feat(flasher_stub): Increase CPU frequency and write/read speeds over native USB (USB-OTG)

flasher_stub/include/soc_support.h

@@ -45,7 +45,8 @@
 #define WITH_USB_OTG 1
 #endif // ESP32S3
 
-#define USE_MAX_CPU_FREQ WITH_USB_JTAG_SERIAL // Increase CPU freq only when USB-JTAG/Serial is used
+// Increase CPU freq to speed up read/write operations over USB
+#define USE_MAX_CPU_FREQ (WITH_USB_JTAG_SERIAL || WITH_USB_OTG)
 
 /**********************************************************
  * Per-SOC based peripheral register base addresses
@@ -69,6 +70,7 @@
 #define GPIO_BASE_REG       0x3f404000
 #define USB_BASE_REG        0x60080000
 #define RTCCNTL_BASE_REG    0x3f408000
+#define SYSTEM_BASE_REG     0x3F4C0000
 #endif
 
 #ifdef ESP32S3
@@ -319,6 +321,20 @@
 #define SYSTEM_SOC_CLK_MAX            1
 #endif // ESP32C3
 
+#ifdef ESP32S2
+#define SYSTEM_CPU_PER_CONF_REG       (SYSTEM_BASE_REG + 0x018)
+#define SYSTEM_CPUPERIOD_SEL_M        ((SYSTEM_CPUPERIOD_SEL_V)<<(SYSTEM_CPUPERIOD_SEL_S))
+#define SYSTEM_CPUPERIOD_SEL_V        0x3
+#define SYSTEM_CPUPERIOD_SEL_S        0
+#define SYSTEM_CPUPERIOD_MAX          2  // CPU_CLK frequency is 240 MHz
+
+#define SYSTEM_SYSCLK_CONF_REG        (SYSTEM_BASE_REG + 0x08C)
+#define SYSTEM_SOC_CLK_SEL_M          ((SYSTEM_SOC_CLK_SEL_V)<<(SYSTEM_SOC_CLK_SEL_S))
+#define SYSTEM_SOC_CLK_SEL_V          0x3
+#define SYSTEM_SOC_CLK_SEL_S          10
+#define SYSTEM_SOC_CLK_MAX            1
+#endif // ESP32S2
+
 /**********************************************************
  * Per-SOC security info buffer size
  */

flasher_stub/include/stub_io.h

@@ -54,3 +54,9 @@ void stub_io_idle_hook(void);
 #if WITH_USB_JTAG_SERIAL
 bool stub_uses_usb_jtag_serial(void);
 #endif
+
+/* Checks if USB-OTG is being currently used.
+ */
+#if WITH_USB_OTG
+bool stub_uses_usb_otg(void);
+#endif

flasher_stub/stub_flasher.c

@@ -49,12 +49,26 @@ static uint8_t calculate_checksum(uint8_t *buf, int length)
 }
 
 #if USE_MAX_CPU_FREQ
+static bool can_use_max_cpu_freq()
+{
+  /* Check if any of available USB modes are being used. */
+  #if WITH_USB_OTG && !WITH_USB_JTAG_SERIAL
+  return stub_uses_usb_otg();
+  #elif !WITH_USB_OTG && WITH_USB_JTAG_SERIAL
+  return stub_uses_usb_jtag_serial();
+  #elif WITH_USB_OTG && WITH_USB_JTAG_SERIAL
+  return stub_uses_usb_otg() || stub_uses_usb_jtag_serial();
+  #else
+  return false;
+  #endif
+}
+
 static uint32_t cpu_per_conf_reg = 0;
 static uint32_t sysclk_conf_reg = 0;
 
 static void set_max_cpu_freq()
 {
-  if (stub_uses_usb_jtag_serial())
+  if (can_use_max_cpu_freq())
   {
     /* Set CPU frequency to max. This also increases SPI speed. */
     cpu_per_conf_reg = READ_REG(SYSTEM_CPU_PER_CONF_REG);
@@ -68,7 +82,7 @@ static void reset_cpu_freq()
 {
   /* Restore saved sysclk_conf and cpu_per_conf registers.
      Use only if set_max_cpu_freq() has been called. */
-  if (stub_uses_usb_jtag_serial() && sysclk_conf_reg != 0 && cpu_per_conf_reg != 0)
+  if (can_use_max_cpu_freq() && sysclk_conf_reg != 0 && cpu_per_conf_reg != 0)
   {
     WRITE_REG(SYSTEM_CPU_PER_CONF_REG, (READ_REG(SYSTEM_CPU_PER_CONF_REG) & ~SYSTEM_CPUPERIOD_SEL_M) | (cpu_per_conf_reg & SYSTEM_CPUPERIOD_SEL_M));
     WRITE_REG(SYSTEM_SYSCLK_CONF_REG, (READ_REG(SYSTEM_SYSCLK_CONF_REG) & ~SYSTEM_SOC_CLK_SEL_M) | (sysclk_conf_reg & SYSTEM_SOC_CLK_SEL_M));
@@ -444,8 +458,10 @@ void stub_main()
   cmd_loop();
 
   /* if cmd_loop returns, it's due to ESP_RUN_USER_CODE command. */
+
   #if USE_MAX_CPU_FREQ
     reset_cpu_freq();
   #endif // USE_MAX_CPU_FREQ
+
   return;
 }

flasher_stub/stub_io.c

@@ -116,7 +116,7 @@ static void stub_cdcacm_write_char(char ch)
     }
 }
 
-static bool stub_uses_usb_otg(void)
+bool stub_uses_usb_otg(void)
 {
   UartDevice *uart = GetUartDevice();