machine: make UART objects pointer receivers

This means that machine.UART0, machine.UART1, etc are of type
*machine.UART, not machine.UART. This makes them easier to pass around
and avoids surprises when they are passed around by value while they
should be passed around by reference.

There is a small code size impact in some cases, but it is relatively
minor.

45 files changed, 242 insertions, 175 deletions

diff --git a/src/machine/board_arduino_nano33_baremetal.go b/src/machine/board_arduino_nano33_baremetal.go
index 584f65ee2..79e62d243 100644
--- a/src/machine/board_arduino_nano33_baremetal.go
+++ b/src/machine/board_arduino_nano33_baremetal.go
@@ -9,7 +9,8 @@ import (
 
 // UART1 on the Arduino Nano 33 connects to the onboard NINA-W102 WiFi chip.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM3_USART,
 		SERCOM: 3,
@@ -18,7 +19,8 @@ var (
 
 // UART2 on the Arduino Nano 33 connects to the normal TX/RX pins.
 var (
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM5_USART,
 		SERCOM: 5,
@@ -26,8 +28,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5, _UART2.handleInterrupt)
 }
 
 // I2C on the Arduino Nano 33.
diff --git a/src/machine/board_atsame54-xpro.go b/src/machine/board_atsame54-xpro.go
index d5d1f6819..a70ab7b0f 100644
--- a/src/machine/board_atsame54-xpro.go
+++ b/src/machine/board_atsame54-xpro.go
@@ -240,28 +240,32 @@ var (
 // UART on the SAM E54 Xplained Pro
 var (
 	// Extension Header EXT1
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
 	}
 
 	// Extension Header EXT2
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM5_USART_INT,
 		SERCOM: 5,
 	}
 
 	// Extension Header EXT3
-	UART3 = UART{
+	UART3  = &_UART3
+	_UART3 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM1_USART_INT,
 		SERCOM: 1,
 	}
 
 	// EDBG Virtual COM Port
-	UART4 = UART{
+	UART4  = &_UART4
+	_UART4 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM2_USART_INT,
 		SERCOM: 2,
@@ -269,10 +273,10 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, UART2.handleInterrupt)
-	UART3.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, UART3.handleInterrupt)
-	UART4.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, UART4.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART2.handleInterrupt)
+	UART3.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, _UART3.handleInterrupt)
+	UART4.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, _UART4.handleInterrupt)
 }
 
 // I2C on the SAM E54 Xplained Pro
diff --git a/src/machine/board_bluepill.go b/src/machine/board_bluepill.go
index 51e389349..4aece086e 100644
--- a/src/machine/board_bluepill.go
+++ b/src/machine/board_bluepill.go
@@ -61,19 +61,21 @@ const (
 var (
 	// USART1 is the first hardware serial port on the STM32.
 	// Both UART0 and UART1 refer to USART1.
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    stm32.USART1,
 	}
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    stm32.USART2,
 	}
 )
 
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART1, UART0.handleInterrupt)
-	UART1.Interrupt = interrupt.New(stm32.IRQ_USART2, UART1.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART1, _UART0.handleInterrupt)
+	UART1.Interrupt = interrupt.New(stm32.IRQ_USART2, _UART1.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_circuitplay_express_baremetal.go b/src/machine/board_circuitplay_express_baremetal.go
index 78709baa9..f99043e17 100644
--- a/src/machine/board_circuitplay_express_baremetal.go
+++ b/src/machine/board_circuitplay_express_baremetal.go
@@ -9,7 +9,8 @@ import (
 
 // UART1 on the Circuit Playground Express.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM4_USART,
 		SERCOM: 4,
@@ -17,7 +18,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, _UART1.handleInterrupt)
 }
 
 // I2C on the Circuit Playground Express.
diff --git a/src/machine/board_feather-m0.go b/src/machine/board_feather-m0.go
index 4c7f664ee..f0f72ea75 100644
--- a/src/machine/board_feather-m0.go
+++ b/src/machine/board_feather-m0.go
@@ -56,7 +56,8 @@ const (
 
 // UART1 on the Feather M0.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM1_USART,
 		SERCOM: 1,
@@ -64,7 +65,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, _UART1.handleInterrupt)
 }
 
 // I2C pins
diff --git a/src/machine/board_feather-m4-can.go b/src/machine/board_feather-m4-can.go
index 795a6a3e2..5ad3cd156 100644
--- a/src/machine/board_feather-m4-can.go
+++ b/src/machine/board_feather-m4-can.go
@@ -103,13 +103,15 @@ var (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM5_USART_INT,
 		SERCOM: 5,
 	}
 
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
@@ -117,8 +119,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
 
 	// turn on neopixel
 	D7.Configure(PinConfig{Mode: PinOutput})
diff --git a/src/machine/board_feather-m4_baremetal.go b/src/machine/board_feather-m4_baremetal.go
index bfe47ecf0..d0d9d6dd6 100644
--- a/src/machine/board_feather-m4_baremetal.go
+++ b/src/machine/board_feather-m4_baremetal.go
@@ -8,13 +8,15 @@ import (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM5_USART_INT,
 		SERCOM: 5,
 	}
 
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
@@ -22,8 +24,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
 }
 
