ServoMicro: Enable Brownout detection with PVD circuit

Enables the programmable voltage detector (PVD) interrupt in
ServoMicro. This interrupt fires when the supply voltage drops
from the expected 3.3V to under 2.3V after power on. This gives
several hundred microseconds of time for the device to respond
to the power reduction.

In order to ensure that the ServoMicro does not enter a
non-responsive state, it triggers a reboot of the system to
restore it to a good configuration.

BRANCH=servo
BUG=chromium:1023715
TEST=Configured GPIO output to trigger on pvd_interrupt()
and verified the interrupt fires during the following
situations using Saleae analyzer:

* USB Power removed from working device
* Ramping supply voltage from 1.5V to 5V with a DC supply
* Repoducing failure condition from crbug/1016051
    1 Connect ServoMicro to Cyan board
    2 dut-control power_state:on
    3 dut-control fw_wp_vref:pp3300
    4 dut-control power_state:off
    5 GPIO toggles and system reset occurs

Change-Id: I721f48ab84b01d52a5f98747cc9d879ff2876a07
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1911759
Reviewed-by: Ruben Rodriguez Buchillon <coconutruben@chromium.org>
Tested-by: Brian Nemec <bnemec@chromium.org>
Commit-Queue: Brian Nemec <bnemec@chromium.org>
Auto-Submit: Brian Nemec <bnemec@chromium.org>
(cherry picked from commit 771dd33b149fb94725edf0e29670207b9a013cb6)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2044707
Reviewed-by: Brian Nemec <bnemec@google.com>
Commit-Queue: Brian Nemec <bnemec@google.com>
Tested-by: Brian Nemec <bnemec@google.com>

8 files changed, 82 insertions, 4 deletions

diff --git a/board/servo_micro/board.c b/board/servo_micro/board.c
index 6524b31442..d8611fd493 100644
--- a/board/servo_micro/board.c
+++ b/board/servo_micro/board.c
@@ -13,6 +13,7 @@
 #include "queue_policies.h"
 #include "registers.h"
 #include "spi.h"
+#include "system.h"
 #include "task.h"
 #include "timer.h"
 #include "update_fw.h"
@@ -673,6 +674,15 @@ const unsigned int i2c_ports_used = ARRAY_SIZE(i2c_ports);
 
 int usb_i2c_board_is_enabled(void) { return 1; }
 
+void pvd_interrupt(void) {
+	/* Clear Pending Register */
+	STM32_EXTI_PR = EXTI_PVD_EVENT;
+	/* Handle recovery by rebooting the system */
+	system_reset(0);
+}
+
+DECLARE_IRQ(STM32_IRQ_PVD, pvd_interrupt, HOOK_PRIO_FIRST);
+
 /******************************************************************************
  * Initialize board.
  */
diff --git a/board/servo_micro/board.h b/board/servo_micro/board.h
index 99fa722fb4..9a0ca5824d 100644
--- a/board/servo_micro/board.h
+++ b/board/servo_micro/board.h
@@ -32,6 +32,10 @@
 /* Optional features */
 #define CONFIG_STM_HWTIMER32
 #define CONFIG_HW_CRC
+#define CONFIG_PVD
+/* See 'Programmable voltage detector characteristics' in the STM32F072x8 Datasheet.
+   PVD Threshold 1 corresponds to a falling voltage threshold of min:2.09V, max:2.27V. */
+#define PVD_THRESHOLD     (1)
 
 /* USB Configuration */
 #define CONFIG_USB
diff --git a/board/servo_v4/board.c b/board/servo_v4/board.c
index bf1c51e267..7661cee20c 100644
--- a/board/servo_v4/board.c
+++ b/board/servo_v4/board.c
@@ -410,6 +410,15 @@ int board_get_version(void)
 	return ver;
 }
 
+void pvd_interrupt(void) {
+	/* Clear Pending Register */
+	STM32_EXTI_PR = EXTI_PVD_EVENT;
+	/* Handle recovery by rebooting the system */
+	system_reset(0);
+}
+
+DECLARE_IRQ(STM32_IRQ_PVD, pvd_interrupt, HOOK_PRIO_FIRST);
+
 static void board_init(void)
 {
 	/* USB to serial queues */
diff --git a/board/servo_v4/board.h b/board/servo_v4/board.h
index 274aa8d6a8..ff46ae13e4 100644
--- a/board/servo_v4/board.h
+++ b/board/servo_v4/board.h
@@ -32,6 +32,10 @@
 /* Optional features */
 #define CONFIG_STM_HWTIMER32
 #define CONFIG_HW_CRC
+#define CONFIG_PVD
+/* See 'Programmable voltage detector characteristics' in the STM32F072x8 Datasheet.
+   PVD Threshold 1 corresponds to a falling voltage threshold of min:2.09V, max:2.27V. */
+#define PVD_THRESHOLD     (1)
 
 /* USB Configuration */
 #define CONFIG_USB
diff --git a/chip/stm32/registers-stm32f0.h b/chip/stm32/registers-stm32f0.h
index 72d3cdb7a6..442edaed9a 100644
--- a/chip/stm32/registers-stm32f0.h
+++ b/chip/stm32/registers-stm32f0.h
@@ -277,6 +277,11 @@
 
