Fix crystal frequency detection for ESP32-C2 and ESP8266 (#314)

* Add a workaround for setting baud rate on 26MHz ESP32-C2

* Detect  crystal frequency for ESP32-C2

* Fix clock divider value for ESP8266

Author: jessebraham

espflash/src/flasher/mod.rs

@@ -348,13 +348,13 @@ impl Flasher {
 
         // Now that we have established a connection and detected the chip and flash
         // size, we can set the baud rate of the connection to the configured value.
-        if let Some(b) = speed {
+        if let Some(baud) = speed {
             match flasher.chip {
                 Chip::Esp8266 => (), // Not available
                 _ => {
-                    if b > 115_200 {
+                    if baud > 115_200 {
                         warn!("Setting baud rate higher than 115,200 can cause issues");
-                        flasher.change_baud(b)?;
+                        flasher.change_baud(baud)?;
                     }
                 }
             }
@@ -776,16 +776,29 @@ impl Flasher {
             false => 0,
         };
 
+        let target = self.chip.into_target();
+        let xtal_freq = target.crystal_freq(&mut self.connection)?;
+
+        // Probably this is just a temporary solution until the next chip revision.
+        //
+        // The ROM code thinks it uses a 40 MHz XTAL. Recompute the baud rate in order
+        // to trick the ROM code to set the correct baud rate for a 26 MHz XTAL.
+        let mut new_baud = speed;
+        if self.chip == Chip::Esp32c2 && !self.use_stub && xtal_freq == 26 {
+            new_baud = new_baud * 40 / 26;
+        }
+
         self.connection
             .with_timeout(CommandType::ChangeBaud.timeout(), |connection| {
                 connection.command(Command::ChangeBaud {
-                    new_baud: speed,
+                    new_baud,
                     prior_baud,
                 })
             })?;
         self.connection.set_baud(speed)?;
-        std::thread::sleep(Duration::from_secs_f32(0.05));
+        sleep(Duration::from_secs_f32(0.05));
         self.connection.flush()?;
+
         Ok(())
     }
 

espflash/src/targets/esp32c2.rs

@@ -29,6 +29,11 @@ const PARAMS: Esp32Params = Esp32Params::new(
     include_bytes!("../../resources/bootloaders/esp32c2-bootloader.bin"),
 );
 
+const UART_CLKDIV_REG: u32 = 0x6000_0014;
+const UART_CLKDIV_MASK: u32 = 0xfffff;
+
+const XTAL_CLK_DIVIDER: u32 = 1;
+
 /// ESP32-C2 Target
 pub struct Esp32c2;
 
@@ -61,9 +66,12 @@ impl Target for Esp32c2 {
         Ok(self.read_efuse(connection, 17)? >> 16 & 0xf)
     }
 
-    fn crystal_freq(&self, _connection: &mut Connection) -> Result<u32, Error> {
-        // The ESP32-C2's XTAL has a fixed frequency of 40MHz.
-        Ok(40)
+    fn crystal_freq(&self, connection: &mut Connection) -> Result<u32, Error> {
+        let uart_div = connection.read_reg(UART_CLKDIV_REG)? & UART_CLKDIV_MASK;
+        let est_xtal = (connection.get_baud()? * uart_div) / 1_000_000 / XTAL_CLK_DIVIDER;
+        let norm_xtal = if est_xtal > 33 { 40 } else { 26 };
+
+        Ok(norm_xtal)
     }
 
     fn flash_frequency_encodings(&self) -> HashMap<FlashFrequency, u8> {

espflash/src/targets/esp8266.rs

@@ -20,7 +20,7 @@ const FLASH_RANGES: &[Range<u32>] = &[
 const UART_CLKDIV_REG: u32 = 0x6000_0014;
 const UART_CLKDIV_MASK: u32 = 0xfffff;
 
-const XTAL_CLK_DIVIDER: u32 = 1;
+const XTAL_CLK_DIVIDER: u32 = 2;
 
 /// ESP8266 Target
 pub struct Esp8266;