 // I2C on the Feather M4.
diff --git a/src/machine/board_feather-stm32f405.go b/src/machine/board_feather-stm32f405.go
index 17d8b93f9..f55572ff0 100644
--- a/src/machine/board_feather-stm32f405.go
+++ b/src/machine/board_feather-stm32f405.go
@@ -119,19 +119,22 @@ const (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART3,
 		TxAltFuncSelector: AF7_USART1_2_3,
 		RxAltFuncSelector: AF7_USART1_2_3,
 	}
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART6,
 		TxAltFuncSelector: AF8_USART4_5_6,
 		RxAltFuncSelector: AF8_USART4_5_6,
 	}
-	UART3 = UART{
+	UART3  = &_UART3
+	_UART3 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART1,
 		TxAltFuncSelector: AF7_USART1_2_3,
@@ -141,9 +144,9 @@ var (
 )
 
 func initUART() {
-	UART1.Interrupt = interrupt.New(stm32.IRQ_USART3, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(stm32.IRQ_USART6, UART2.handleInterrupt)
-	UART3.Interrupt = interrupt.New(stm32.IRQ_USART1, UART3.handleInterrupt)
+	UART1.Interrupt = interrupt.New(stm32.IRQ_USART3, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(stm32.IRQ_USART6, _UART2.handleInterrupt)
+	UART3.Interrupt = interrupt.New(stm32.IRQ_USART1, _UART3.handleInterrupt)
 }
 
 // -- SPI ----------------------------------------------------------------------
diff --git a/src/machine/board_grandcentral-m4_baremetal.go b/src/machine/board_grandcentral-m4_baremetal.go
index 74f0a39d6..a59bd95bf 100644
--- a/src/machine/board_grandcentral-m4_baremetal.go
+++ b/src/machine/board_grandcentral-m4_baremetal.go
@@ -8,30 +8,34 @@ import (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, UART2.handleInterrupt)
-	UART3.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, UART3.handleInterrupt)
-	UART4.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, UART4.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, _UART2.handleInterrupt)
+	UART3.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, _UART3.handleInterrupt)
+	UART4.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART4.handleInterrupt)
 }
 
 // UART on the Grand Central M4
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
 	}
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM4_USART_INT,
 		SERCOM: 4,
 	}
-	UART3 = UART{
+	UART3  = &_UART3
+	_UART3 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM1_USART_INT,
 		SERCOM: 1,
 	}
-	UART4 = UART{
+	UART4  = &_UART4
+	_UART4 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM5_USART_INT,
 		SERCOM: 5,
diff --git a/src/machine/board_itsybitsy-m0.go b/src/machine/board_itsybitsy-m0.go
index 189557aee..a4161429c 100644
--- a/src/machine/board_itsybitsy-m0.go
+++ b/src/machine/board_itsybitsy-m0.go
@@ -56,7 +56,8 @@ const (
 
 // UART1 on the ItsyBitsy M0.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM1_USART,
 		SERCOM: 1,
@@ -64,7 +65,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, _UART1.handleInterrupt)
 }
 
 // I2C pins
diff --git a/src/machine/board_itsybitsy-m4_baremetal.go b/src/machine/board_itsybitsy-m4_baremetal.go
index 133bd4626..b38655fdf 100644
--- a/src/machine/board_itsybitsy-m4_baremetal.go
+++ b/src/machine/board_itsybitsy-m4_baremetal.go
@@ -8,13 +8,15 @@ import (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM3_USART_INT,
 		SERCOM: 3,
 	}
 
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
@@ -22,8 +24,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
 }
 
 // I2C on the ItsyBitsy M4.
diff --git a/src/machine/board_lgt92.go b/src/machine/board_lgt92.go
index c95de360b..81fe2220d 100644
--- a/src/machine/board_lgt92.go
+++ b/src/machine/board_lgt92.go
@@ -57,7 +57,8 @@ const (
 var (
 
 	// Console UART (LPUSART1)
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.LPUART1,
 		TxAltFuncSelector: 6,
@@ -65,7 +66,8 @@ var (
 	}
 
 	// Gps UART
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART1,
 		TxAltFuncSelector: 0,
@@ -88,6 +90,6 @@ var (
 
 func init() {
 	// Enable UARTs Interrupts
-	UART0.Interrupt = interrupt.New(stm32.IRQ_AES_RNG_LPUART1, UART0.handleInterrupt)
-	UART1.Interrupt = interrupt.New(stm32.IRQ_USART1, UART1.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_AES_RNG_LPUART1, _UART0.handleInterrupt)
+	UART1.Interrupt = interrupt.New(stm32.IRQ_USART1, _UART1.handleInterrupt)
 }
diff --git a/src/machine/board_matrixportal-m4_baremetal.go b/src/machine/board_matrixportal-m4_baremetal.go
index 4199cbb94..8e0cd8543 100644
--- a/src/machine/board_matrixportal-m4_baremetal.go
+++ b/src/machine/board_matrixportal-m4_baremetal.go
@@ -9,13 +9,15 @@ import (
 
 // UART on the MatrixPortal M4
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM1_USART_INT,
 		SERCOM: 1,
 	}
 
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM4_USART_INT,
 		SERCOM: 4,
@@ -23,8 +25,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1_1, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM4_1, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1_1, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM4_1, _UART2.handleInterrupt)
 }
 
 // I2C on the MatrixPortal M4
diff --git a/src/machine/board_metro-m4-airlift_baremetal.go b/src/machine/board_metro-m4-airlift_baremetal.go
index e5b375392..1564b2406 100644
--- a/src/machine/board_metro-m4-airlift_baremetal.go
+++ b/src/machine/board_metro-m4-airlift_baremetal.go
@@ -8,13 +8,15 @@ import (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM3_USART_INT,
 		SERCOM: 3,
 	}
 
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
@@ -22,8 +24,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
 }
 
 // I2C on the Metro M4.
diff --git a/src/machine/board_nucleof103rb.go b/src/machine/board_nucleof103rb.go
index 8908864d8..0efdd5d8d 100644
--- a/src/machine/board_nucleof103rb.go
+++ b/src/machine/board_nucleof103rb.go
@@ -100,15 +100,16 @@ var (
 	// USART2 is the hardware serial port connected to the onboard ST-LINK
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to USART2.
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    stm32.USART2,
 	}
-	UART2 = &UART0
+	UART2 = UART0
 )
 
