From: Michael Gernoth <michael@gernoth.net>
Date: Mon, 23 Aug 2010 17:00:37 +0000 (+0200)
Subject: use 20kHz as I2C frequency
X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/rsbs2/commitdiff_plain/989281f290d774ce78f71c8a420870987407a831

use 20kHz as I2C frequency
---

diff --git a/bmc/i2c.c b/bmc/i2c.c
index d7bb951..bd4d69c 100644
--- a/bmc/i2c.c
+++ b/bmc/i2c.c
@@ -14,9 +14,15 @@ volatile uint8_t i2c_len = 0x00;
 static volatile uint8_t i2c_pos = 0x00;
 volatile uint8_t i2c_done = 0x00;
 
+#define I2C_FREQ 20000UL
+
 void i2c_init()
 {
-	TWBR = 0xff;
+	/* SCLf = F_CPU / (16 + 2 * TWBR * 4^TWPS)
+	 * TWPS is 0 =>
+	 * TWBR = (F_CPU/(2 * SCL)) - 8
+	 */
+	TWBR = (F_CPU/(2*I2C_FREQ))-8;
 	TWAR = BMC_ADDR & 0xfe;
 	TWDR = 0x00;
 	TWCR &= ~((1<<TWSTA) | (1<<TWSTO));