HAL_ChibiOS: allow for bare board builds

this allows for a build with no UARTs, no SPI, no I2C, no PWM. Great
for initial board bringup with just USB

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -186,6 +186,7 @@ void UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
         }
 #endif
     } else {
+#if HAL_USE_SERIAL == TRUE
         if (_baudrate != 0) {
             bool was_initialised = _device_initialised;            
             //setup Rx DMA
@@ -248,6 +249,7 @@ void UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
                 }
             }
         }
+#endif // HAL_USE_SERIAL
     }
 
     if (_writebuf.get_size() && _readbuf.get_size()) {
@@ -261,6 +263,7 @@ void UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
 
 void UARTDriver::dma_tx_allocate(void)
 {
+#if HAL_USE_SERIAL == TRUE
     osalDbgAssert(txdma == nullptr, "double DMA allocation");
     txdma = STM32_DMA_STREAM(sdef.dma_tx_stream_id);
     chSysLock();
@@ -271,6 +274,7 @@ void UARTDriver::dma_tx_allocate(void)
     osalDbgAssert(!dma_allocated, "stream already allocated");
     chSysUnlock();
     dmaStreamSetPeripheral(txdma, &((SerialDriver*)sdef.serial)->usart->DR);
+#endif // HAL_USE_SERIAL
 }
 
 void UARTDriver::dma_tx_deallocate(void)
@@ -303,6 +307,7 @@ void UARTDriver::tx_complete(void* self, uint32_t flags)
 
 void UARTDriver::rx_irq_cb(void* self)
 {
+#if HAL_USE_SERIAL == TRUE
     UARTDriver* uart_drv = (UARTDriver*)self;
     if (!uart_drv->sdef.dma_rx) {
         return;
@@ -314,10 +319,12 @@ void UARTDriver::rx_irq_cb(void* self)
         //disable dma, triggering DMA transfer complete interrupt
         uart_drv->rxdma->stream->CR &= ~STM32_DMA_CR_EN;
     }
+#endif // HAL_USE_SERIAL
 }
 
 void UARTDriver::rxbuff_full_irq(void* self, uint32_t flags)
 {
+#if HAL_USE_SERIAL == TRUE
     UARTDriver* uart_drv = (UARTDriver*)self;
     if (uart_drv->_lock_rx_in_timer_tick) {
         return;
@@ -342,6 +349,7 @@ void UARTDriver::rxbuff_full_irq(void* self, uint32_t flags)
     if (uart_drv->_rts_is_active) {
         uart_drv->update_rts_line();
     }
+#endif // HAL_USE_SERIAL
 }
 
 void UARTDriver::begin(uint32_t b)
@@ -360,7 +368,9 @@ void UARTDriver::end()
         sduStop((SerialUSBDriver*)sdef.serial);
 #endif
     } else {
+#if HAL_USE_SERIAL == TRUE
         sdStop((SerialDriver*)sdef.serial);
+#endif
     }
     _readbuf.set_size(0);
     _writebuf.set_size(0);
@@ -558,14 +568,16 @@ void UARTDriver::write_pending_bytes_NODMA(uint32_t n)
     ByteBuffer::IoVec vec[2];
     const auto n_vec = _writebuf.peekiovec(vec, n);
     for (int i = 0; i < n_vec; i++) {
-        int ret;
+        int ret = -1;
         if (sdef.is_usb) {
             ret = 0;
 #ifdef HAVE_USB_SERIAL
             ret = chnWriteTimeout((SerialUSBDriver*)sdef.serial, vec[i].data, vec[i].len, TIME_IMMEDIATE);
 #endif
         } else {
+#if HAL_USE_SERIAL == TRUE
             ret = chnWriteTimeout((SerialDriver*)sdef.serial, vec[i].data, vec[i].len, TIME_IMMEDIATE);
+#endif
         }
         if (ret < 0) {
             break;
@@ -682,7 +694,9 @@ void UARTDriver::_timer_tick(void)
     #endif
             } else {
                 ret = 0;
+#if HAL_USE_SERIAL == TRUE
                 ret = chnReadTimeout((SerialDriver*)sdef.serial, vec[i].data, vec[i].len, TIME_IMMEDIATE);
+#endif
             }
             if (ret < 0) {
                 break;
@@ -721,7 +735,7 @@ void UARTDriver::set_flow_control(enum flow_control flowcontrol)
         // no hw flow control available
         return;
     }
-
+#if HAL_USE_SERIAL == TRUE
     _flow_control = flowcontrol;
     if (!_initialised) {
         // not ready yet, we just set variable for when we call begin
@@ -755,6 +769,7 @@ void UARTDriver::set_flow_control(enum flow_control flowcontrol)
         ((SerialDriver*)(sdef.serial))->usart->CR3 &= ~USART_CR3_RTSE;
         break;
     }
+#endif // HAL_USE_SERIAL
 }
 
 /*
@@ -798,6 +813,7 @@ void UARTDriver::configure_parity(uint8_t v)
         // not possible
         return;
     }
+#if HAL_USE_SERIAL == TRUE
     // stop and start to take effect
     sdStop((SerialDriver*)sdef.serial);
     
@@ -826,6 +842,7 @@ void UARTDriver::configure_parity(uint8_t v)
         //because we will handle them via DMA
         ((SerialDriver*)sdef.serial)->usart->CR1 &= ~USART_CR1_RXNEIE;
     }
+#endif // HAL_USE_SERIAL
 }
 
 /*
@@ -837,6 +854,7 @@ void UARTDriver::set_stop_bits(int n)
         // not possible
         return;
     }
+#if HAL_USE_SERIAL
     // stop and start to take effect
     sdStop((SerialDriver*)sdef.serial);
     
@@ -854,6 +872,7 @@ void UARTDriver::set_stop_bits(int n)
         //because we will handle them via DMA
         ((SerialDriver*)sdef.serial)->usart->CR1 &= ~USART_CR1_RXNEIE;
     }
+#endif // HAL_USE_SERIAL
 }