From 18e300efa3ec5e5b78acaa326ad6e525c3e10abd Mon Sep 17 00:00:00 2001
From: kai-morich <mail@kai-morich.de>
Date: Wed, 28 Jul 2021 17:40:17 +0200
Subject: [PATCH] add dedicated handling for Ch34x baud rate 921600

---
 .../hoho/android/usbserial/DeviceTest.java    | 34 ++++++++++++++-
 .../usbserial/driver/Ch34xSerialDriver.java   | 43 ++++++++++++-------
 2 files changed, 60 insertions(+), 17 deletions(-)

diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
index 845e3ed..2fbcfbc 100644
--- a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
@@ -229,8 +229,8 @@ public class DeviceTest {
         doReadWrite(reason, -1);
     }
     private void doReadWrite(String reason, int readWait) throws Exception {
-        byte[] buf1 = new byte[]{ 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16};
-        byte[] buf2 = new byte[]{ 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26};
+        byte[] buf1 = new byte[]{ 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x55, 0x55};
+        byte[] buf2 = new byte[]{ 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x55, 0x55};
         byte[] data;
 
         telnet.write(buf1);
@@ -420,6 +420,36 @@ public class DeviceTest {
         }
     }
 
+    @Test
+    public void Ch34xBaudRate() throws Exception {
+        Assume.assumeTrue("only for Ch34x", usb.serialDriver instanceof Ch34xSerialDriver);
+        usb.open();
+
+        int[] baudRates = {
+                115200, 230400, 256000, 307200, 460800, 921600, 1000000, 1228800
+        };
+        for (int baudRate : baudRates) {
+            telnet.setParameters(baudRate, 8, 1, UsbSerialPort.PARITY_NONE);
+            usb.setParameters(baudRate, 8, 1, UsbSerialPort.PARITY_NONE);
+            doReadWrite(baudRate + "");
+            try {
+                usb.setParameters(baudRate + (1 << 29), 8, 1, UsbSerialPort.PARITY_NONE);
+                doReadWrite(baudRate + "+(1<<29)");
+
+                usb.setParameters(baudRate - 1, 8, 1, UsbSerialPort.PARITY_NONE);
+                doReadWrite(baudRate + "-1");
+
+                usb.setParameters(baudRate + 1, 8, 1, UsbSerialPort.PARITY_NONE);
+                doReadWrite(baudRate + "+1");
+                if (baudRate == 921600)
+                    fail("error expected for " + baudRate + " baud");
+            } catch(AssertionError err) {
+                if (baudRate != 921600)
+                    throw(err);
+            }
+        }
+    }
+
     @Test
     public void baudRate() throws Exception {
         usb.open();
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java
index c0154f6..cb34533 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java
@@ -10,6 +10,9 @@ import android.hardware.usb.UsbDevice;
 import android.hardware.usb.UsbDeviceConnection;
 import android.hardware.usb.UsbEndpoint;
 import android.hardware.usb.UsbInterface;
+import android.util.Log;
+
+import com.hoho.android.usbserial.BuildConfig;
 
 import java.io.IOException;
 import java.util.Collections;
@@ -191,29 +194,39 @@ public class Ch34xSerialDriver implements UsbSerialDriver {
 
 
 		private void setBaudRate(int baudRate) throws IOException {
-			final long CH341_BAUDBASE_FACTOR = 1532620800;
-			final int CH341_BAUDBASE_DIVMAX = 3;
+			long factor;
+			long divisor;
 
-			long factor = CH341_BAUDBASE_FACTOR / baudRate;
-			int divisor = CH341_BAUDBASE_DIVMAX;
+			if (baudRate == 921600) {
+				divisor = 7;
+				factor = 0xf300;
+			} else {
+				final long BAUDBASE_FACTOR = 1532620800;
+				final int BAUDBASE_DIVMAX = 3;
 
-			while ((factor > 0xfff0) && divisor > 0) {
-				factor >>= 3;
-				divisor--;
-					}
-
-			if (factor > 0xfff0) {
-				throw new UnsupportedOperationException("Unsupported baud rate: " + baudRate);
+				if(BuildConfig.DEBUG && (baudRate & (3<<29)) == (1<<29))
+					baudRate &= ~(1<<29); // for testing purpose bypass dedicated baud rate handling
+				factor = BAUDBASE_FACTOR / baudRate;
+				divisor = BAUDBASE_DIVMAX;
+				while ((factor > 0xfff0) && divisor > 0) {
+					factor >>= 3;
+					divisor--;
+				}
+				if (factor > 0xfff0) {
+					throw new UnsupportedOperationException("Unsupported baud rate: " + baudRate);
+				}
+				factor = 0x10000 - factor;
 			}
 
-			factor = 0x10000 - factor;
 			divisor |= 0x0080; // else ch341a waits until buffer full
-			int ret = controlOut(0x9a, 0x1312, (int) ((factor & 0xff00) | divisor));
+			int val1 = (int) ((factor & 0xff00) | divisor);
+			int val2 = (int) (factor & 0xff);
+			Log.d(TAG, String.format("baud rate=%d, 0x1312=0x%04x, 0x0f2c=0x%04x", baudRate, val1, val2));
+			int ret = controlOut(0x9a, 0x1312, val1);
 			if (ret < 0) {
 				throw new IOException("Error setting baud rate: #1)");
 			}
-
-			ret = controlOut(0x9a, 0x0f2c, (int) (factor & 0xff));
+			ret = controlOut(0x9a, 0x0f2c, val2);
 			if (ret < 0) {
 				throw new IOException("Error setting baud rate: #2");
 			}