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, _UART0.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_nucleof722ze.go b/src/machine/board_nucleof722ze.go
index 32a6e2564..4c1a2cd2f 100644
--- a/src/machine/board_nucleof722ze.go
+++ b/src/machine/board_nucleof722ze.go
@@ -32,17 +32,18 @@ var (
 	// USART3 is the hardware serial port connected to the onboard ST-LINK
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to USART2.
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART3,
 		TxAltFuncSelector: UART_ALT_FN,
 		RxAltFuncSelector: UART_ALT_FN,
 	}
-	UART1 = &UART0
+	UART1 = UART0
 )
 
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART3, UART0.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART3, _UART0.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_nucleol031k6.go b/src/machine/board_nucleol031k6.go
index d5fddebf4..dc80b50db 100644
--- a/src/machine/board_nucleol031k6.go
+++ b/src/machine/board_nucleol031k6.go
@@ -64,13 +64,14 @@ var (
 	// USART2 is the hardware serial port connected to the onboard ST-LINK
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to USART2.
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART2,
 		TxAltFuncSelector: 4,
 		RxAltFuncSelector: 4,
 	}
-	UART1 = &UART0
+	UART1 = UART0
 
 	// I2C1 is documented, alias to I2C0 as well
 	I2C1 = &I2C{
@@ -88,5 +89,5 @@ var (
 )
 
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, _UART0.handleInterrupt)
 }
diff --git a/src/machine/board_nucleol432kc.go b/src/machine/board_nucleol432kc.go
index cb92a9613..bb5133d26 100644
--- a/src/machine/board_nucleol432kc.go
+++ b/src/machine/board_nucleol432kc.go
@@ -66,13 +66,14 @@ var (
 	// USART2 is the hardware serial port connected to the onboard ST-LINK
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to USART2.
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART2,
 		TxAltFuncSelector: 7,
 		RxAltFuncSelector: 3,
 	}
-	UART1 = &UART0
+	UART1 = UART0
 
 	// I2C1 is documented, alias to I2C0 as well
 	I2C1 = &I2C{
@@ -90,5 +91,5 @@ var (
 )
 
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, _UART0.handleInterrupt)
 }
diff --git a/src/machine/board_nucleol552ze.go b/src/machine/board_nucleol552ze.go
index d7fc67e99..a20285c4a 100644
--- a/src/machine/board_nucleol552ze.go
+++ b/src/machine/board_nucleol552ze.go
@@ -32,13 +32,14 @@ var (
 	// LPUART1 is the hardware serial port connected to the onboard ST-LINK
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to LPUART1.
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.LPUART1,
 		TxAltFuncSelector: UART_ALT_FN,
 		RxAltFuncSelector: UART_ALT_FN,
 	}
-	UART1 = &UART0
+	UART1 = UART0
 )
 
 const (
@@ -56,5 +57,5 @@ var (
 )
 
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_LPUART1, UART0.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_LPUART1, _UART0.handleInterrupt)
 }
diff --git a/src/machine/board_p1am-100_baremetal.go b/src/machine/board_p1am-100_baremetal.go
index 2bbf33aa9..e50dd4464 100644
--- a/src/machine/board_p1am-100_baremetal.go
+++ b/src/machine/board_p1am-100_baremetal.go
@@ -9,7 +9,8 @@ import (
 
 // UART1 on the P1AM-100 connects to the normal TX/RX pins.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM3_USART,
 		SERCOM: 5,
@@ -17,7 +18,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5, _UART1.handleInterrupt)
 }
 
 // I2C on the P1AM-100.
diff --git a/src/machine/board_pybadge_baremetal.go b/src/machine/board_pybadge_baremetal.go
index b11ab1579..2e4e89bc7 100644
--- a/src/machine/board_pybadge_baremetal.go
+++ b/src/machine/board_pybadge_baremetal.go
@@ -8,13 +8,15 @@ import (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM5_USART_INT,
 		SERCOM: 5,
 	}
 
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART_INT,
 		SERCOM: 0,
@@ -22,8 +24,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
 }
 
 // I2C on the ItsyBitsy M4.
diff --git a/src/machine/board_pyportal_baremetal.go b/src/machine/board_pyportal_baremetal.go
index ef554022c..82a4e3340 100644
--- a/src/machine/board_pyportal_baremetal.go
+++ b/src/machine/board_pyportal_baremetal.go
@@ -8,7 +8,8 @@ import (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM4_USART_INT,
 		SERCOM: 4,
@@ -16,7 +17,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, _UART1.handleInterrupt)
 }
 
 // I2C on the PyPortal.
diff --git a/src/machine/board_qtpy.go b/src/machine/board_qtpy.go
index e21e288a3..883a32ba6 100644
--- a/src/machine/board_qtpy.go
+++ b/src/machine/board_qtpy.go
@@ -59,7 +59,8 @@ const (
 
 // UART1 on the QT Py M0.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART,
 		SERCOM: 0,
@@ -67,7 +68,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, _UART1.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_stm32f4disco.go b/src/machine/board_stm32f4disco.go
index 5b292e1a2..8c3976ab9 100644
--- a/src/machine/board_stm32f4disco.go
+++ b/src/machine/board_stm32f4disco.go
@@ -27,18 +27,19 @@ const (
 )
 
 var (
-	UART0 = UART{
+	UART0  = &_UART0
+	_UART0 = UART{
 		Buffer:            NewRingBuffer(),
 		Bus:               stm32.USART2,
 		TxAltFuncSelector: AF7_USART1_2_3,
 		RxAltFuncSelector: AF7_USART1_2_3,
 	}
-	UART1 = &UART0
+	UART1 = UART0
 )
 
