MSP430 stdout: Support more CPU frequencies

src/arch/msp430fr5969lp/driver/stdout.cc

 #include "driver/stdout.h"
 #include <msp430.h>
 
+/*
+ * Baud rate calculation according to datasheet:
+ * N := f_{BRCLK} / Baudrate = F_CPU / 115200 in our case
+ * if N <= 16: OS16 = 0, UCBR0 = int(N)
+ * if N > 16: OS16 = 1, UCBR0 = int(N/16), UCBRF0 = int(((n/16) - int(n/16)) * 16) = int(N)%16
+ * Set UCBRS0 according to table 21-4
+ */
+
 void StandardOutput::setup()
 {
 	UCA0CTLW0 |= UCSWRST;
+#if F_CPU == 16000000UL
+	// 16M / 115200 == 138.88889 -> UCOS16 = 1, UCBR0 = 16, UCBRF0 = 10, UCBRS0 = 0xf7 ("0.8751")
+	UCA0CTLW0 = UCSWRST | UCSSEL__SMCLK;
+	UCA0MCTLW = UCOS16 | (10<<4) | 0xF700;
+	UCA0BR0 = 8;
+#elif F_CPU == 8000000UL
+	// 8M / 115200 == 69.444444 -> UCOS16 = 1, UCBR0 = 4, UCBRF0 = 5, UCBRS0 = 0x55 ("0.4378")
+	UCA0CTLW0 = UCSWRST | UCSSEL__SMCLK;
+	UCA0MCTLW = UCOS16 | (5<<4) | 0x5500;
+	UCA0BR0 = 4;
+#elif F_CPU == 4000000UL
+	// 4M / 115200 == 34.722222 -> UCOS16 = 1, UCBR0 = 2, UCBRF0 = 2, UCBRS0 = 0xbb ("0.7147")
+	UCA0CTLW0 = UCSWRST | UCSSEL__SMCLK;
+	UCA0MCTLW = UCOS16 | (2<<4) | 0xbb00;
+	UCA0BR0 = 2;
+#elif F_CPU == 1000000UL
+	// 1M / 115200 == 8.6805556 -> UCOS16 = 0, UCBR0 = 8, UCBRF0 = 0, UCBRS0 = 0xd6 ("0.6667")
 	UCA0CTLW0 = UCSWRST | UCSSEL__SMCLK;
-	UCA0MCTLW = UCOS16 | (10<<5) | 0xF700;
+	UCA0MCTLW = 0x5500;
 	UCA0BR0 = 8;
+#else
+#error Unsupported F_CPU
+#endif
 
 	UCA0IRCTL = 0;
 	UCA0ABCTL = 0;