Update twi.c

SpenceKonde · web-flow · commit 51468220e25a · 2021-01-17T02:22:59.000-05:00
diff --git a/megaavr/libraries/Wire/src/utility/twi.c b/megaavr/libraries/Wire/src/utility/twi.c
@@ -204,9 +204,12 @@ void TWI_MasterSetBaud(uint32_t frequency) {
     t_rise = 1000;
   }
 
-  uint32_t baud = ((F_CPU / 1000 / freq_khz) - (((F_CPU * t_rise) / 1000) / 1000) / 1000 - 10) / 2;
-  TWI0.MBAUD = (uint8_t)baud;
-
+  // uint32_t baud = ((F_CPU / 1000 / freq_khz) - (((F_CPU * t_rise) / 1000) / 1000) / 1000 - 10) / 2;
+  // TWI0.MBAUD = (uint8_t)baud;
+  // Prevent an integer overflow that can break the baud rate! 
+  // Arduino megaAVR #90.
+  uint32_t baud = (F_CPU / frequency - F_CPU / 1000 / 1000 * t_rise / 1000 - 10) / 2;
+	TWI0.MBAUD = (uint8_t)baud;
 }
 
 /*! \brief TWI write transaction.

Original file line number	Diff line number	Diff line change
`@@ -204,9 +204,12 @@ void TWI_MasterSetBaud(uint32_t frequency) {`
`204`	`204`	`t_rise = 1000;`
`205`	`205`	`}`
`206`	`206`
`207`		`- uint32_t baud = ((F_CPU / 1000 / freq_khz) - (((F_CPU * t_rise) / 1000) / 1000) / 1000 - 10) / 2;`
`208`		`- TWI0.MBAUD = (uint8_t)baud;`
`209`		`-`
	`207`	`+ // uint32_t baud = ((F_CPU / 1000 / freq_khz) - (((F_CPU * t_rise) / 1000) / 1000) / 1000 - 10) / 2;`
	`208`	`+ // TWI0.MBAUD = (uint8_t)baud;`
	`209`	`+ // Prevent an integer overflow that can break the baud rate!`
	`210`	`+ // Arduino megaAVR #90.`
	`211`	`+ uint32_t baud = (F_CPU / frequency - F_CPU / 1000 / 1000 * t_rise / 1000 - 10) / 2;`
	`212`	`+ TWI0.MBAUD = (uint8_t)baud;`
`210`	`213`	`}`
`211`	`214`
`212`	`215`	`/*! \brief TWI write transaction.`