtc_backup(uint8_t idx, const uint32_t *v, uint8_t n)
 // get RTC backup registers starting at given idx
 void get_rtc_backup(uint8_t idx, uint32_t *v, uint8_t n)
 {
-    return 0;
 }
 #endif // NO_FASTBOOT
 

libraries/AP_HAL_ChibiOS/hwdef/iomcu/hwdef.dat

@@ -120,6 +120,7 @@ define HAL_NO_TIMER_THREAD
 define HAL_NO_RCIN_THREAD
 define HAL_NO_MONITOR_THREAD
 define HAL_NO_RCOUT_THREAD
+define HAL_NO_SHARED_DMA
 
 #defined to turn off undef warnings
 define __FPU_PRESENT 0

libraries/AP_HAL_ChibiOS/shared_dma.cpp

@@ -20,7 +20,7 @@
   code to handle sharing of DMA channels between peripherals
  */
 
-#if CH_CFG_USE_MUTEXES == TRUE
+#if CH_CFG_USE_MUTEXES == TRUE && !defined(HAL_NO_SHARED_DMA)
 
 #include <AP_Common/ExpandingString.h>
 
@@ -267,3 +267,4 @@ void Shared_DMA::dma_info(ExpandingString &str)
 }
 
 #endif // CH_CFG_USE_SEMAPHORES
+

libraries/AP_HAL_ChibiOS/shared_dma.h

@@ -23,6 +23,8 @@
 // DMA stream ID for stream_id2 when only one is needed
 #define SHARED_DMA_NONE 255
 
+#ifndef HAL_NO_SHARED_DMA
+
 class ChibiOS::Shared_DMA
 {
 public:
@@ -108,3 +110,5 @@ private:
         uint32_t transactions;
     } *_contention_stats;
 };
+
+#endif // HAL_NO_SHARED_DMA