 // set up RX IRQ handler. Follow similar pattern for other UARTx instances
 func init() {
-	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, _UART0.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_teensy36.go b/src/machine/board_teensy36.go
index f0eccecd3..0808b4b35 100644
--- a/src/machine/board_teensy36.go
+++ b/src/machine/board_teensy36.go
@@ -80,11 +80,11 @@ const (
 )
 
 var (
-	TeensyUART1 = &UART0
-	TeensyUART2 = &UART1
-	TeensyUART3 = &UART2
-	TeensyUART4 = &UART3
-	TeensyUART5 = &UART4
+	TeensyUART1 = UART0
+	TeensyUART2 = UART1
+	TeensyUART3 = UART2
+	TeensyUART4 = UART3
+	TeensyUART5 = UART4
 )
 
 const (
diff --git a/src/machine/board_teensy40.go b/src/machine/board_teensy40.go
index 792c0d3dc..7f0781f02 100644
--- a/src/machine/board_teensy40.go
+++ b/src/machine/board_teensy40.go
@@ -90,13 +90,13 @@ const (
 
 func init() {
 	// register any interrupt handlers for this board's peripherals
-	UART1.Interrupt = interrupt.New(nxp.IRQ_LPUART6, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(nxp.IRQ_LPUART4, UART2.handleInterrupt)
-	UART3.Interrupt = interrupt.New(nxp.IRQ_LPUART2, UART3.handleInterrupt)
-	UART4.Interrupt = interrupt.New(nxp.IRQ_LPUART3, UART4.handleInterrupt)
-	UART5.Interrupt = interrupt.New(nxp.IRQ_LPUART8, UART5.handleInterrupt)
-	UART6.Interrupt = interrupt.New(nxp.IRQ_LPUART1, UART6.handleInterrupt)
-	UART7.Interrupt = interrupt.New(nxp.IRQ_LPUART7, UART7.handleInterrupt)
+	UART1.Interrupt = interrupt.New(nxp.IRQ_LPUART6, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(nxp.IRQ_LPUART4, _UART2.handleInterrupt)
+	UART3.Interrupt = interrupt.New(nxp.IRQ_LPUART2, _UART3.handleInterrupt)
+	UART4.Interrupt = interrupt.New(nxp.IRQ_LPUART3, _UART4.handleInterrupt)
+	UART5.Interrupt = interrupt.New(nxp.IRQ_LPUART8, _UART5.handleInterrupt)
+	UART6.Interrupt = interrupt.New(nxp.IRQ_LPUART1, _UART6.handleInterrupt)
+	UART7.Interrupt = interrupt.New(nxp.IRQ_LPUART7, _UART7.handleInterrupt)
 }
 
 // #=====================================================#
@@ -136,8 +136,9 @@ const (
 )
 
 var (
-	UART0 = &UART1 // alias UART0 to UART1
-	UART1 = UART{
+	UART0  = UART1 // alias UART0 to UART1
+	UART1  = &_UART1
+	_UART1 = UART{
 		Bus:      nxp.LPUART6,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
@@ -150,7 +151,8 @@ var (
 			sel: &nxp.IOMUXC.LPUART6_TX_SELECT_INPUT,
 		},
 	}
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Bus:      nxp.LPUART4,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
@@ -163,7 +165,8 @@ var (
 			sel: &nxp.IOMUXC.LPUART4_TX_SELECT_INPUT,
 		},
 	}
-	UART3 = UART{
+	UART3  = &_UART3
+	_UART3 = UART{
 		Bus:      nxp.LPUART2,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
@@ -176,7 +179,8 @@ var (
 			sel: &nxp.IOMUXC.LPUART2_TX_SELECT_INPUT,
 		},
 	}
-	UART4 = UART{
+	UART4  = &_UART4
+	_UART4 = UART{
 		Bus:      nxp.LPUART3,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
@@ -189,7 +193,8 @@ var (
 			sel: &nxp.IOMUXC.LPUART3_TX_SELECT_INPUT,
 		},
 	}
-	UART5 = UART{
+	UART5  = &_UART5
+	_UART5 = UART{
 		Bus:      nxp.LPUART8,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
@@ -202,7 +207,8 @@ var (
 			sel: &nxp.IOMUXC.LPUART8_TX_SELECT_INPUT,
 		},
 	}
-	UART6 = UART{
+	UART6  = &_UART6
+	_UART6 = UART{
 		Bus:      nxp.LPUART1,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
@@ -210,7 +216,8 @@ var (
 		//   RX: D24 (PA12 [AD_B0_12])
 		//   TX: D25 (PA13 [AD_B0_13])
 	}
-	UART7 = UART{
+	UART7  = &_UART7
+	_UART7 = UART{
 		Bus:      nxp.LPUART7,
 		Buffer:   NewRingBuffer(),
 		txBuffer: NewRingBuffer(),
diff --git a/src/machine/board_trinket.go b/src/machine/board_trinket.go
index 8535fdfe2..6305cb708 100644
--- a/src/machine/board_trinket.go
+++ b/src/machine/board_trinket.go
@@ -47,7 +47,8 @@ const (
 
 // UART1 on the Trinket M0.
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM0_USART,
 		SERCOM: 0,
@@ -55,7 +56,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, _UART1.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_wioterminal_baremetal.go b/src/machine/board_wioterminal_baremetal.go
index bd909f033..a8657f914 100644
--- a/src/machine/board_wioterminal_baremetal.go
+++ b/src/machine/board_wioterminal_baremetal.go
@@ -8,14 +8,16 @@ import (
 )
 
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM2_USART_INT,
 		SERCOM: 2,
 	}
 
 	// RTL8720D
-	UART2 = UART{
+	UART2  = &_UART2
+	_UART2 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM1_USART_INT,
 		SERCOM: 1,
@@ -23,8 +25,8 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, UART2.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, _UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, _UART2.handleInterrupt)
 }
 