 
 /* --- Power / Reset / Clocks --- */
+#define STM32_PWR_CR                REG32(STM32_PWR_BASE + 0x00)
+#define STM32_PWD_PVD_LS_MASK       (0x07 << 5)
+#define STM32_PWD_PVD_LS(n)         ((n & 0x07) << 5)
+#define STM32_PWR_PVDE              BIT(4)
+
 #define STM32_PWR_CSR               REG32(STM32_PWR_BASE + 0x04)
 
 #define STM32_PWR_CSR_EWUP1         BIT(8)
@@ -382,8 +387,8 @@
 #define  RESET_CAUSE_OTHER              0xfe000000
 #define  RESET_CAUSE_RMVF               0x01000000
 /* Power cause in PWR CSR register */
-#define STM32_PWR_RESET_CAUSE STM32_PWR_CSR
-#define STM32_PWR_RESET_CAUSE_CLR STM32_PWR_CR
+#define STM32_PWR_RESET_CAUSE           STM32_PWR_CSR
+#define STM32_PWR_RESET_CAUSE_CLR       STM32_PWR_CR
 #define  RESET_CAUSE_SBF                0x00000002
 #define  RESET_CAUSE_SBF_CLR            0x00000004
 
@@ -528,8 +533,9 @@ typedef volatile struct stm32_spi_regs stm32_spi_regs_t;
 #define STM32_EXTI_SWIER            REG32(STM32_EXTI_BASE + 0x10)
 #define STM32_EXTI_PR               REG32(STM32_EXTI_BASE + 0x14)
 
-#define EXTI_RTC_ALR_EVENT		BIT(17)
-#define EXTI_COMP2_EVENT		BIT(22)
+#define EXTI_PVD_EVENT              BIT(16)
+#define EXTI_RTC_ALR_EVENT          BIT(17)
+#define EXTI_COMP2_EVENT            BIT(22)
 
 /* --- ADC --- */
 #define STM32_ADC_ISR              REG32(STM32_ADC1_BASE + 0x00)
diff --git a/chip/stm32/registers.h b/chip/stm32/registers.h
index 08b9d61e20..5926dda278 100644
--- a/chip/stm32/registers.h
+++ b/chip/stm32/registers.h
@@ -229,6 +229,7 @@ typedef volatile struct timer_ctlr timer_ctlr_t;
 #define STM32_RCC_PB1_USART3		BIT(18)
 #define STM32_RCC_PB1_USART4		BIT(19)
 #define STM32_RCC_PB1_USART5		BIT(20)
+#define STM32_RCC_PB1_PWREN		BIT(28)
 #define STM32_RCC_PB2_SPI1		BIT(12)
 /* Reset causes definitions */
 
diff --git a/chip/stm32/system.c b/chip/stm32/system.c
index 4b0dada71d..3f08e4ef80 100644
--- a/chip/stm32/system.c
+++ b/chip/stm32/system.c
@@ -271,6 +271,38 @@ void chip_pre_init(void)
 		STM32_DBGMCU_APB2FZ |= apb2fz_reg;
 }
 
+#ifdef CONFIG_PVD
+/* Configures the programmable voltage detector to monitor for brown out conditions. */
+static void configure_pvd(void)
+{
+	/* Clear Interrupt Enable Mask Register. */
+	STM32_EXTI_IMR &= ~EXTI_PVD_EVENT;
+
+	/* Clear Rising and Falling Trigger Selection Registers. */
+	STM32_EXTI_RTSR &= ~EXTI_PVD_EVENT;
+	STM32_EXTI_FTSR &= ~EXTI_PVD_EVENT;
+
+	/* Clear the value of the PVD Level Selection. */
+	STM32_PWR_CR &= ~STM32_PWD_PVD_LS_MASK;
+
+	/* Set the new value of the PVD Level Selection. */
+	STM32_PWR_CR |= STM32_PWD_PVD_LS(PVD_THRESHOLD);
+
+	/* Enable Power Clock. */
+	STM32_RCC_APB1ENR |= STM32_RCC_PB1_PWREN;
+
+	/* Configure the NVIC for PVD. */
+	task_enable_irq(STM32_IRQ_PVD);
+
+	/* Configure interrupt mode. */
+	STM32_EXTI_IMR |= EXTI_PVD_EVENT;
+	STM32_EXTI_RTSR |= EXTI_PVD_EVENT;
+
+	/* Enable the PVD Output. */
+	STM32_PWR_CR |= STM32_PWR_PVDE;
+}
+#endif
+
 void system_pre_init(void)
 {
 #ifdef CONFIG_SOFTWARE_PANIC
@@ -349,6 +381,10 @@ void system_pre_init(void)
 		bkpdata_write(BKPDATA_INDEX_SAVED_PANIC_EXCEPTION, 0);
 	}
 #endif
+
+#ifdef CONFIG_PVD
+	configure_pvd();
+#endif
 }
 
 void system_reset(int flags)
diff --git a/include/config.h b/include/config.h
index 6d34b5e5aa..ab6a60e8df 100644
--- a/include/config.h
+++ b/include/config.h
@@ -3009,6 +3009,14 @@
  */
 #undef CONFIG_CPU_PROCHOT_ACTIVE_LOW
 
+/*
+ * Define this option to enable programmable voltage detector which will
+ * trigger an interrupt when the voltage drops below a threshold specified
+ * by the PVD_THRESHOLD which is a chip specific voltage threshold that
+ * must be defined in board.h.
+ */
+#undef CONFIG_PVD
+
 /*****************************************************************************/
 /* Support PWM control */
 #undef CONFIG_PWM