From 31c41b7d9e33d2eff67d3afaf62b0bbc9c8b6940 Mon Sep 17 00:00:00 2001
From: Ondrej Jirman <megous@megous.com>
Date: Sun, 5 Sep 2021 02:26:55 +0200
Subject: [PATCH] Drop I2C bit functions, to make timing easier to modify

I2C to the charger now has clean 100kHz timing. One read command now takes
400us, and one write command takes 300us to execute.
---
 firmware/main.c   | 92 ++++++++++++++++++++++++++---------------------
 i2c-charger-ctl.c |  4 +--
 2 files changed, 53 insertions(+), 43 deletions(-)

diff --git a/firmware/main.c b/firmware/main.c
index 82e5964..0fa2ba9 100644
--- a/firmware/main.c
+++ b/firmware/main.c
@@ -1006,7 +1006,7 @@ static __bit poll_scl_busy(void)
 }
 */
 
-void i2c_start_condition(void)
+static void i2c_start_condition(void)
 {
 	CHG_RELEASE_SDA;
 	delay_us(5);
@@ -1021,7 +1021,7 @@ void i2c_start_condition(void)
 	delay_us(5);
 }
 
-void i2c_stop_condition(void)
+static void i2c_stop_condition(void)
 {
 	CHG_PULL_SDA;
 	delay_us(5);
@@ -1033,68 +1033,78 @@ void i2c_stop_condition(void)
 	delay_us(5);
 }
 
-void i2c_write_bit(__bit b)
+static __bit i2c_write_byte(uint8_t data)
 {
-	if (b)
-		CHG_RELEASE_SDA;
-	else
-		CHG_PULL_SDA;
+	uint8_t i;
+	__bit ack = 1;
+
+	// write data
+	for (i = 0; i < 8; i++) {
+		// write the most-significant bit
+		if (data & 0x80)
+			CHG_RELEASE_SDA;
+		else
+			CHG_PULL_SDA;
+		delay_us(1);
+
+		CHG_RELEASE_SCL;
+		delay_us(5);
+
+		CHG_PULL_SCL;
+		delay_us(1);
+
+		data <<= 1;
+	}
+
 	delay_us(1);
 
-	CHG_RELEASE_SCL;
-	delay_us(5);
-
-	CHG_PULL_SCL;
-	delay_us(1);
-}
-
-__bit i2c_read_bit(void)
-{
-	__bit b;
-
+	// read ack bit
 	CHG_RELEASE_SDA;
-
 	CHG_RELEASE_SCL;
-	delay_us(4);
+	delay_us(3);
 
 	if (CHG_PORT & CHG_SDA)
-		b = 1;
-	else
-		b = 0;
+		ack = 0;
 
 	CHG_PULL_SCL;
 	delay_us(2);
 
-	return b;
+	return ack;
 }
 
-__bit i2c_write_byte(uint8_t data)
-{
-	uint8_t i;
-
-	// write data
-	for (i = 0; i < 8; i++) {
-		i2c_write_bit(data & 0x80);   // write the most-significant bit
-		data <<= 1;
-	}
-
-	// read ack bit
-	return !i2c_read_bit();
-}
-
-uint8_t i2c_read_byte(__bit ack)
+static uint8_t i2c_read_byte(__bit ack)
 {
 	uint8_t data = 0;
 	uint8_t i;
 
+	CHG_RELEASE_SDA;
+
 	// read data
 	for (i = 0; i < 8; i++) {
 		data <<= 1;
-		data |= i2c_read_bit();
+
+		CHG_RELEASE_SCL;
+		delay_us(4);
+
+		if (CHG_PORT & CHG_SDA)
+			data |= 1;
+
+		CHG_PULL_SCL;
+		delay_us(2);
 	}
 
 	// send ack
-	i2c_write_bit(!ack);
+	if (ack)
+		CHG_PULL_SDA;
+	else
+		CHG_RELEASE_SDA;
+	delay_us(1);
+
+	CHG_RELEASE_SCL;
+	delay_us(5);
+
+	CHG_PULL_SCL;
+	delay_us(1);
 	return data;
 }
 
diff --git a/i2c-charger-ctl.c b/i2c-charger-ctl.c
index 3cc8481..18de5c6 100644
--- a/i2c-charger-ctl.c
+++ b/i2c-charger-ctl.c
@@ -130,7 +130,7 @@ uint8_t read_power(int fd, uint8_t reg)
 	syscall_error(ret < 0, "I2C_RDWR failed");
 
 	for (int i = 0; i < 5; i++) {
-		usleep(2000);
+		usleep(700);
 
 		// read the result
 		uint8_t buf2[1] = { REG_SYS_CHG_DATA, };
@@ -183,7 +183,7 @@ void write_power(int fd, uint8_t reg, uint8_t val)
 	syscall_error(ret < 0, "I2C_RDWR failed");
 
 	for (int i = 0; i < 5; i++) {
-		usleep(2000);
+		usleep(700);
 
 		// read the result
 		uint8_t buf2[1] = { REG_SYS_COMMAND, };