 // I2C on the Wio Terminal
diff --git a/src/machine/board_xiao.go b/src/machine/board_xiao.go
index 05316ed45..b18a44e3c 100644
--- a/src/machine/board_xiao.go
+++ b/src/machine/board_xiao.go
@@ -62,7 +62,8 @@ const (
 
 // UART1 on the Xiao
 var (
-	UART1 = UART{
+	UART1  = &_UART1
+	_UART1 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    sam.SERCOM4_USART,
 		SERCOM: 4,
@@ -70,7 +71,7 @@ var (
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, UART1.handleInterrupt)
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, _UART1.handleInterrupt)
 }
 
 // I2C pins
diff --git a/src/machine/machine_atmega.go b/src/machine/machine_atmega.go
index e3f2e7695..6d9a5eda6 100644
--- a/src/machine/machine_atmega.go
+++ b/src/machine/machine_atmega.go
@@ -124,7 +124,8 @@ func (i2c *I2C) readByte() byte {
 // UART
 var (
 	// UART0 is the hardware serial port on the AVR.
-	UART0 = UART{Buffer: NewRingBuffer()}
+	UART0  = &_UART0
+	_UART0 = UART{Buffer: NewRingBuffer()}
 )
 
 // UART on the AVR.
@@ -133,7 +134,7 @@ type UART struct {
 }
 
 // Configure the UART on the AVR. Defaults to 9600 baud on Arduino.
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 	if config.BaudRate == 0 {
 		config.BaudRate = 9600
 	}
@@ -165,7 +166,7 @@ func (uart UART) Configure(config UARTConfig) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart UART) WriteByte(c byte) error {
+func (uart *UART) WriteByte(c byte) error {
 	// Wait until UART buffer is not busy.
 	for !avr.UCSR0A.HasBits(avr.UCSR0A_UDRE0) {
 	}
diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index 058099cde..a9a024379 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -515,7 +515,7 @@ const (
 )
 
 // Configure the UART.
-func (uart UART) Configure(config UARTConfig) error {
+func (uart *UART) Configure(config UARTConfig) error {
 	// Default baud rate to 115200.
 	if config.BaudRate == 0 {
 		config.BaudRate = 115200
@@ -614,7 +614,7 @@ func (uart UART) Configure(config UARTConfig) error {
 }
 
 // SetBaudRate sets the communication speed for the UART.
-func (uart UART) SetBaudRate(br uint32) {
+func (uart *UART) SetBaudRate(br uint32) {
 	// Asynchronous fractional mode (Table 24-2 in datasheet)
 	//   BAUD = fref / (sampleRateValue * fbaud)
 	// (multiply by 8, to calculate fractional piece)
@@ -628,7 +628,7 @@ func (uart UART) SetBaudRate(br uint32) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart UART) WriteByte(c byte) error {
+func (uart *UART) WriteByte(c byte) error {
 	// wait until ready to receive
 	for !uart.Bus.INTFLAG.HasBits(sam.SERCOM_USART_INTFLAG_DRE) {
 	}
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index f21d0173d..4b6333896 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -961,7 +961,7 @@ const (
 )
 
 // Configure the UART.
-func (uart UART) Configure(config UARTConfig) error {
+func (uart *UART) Configure(config UARTConfig) error {
 	// Default baud rate to 115200.
 	if config.BaudRate == 0 {
 		config.BaudRate = 115200
@@ -1064,7 +1064,7 @@ func (uart UART) Configure(config UARTConfig) error {
 }
 
 // SetBaudRate sets the communication speed for the UART.
-func (uart UART) SetBaudRate(br uint32) {
+func (uart *UART) SetBaudRate(br uint32) {
 	// Asynchronous fractional mode (Table 24-2 in datasheet)
 	//   BAUD = fref / (sampleRateValue * fbaud)
 	// (multiply by 8, to calculate fractional piece)
@@ -1078,7 +1078,7 @@ func (uart UART) SetBaudRate(br uint32) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart UART) WriteByte(c byte) error {
+func (uart *UART) WriteByte(c byte) error {
 	// wait until ready to receive
 	for !uart.Bus.INTFLAG.HasBits(sam.SERCOM_USART_INT_INTFLAG_DRE) {
 	}
diff --git a/src/machine/machine_esp32.go b/src/machine/machine_esp32.go
index fd4fa062f..ee3f61de1 100644
--- a/src/machine/machine_esp32.go
+++ b/src/machine/machine_esp32.go
@@ -252,9 +252,12 @@ func (p Pin) mux() *volatile.Register32 {
 }
 
 var (
-	UART0 = UART{Bus: esp.UART0, Buffer: NewRingBuffer()}
-	UART1 = UART{Bus: esp.UART1, Buffer: NewRingBuffer()}
-	UART2 = UART{Bus: esp.UART2, Buffer: NewRingBuffer()}
+	UART0  = &_UART0
+	_UART0 = UART{Bus: esp.UART0, Buffer: NewRingBuffer()}
+	UART1  = &_UART1
+	_UART1 = UART{Bus: esp.UART1, Buffer: NewRingBuffer()}
+	UART2  = &_UART2
+	_UART2 = UART{Bus: esp.UART2, Buffer: NewRingBuffer()}
 )
 
 type UART struct {
@@ -262,14 +265,14 @@ type UART struct {
 	Buffer *RingBuffer
 }
 
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 	if config.BaudRate == 0 {
 		config.BaudRate = 115200
 	}
 	uart.Bus.CLKDIV.Set(peripheralClock / config.BaudRate)
 }
 
-func (uart UART) WriteByte(b byte) error {
+func (uart *UART) WriteByte(b byte) error {
 	for (uart.Bus.STATUS.Get()>>16)&0xff >= 128 {
 		// Read UART_TXFIFO_CNT from the status register, which indicates how
 		// many bytes there are in the transmit buffer. Wait until there are
diff --git a/src/machine/machine_esp8266.go b/src/machine/machine_esp8266.go
index 19c5dd0af..e8a9ecf64 100644
--- a/src/machine/machine_esp8266.go
+++ b/src/machine/machine_esp8266.go
@@ -140,7 +140,8 @@ func (p Pin) PortMaskClear() (*uint32, uint32) {
 }
 
