i2csoft: add source code for each target

i2csoft/i2csoft_esp32.go

@@ -7,16 +7,10 @@ import (
 	"device"
 )
 
+// wait waits for half the time of the SCL operation interval. It is set to
+// about 100 kHz.
 func (i2c *I2C) wait() {
-	// atsamd51
-	// 10 : about 387kHz
-	// 56 : about 99kHz
-
-	wait := 10
-	if i2c.baudrate < 400*1e3 {
-		wait = 56
-	}
-
+	wait := 60
 	for i := 0; i < wait; i++ {
 		device.Asm(`nop`)
 	}