16550 UART Driver: Add a configuration option to indicate the the THR empty bit is inverted. This is the the case for the moxART SoC. Based comments from Anton D. Kachalov

ChangeLog

@@ -10770,4 +10770,7 @@
 	* configs/moxa: Moxa NP51x0 series of 2-port advanced RS-232/422/485
 	  serial device servers.  From Anton D. Kachalov (2015-07-29).
 	* drivers/net/ and include/nuttx/net: Add support for a Faraday
-	  FTMAC100 Ethernet MAC Driver.  From Anton D. Kachalov (2015-07-29).
+	* FTMAC100 Ethernet MAC Driver.  From Anton D. Kachalov (2015-07-29).
+	* 16550 UART Driver: Add a configuration option to indicate the the
+	  THR empty bit is inverted.  This is the the case for the moxART SoC.
+	  Based comments from Anton D. Kachalov (2015-07-29).

configs

@@ -1 +1 @@
-Subproject commit e098a90e99ca1268e121cebd7942d7c17a48e114
+Subproject commit 73e7501f1278e5e0e0919baf0c217176b8cc02a6

drivers/serial/Kconfig

@@ -19,11 +19,13 @@ config 16550_UART
 	default n
 
 if 16550_UART
+
 config 16550_UART0
 	bool "16550 UART0"
 	default n
 
 if 16550_UART0
+
 config 16550_UART0_BASE
 	hex "16550 UART0 base address"
 
@@ -82,13 +84,14 @@ config 16550_UART0_OFLOWCONTROL
 	---help---
 		Enable 16550 UART0 CTS flow control
 
-endif
+endif # 16550_UART0
 
 config 16550_UART1
 	bool "16550 UART1"
 	default n
 
 if 16550_UART1
+
 config 16550_UART1_BASE
 	hex "16550 UART1 base address"
 
@@ -147,13 +150,14 @@ config 16550_UART1_OFLOWCONTROL
 	---help---
 		Enable 16550 UART1 CTS flow control
 
-endif
+endif # 16550_UART1
 
 config 16550_UART2
 	bool "16550 UART2"
 	default n
 
 if 16550_UART2
+
 config 16550_UART2_BASE
 	hex "16550 UART2 base address"
 
@@ -212,13 +216,14 @@ config 16550_UART2_OFLOWCONTROL
 	---help---
 		Enable 16550 UART2 CTS flow control
 
-endif
+endif # 16550_UART2
 
 config 16550_UART3
 	bool "16550 UART3"
 	default n
 
 if 16550_UART3
+
 config 16550_UART3_BASE
 	hex "16550 UART3 base address"
 
@@ -277,7 +282,7 @@ config 16550_UART3_OFLOWCONTROL
 	---help---
 		Enable 16550 UART3 CTS flow control
 
-endif
+endif # 16550_UART3
 
 choice
 	prompt "16550 Serial Console"
@@ -303,7 +308,7 @@ config 16550_UART3_SERIAL_CONSOLE
 config 16550_NO_SERIAL_CONSOLE
 	bool "No 16550 serial console"
 
-endchoice
+endchoice # 16550 Serial Console
 
 config 16550_SUPRESS_CONFIG
 	bool "Suppress 16550 configuration"
@@ -332,7 +337,18 @@ config 16550_ADDRWIDTH
 	---help---
 		The bit width of registers.  Options are 8, 16, or 32. Default: 8
 
-endif
+config 16550_THRNE
+	bool "Use THRNE"
+	default n if !ARCH_CHIP_MOXART
+	default y if ARCH_CHIP_MOXART
+	---help---
+		The 16550 UART has a bit in the line status register, THRE, that
+		indicates that the Transmit Holding Register (THR) is Empty (N).
+		This bit is inverted in at least one variant (the moxART SoC).
+		In that case, this setting must be included to use this bit as
+		THR *Not* Empty (THRNE).
+
+endif # 16550_UART
 
 #
 # MCU serial peripheral driver?

drivers/serial/uart_16550.c

@@ -1057,7 +1057,11 @@ static bool u16550_txempty(struct uart_dev_s *dev)
 
 static void u16550_putc(struct u16550_s *priv, int ch)
 {
+#ifdef CONFIG_16550_THRNE
+  while ((u16550_serialin(priv, UART_LSR_OFFSET) & UART_LSR_THRNE) == 0);
+#else
   while ((u16550_serialin(priv, UART_LSR_OFFSET) & UART_LSR_THRE) != 0);
+#endif
   u16550_serialout(priv, UART_THR_OFFSET, (uart_datawidth_t)ch);
 }
 

include/nuttx/serial/uart_16550.h

@@ -299,7 +299,11 @@
 #define UART_LSR_PE                  (1 << 2)  /* Bit 2:  Parity Error */
 #define UART_LSR_FE                  (1 << 3)  /* Bit 3:  Framing Error */
 #define UART_LSR_BI                  (1 << 4)  /* Bit 4:  Break Interrupt */
-#define UART_LSR_THRE                (1 << 5)  /* Bit 5:  Transmitter Holding Register Empty */
+#ifdef CONFIG_16550_THRNE
+#  define UART_LSR_THRNE             (1 << 5)  /* Bit 5:  Transmitter Holding Register Not Empty */
+#else
+#  define UART_LSR_THRE              (1 << 5)  /* Bit 5:  Transmitter Holding Register Empty */
+#endif
 #define UART_LSR_TEMT                (1 << 6)  /* Bit 6:  Transmitter Empty */
 #define UART_LSR_RXFE                (1 << 7)  /* Bit 7:  Error in RX FIFO (RXFE) */