 // UART0 is a hardware UART that supports both TX and RX.
-var UART0 = UART{Buffer: NewRingBuffer()}
+var UART0 = &_UART0
+var _UART0 = UART{Buffer: NewRingBuffer()}
 
 type UART struct {
 	Buffer *RingBuffer
@@ -148,7 +149,7 @@ type UART struct {
 
 // Configure the UART baud rate. TX and RX pins are fixed by the hardware so
 // cannot be modified and will be ignored.
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 	if config.BaudRate == 0 {
 		config.BaudRate = 115200
 	}
@@ -157,7 +158,7 @@ func (uart UART) Configure(config UARTConfig) {
 
 // WriteByte writes a single byte to the output buffer. Note that the hardware
 // includes a buffer of 128 bytes which will be used first.
-func (uart UART) WriteByte(c byte) error {
+func (uart *UART) WriteByte(c byte) error {
 	for (esp.UART0.UART_STATUS.Get()>>16)&0xff >= 128 {
 		// Wait until the TX buffer has room.
 	}
diff --git a/src/machine/machine_fe310.go b/src/machine/machine_fe310.go
index 3af8acc47..ebd85971e 100644
--- a/src/machine/machine_fe310.go
+++ b/src/machine/machine_fe310.go
@@ -56,17 +56,18 @@ type UART struct {
 }
 
 var (
-	UART0 = UART{Bus: sifive.UART0, Buffer: NewRingBuffer()}
+	UART0  = &_UART0
+	_UART0 = UART{Bus: sifive.UART0, Buffer: NewRingBuffer()}
 )
 
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 	// Assuming a 16Mhz Crystal (which is Y1 on the HiFive1), the divisor for a
 	// 115200 baud rate is 138.
 	sifive.UART0.DIV.Set(138)
 	sifive.UART0.TXCTRL.Set(sifive.UART_TXCTRL_ENABLE)
 	sifive.UART0.RXCTRL.Set(sifive.UART_RXCTRL_ENABLE)
 	sifive.UART0.IE.Set(sifive.UART_IE_RXWM) // enable the receive interrupt (only)
-	intr := interrupt.New(sifive.IRQ_UART0, UART0.handleInterrupt)
+	intr := interrupt.New(sifive.IRQ_UART0, _UART0.handleInterrupt)
 	intr.SetPriority(5)
 	intr.Enable()
 }
@@ -83,7 +84,7 @@ func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	uart.Receive(c)
 }
 
-func (uart UART) WriteByte(c byte) {
+func (uart *UART) WriteByte(c byte) {
 	for sifive.UART0.TXDATA.Get()&sifive.UART_TXDATA_FULL != 0 {
 	}
 
diff --git a/src/machine/machine_generic.go b/src/machine/machine_generic.go
index 16948a494..697af241f 100644
--- a/src/machine/machine_generic.go
+++ b/src/machine/machine_generic.go
@@ -7,7 +7,7 @@ package machine
 var (
 	SPI0  = SPI{0}
 	I2C0  = &I2C{0}
-	UART0 = UART{0}
+	UART0 = &UART{0}
 )
 
 const (
@@ -124,34 +124,34 @@ type UARTConfig struct {
 }
 
 // Configure the UART.
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 	uartConfigure(uart.Bus, config.TX, config.RX)
 }
 
 // Read from the UART.
-func (uart UART) Read(data []byte) (n int, err error) {
+func (uart *UART) Read(data []byte) (n int, err error) {
 	return uartRead(uart.Bus, &data[0], len(data)), nil
 }
 
 // Write to the UART.
-func (uart UART) Write(data []byte) (n int, err error) {
+func (uart *UART) Write(data []byte) (n int, err error) {
 	return uartWrite(uart.Bus, &data[0], len(data)), nil
 }
 
 // Buffered returns the number of bytes currently stored in the RX buffer.
-func (uart UART) Buffered() int {
+func (uart *UART) Buffered() int {
 	return 0
 }
 
 // ReadByte reads a single byte from the UART.
-func (uart UART) ReadByte() (byte, error) {
+func (uart *UART) ReadByte() (byte, error) {
 	var b byte
 	uartRead(uart.Bus, &b, 1)
 	return b, nil
 }
 
 // WriteByte writes a single byte to the UART.
-func (uart UART) WriteByte(b byte) error {
+func (uart *UART) WriteByte(b byte) error {
 	uartWrite(uart.Bus, &b, 1)
 	return nil
 }
diff --git a/src/machine/machine_k210.go b/src/machine/machine_k210.go
index f009e1529..232c942bf 100644
--- a/src/machine/machine_k210.go
+++ b/src/machine/machine_k210.go
@@ -338,10 +338,11 @@ type UART struct {
 }
 
 var (
-	UART0 = UART{Bus: kendryte.UARTHS, Buffer: NewRingBuffer()}
+	UART0  = &_UART0
+	_UART0 = UART{Bus: kendryte.UARTHS, Buffer: NewRingBuffer()}
 )
 
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 
 	// Use default baudrate  if not set.
 	if config.BaudRate == 0 {
@@ -366,7 +367,7 @@ func (uart UART) Configure(config UARTConfig) {
 	// Enable interrupts on receive.
 	uart.Bus.IE.Set(kendryte.UARTHS_IE_RXWM)
 
-	intr := interrupt.New(kendryte.IRQ_UARTHS, UART0.handleInterrupt)
+	intr := interrupt.New(kendryte.IRQ_UARTHS, _UART0.handleInterrupt)
 	intr.SetPriority(5)
 	intr.Enable()
 }
@@ -383,7 +384,7 @@ func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	uart.Receive(c)
 }
 
-func (uart UART) WriteByte(c byte) {
+func (uart *UART) WriteByte(c byte) {
 	for uart.Bus.TXDATA.Get()&kendryte.UARTHS_TXDATA_FULL != 0 {
 	}
 
diff --git a/src/machine/machine_nrf.go b/src/machine/machine_nrf.go
index c49096e84..ee883ccc5 100644
--- a/src/machine/machine_nrf.go
+++ b/src/machine/machine_nrf.go
@@ -137,12 +137,13 @@ type UART struct {
 
 // UART
 var (
-	// NRF_UART0 is the hardware UART on the NRF SoC.
-	NRF_UART0 = UART{Buffer: NewRingBuffer()}
+	// UART0 is the hardware UART on the NRF SoC.
+	_NRF_UART0 = UART{Buffer: NewRingBuffer()}
+	NRF_UART0  = &_NRF_UART0
 )
 
 // Configure the UART.
-func (uart UART) Configure(config UARTConfig) {
+func (uart *UART) Configure(config UARTConfig) {
 	// Default baud rate to 115200.
 	if config.BaudRate == 0 {
 		config.BaudRate = 115200
@@ -164,13 +165,13 @@ func (uart UART) Configure(config UARTConfig) {
 	nrf.UART0.INTENSET.Set(nrf.UART_INTENSET_RXDRDY_Msk)
 
 	// Enable RX IRQ.
-	intr := interrupt.New(nrf.IRQ_UART0, NRF_UART0.handleInterrupt)
+	intr := interrupt.New(nrf.IRQ_UART0, _NRF_UART0.handleInterrupt)
 	intr.SetPriority(0xc0) // low priority
 	intr.Enable()
 }
 
 // SetBaudRate sets the communication speed for the UART.
-func (uart UART) SetBaudRate(br uint32) {
+func (uart *UART) SetBaudRate(br uint32) {
 	// Magic: calculate 'baudrate' register from the input number.
 	// Every value listed in the datasheet will be converted to the
 	// correct register value, except for 192600. I suspect the value
@@ -185,7 +186,7 @@ func (uart UART) SetBaudRate(br uint32) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart UART) WriteByte(c byte) error {
+func (uart *UART) WriteByte(c byte) error {
 	nrf.UART0.EVENTS_TXDRDY.Set(0)
 	nrf.UART0.TXD.Set(uint32(c))
 	for nrf.UART0.EVENTS_TXDRDY.Get() == 0 {
diff --git a/src/machine/machine_nrf51.go b/src/machine/machine_nrf51.go
index fe89da4d1..4615a5490 100644
--- a/src/machine/machine_nrf51.go
+++ b/src/machine/machine_nrf51.go
@@ -19,7 +19,7 @@ func (p Pin) getPortPin() (*nrf.GPIO_Type, uint32) {
 	return nrf.GPIO, uint32(p)
 }
 
-func (uart UART) setPins(tx, rx Pin) {
+func (uart *UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSELTXD.Set(uint32(tx))
 	nrf.UART0.PSELRXD.Set(uint32(rx))
 }
diff --git a/src/machine/machine_nrf52.go b/src/machine/machine_nrf52.go
index 50ccde368..441200282 100644
--- a/src/machine/machine_nrf52.go
+++ b/src/machine/machine_nrf52.go
@@ -51,7 +51,7 @@ func (p Pin) getPortPin() (*nrf.GPIO_Type, uint32) {
 	return nrf.P0, uint32(p)
 }
 
-func (uart UART) setPins(tx, rx Pin) {
+func (uart *UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSELTXD.Set(uint32(tx))
 	nrf.UART0.PSELRXD.Set(uint32(rx))
 }
diff --git a/src/machine/machine_nrf52833.go b/src/machine/machine_nrf52833.go
index a7b8ecf00..1920b4e67 100644
--- a/src/machine/machine_nrf52833.go
+++ b/src/machine/machine_nrf52833.go
@@ -71,7 +71,7 @@ func (p Pin) getPortPin() (*nrf.GPIO_Type, uint32) {
 	}
 }
 
-func (uart UART) setPins(tx, rx Pin) {
+func (uart *UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSEL.TXD.Set(uint32(tx))
 	nrf.UART0.PSEL.RXD.Set(uint32(rx))
 }
diff --git a/src/machine/machine_nrf52840.go b/src/machine/machine_nrf52840.go
index 1767802de..d7d6ae2b3 100644
--- a/src/machine/machine_nrf52840.go
+++ b/src/machine/machine_nrf52840.go
@@ -67,7 +67,7 @@ func (p Pin) getPortPin() (*nrf.GPIO_Type, uint32) {
 	}
 }
 
-func (uart UART) setPins(tx, rx Pin) {
+func (uart *UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSEL.TXD.Set(uint32(tx))
 	nrf.UART0.PSEL.RXD.Set(uint32(rx))
 }
diff --git a/src/machine/machine_nxpmk66f18_uart.go b/src/machine/machine_nxpmk66f18_uart.go
index 690e2841c..2d8eae016 100644
--- a/src/machine/machine_nxpmk66f18_uart.go
+++ b/src/machine/machine_nxpmk66f18_uart.go
@@ -101,18 +101,25 @@ type UART struct {
 	Interrupt    interrupt.Interrupt
 }
 
-var UART0 = UART{UART_Type: nxp.UART0, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART0, DefaultRX: defaultUART0RX, DefaultTX: defaultUART0TX}
-var UART1 = UART{UART_Type: nxp.UART1, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART1, DefaultRX: defaultUART1RX, DefaultTX: defaultUART1TX}
-var UART2 = UART{UART_Type: nxp.UART2, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART2, DefaultRX: defaultUART2RX, DefaultTX: defaultUART2TX}
-var UART3 = UART{UART_Type: nxp.UART3, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART3, DefaultRX: defaultUART3RX, DefaultTX: defaultUART3TX}
-var UART4 = UART{UART_Type: nxp.UART4, SCGC: &nxp.SIM.SCGC1, SCGCMask: nxp.SIM_SCGC1_UART4, DefaultRX: defaultUART4RX, DefaultTX: defaultUART4TX}
+var (
+	UART0  = &_UART0
+	UART1  = &_UART1
+	UART2  = &_UART2
+	UART3  = &_UART3
+	UART4  = &_UART4
+	_UART0 = UART{UART_Type: nxp.UART0, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART0, DefaultRX: defaultUART0RX, DefaultTX: defaultUART0TX}
+	_UART1 = UART{UART_Type: nxp.UART1, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART1, DefaultRX: defaultUART1RX, DefaultTX: defaultUART1TX}
+	_UART2 = UART{UART_Type: nxp.UART2, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART2, DefaultRX: defaultUART2RX, DefaultTX: defaultUART2TX}
+	_UART3 = UART{UART_Type: nxp.UART3, SCGC: &nxp.SIM.SCGC4, SCGCMask: nxp.SIM_SCGC4_UART3, DefaultRX: defaultUART3RX, DefaultTX: defaultUART3TX}
+	_UART4 = UART{UART_Type: nxp.UART4, SCGC: &nxp.SIM.SCGC1, SCGCMask: nxp.SIM_SCGC1_UART4, DefaultRX: defaultUART4RX, DefaultTX: defaultUART4TX}
+)
 
 func init() {
-	UART0.Interrupt = interrupt.New(nxp.IRQ_UART0_RX_TX, UART0.handleStatusInterrupt)
-	UART1.Interrupt = interrupt.New(nxp.IRQ_UART1_RX_TX, UART1.handleStatusInterrupt)
-	UART2.Interrupt = interrupt.New(nxp.IRQ_UART2_RX_TX, UART2.handleStatusInterrupt)
-	UART3.Interrupt = interrupt.New(nxp.IRQ_UART3_RX_TX, UART3.handleStatusInterrupt)
-	UART4.Interrupt = interrupt.New(nxp.IRQ_UART4_RX_TX, UART4.handleStatusInterrupt)
+	UART0.Interrupt = interrupt.New(nxp.IRQ_UART0_RX_TX, _UART0.handleStatusInterrupt)
+	UART1.Interrupt = interrupt.New(nxp.IRQ_UART1_RX_TX, _UART1.handleStatusInterrupt)
+	UART2.Interrupt = interrupt.New(nxp.IRQ_UART2_RX_TX, _UART2.handleStatusInterrupt)
+	UART3.Interrupt = interrupt.New(nxp.IRQ_UART3_RX_TX, _UART3.handleStatusInterrupt)
+	UART4.Interrupt = interrupt.New(nxp.IRQ_UART4_RX_TX, _UART4.handleStatusInterrupt)
 }
 
 // Configure the UART.
diff --git a/src/machine/machine_stm32l0.go b/src/machine/machine_stm32l0.go
index f4df17aba..8dab461b5 100644
--- a/src/machine/machine_stm32l0.go
+++ b/src/machine/machine_stm32l0.go
@@ -144,14 +144,14 @@ func (p Pin) enableClock() {
 //---------- UART related types and code
 
 // Configure the UART.
-func (uart UART) configurePins(config UARTConfig) {
+func (uart *UART) configurePins(config UARTConfig) {
 	// enable the alternate functions on the TX and RX pins
 	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
 	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
 }
 
 // UART baudrate calc based on the bus and clockspeed
-func (uart UART) getBaudRateDivisor(baudRate uint32) uint32 {
+func (uart *UART) getBaudRateDivisor(baudRate uint32) uint32 {
 	var clock, rate uint32
 	switch uart.Bus {
 	case stm32.LPUART1:
diff --git a/src/machine/uart.go b/src/machine/uart.go
index 971ff23ec..38046fbae 100644
--- a/src/machine/uart.go
+++ b/src/machine/uart.go
@@ -27,7 +27,7 @@ type UARTConfig struct {
 //
 
 // Read from the RX buffer.
-func (uart UART) Read(data []byte) (n int, err error) {
+func (uart *UART) Read(data []byte) (n int, err error) {
 	// check if RX buffer is empty
 	size := uart.Buffered()
 	if size == 0 {
@@ -49,7 +49,7 @@ func (uart UART) Read(data []byte) (n int, err error) {
 }
 
 // Write data to the UART.
-func (uart UART) Write(data []byte) (n int, err error) {
+func (uart *UART) Write(data []byte) (n int, err error) {
 	for _, v := range data {
 		uart.WriteByte(v)
 	}
@@ -58,7 +58,7 @@ func (uart UART) Write(data []byte) (n int, err error) {
 
 // ReadByte reads a single byte from the RX buffer.
 // If there is no data in the buffer, returns an error.
-func (uart UART) ReadByte() (byte, error) {
+func (uart *UART) ReadByte() (byte, error) {
 	// check if RX buffer is empty
 	buf, ok := uart.Buffer.Get()
 	if !ok {
@@ -68,12 +68,12 @@ func (uart UART) ReadByte() (byte, error) {
 }
 
 // Buffered returns the number of bytes currently stored in the RX buffer.
-func (uart UART) Buffered() int {
+func (uart *UART) Buffered() int {
 	return int(uart.Buffer.Used())
 }
 
 // Receive handles adding data to the UART's data buffer.
 // Usually called by the IRQ handler for a machine.
-func (uart UART) Receive(data byte) {
+func (uart *UART) Receive(data byte) {
 	uart.Buffer.Put(data)
 }