stm32: fix flash_ec stm32 serial EC programming mode

Proper sequence of events when enabling STM32 monitor mode is as
follows:

  - bootp0 pin level is set to 'high'

  - chip is reset

  - the programmer starts sending sync bytes over the UART

This patch implements this sequence in flash_stm32().

In cases when 'cold_reset' control is not available this function will
fail, as this means that the STM32 chip can not be reset.

When programming over Cr50 a servod control to enter bit bang mode is
issued.

Newer Cr50 versions support baud rates up to 57600, but until the new
Cr50 version is released, 9600 bps should be used as the default. A new
command line option is being added to allow specify UART speed when
programming in bit bang mode.

BRANCH=cr50, cr50-mp
BUG=b:62539385
TEST=successfully ran to completion (100 iterations) the following
     script when programming Scarlet when servo is connected over
     Cr50:

    count=0;
    while ./util/flash_ec --board scarlet --image <image path>; do
      count=$(( count + 1 ))
      echo "succeeded $count times"
      if [ $count == 100 ]; then
        break
      fi
      sleep 3
    done

Change-Id: Ib3242a92c94f64214ffd1f290b97c2660ce21360
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1171915
Reviewed-by: Mary Ruthven <mruthven@chromium.org>

1 files changed, 23 insertions, 17 deletions

diff --git a/util/flash_ec b/util/flash_ec
index 32b46978b3..9f6ee74736 100755
--- a/util/flash_ec
+++ b/util/flash_ec
@@ -184,8 +184,12 @@ VALID_CHIP_COMBO["grunt.npcx_uut"]="ccd_cr50"
 VALID_CHIP_COMBO["grunt.npcx_spi"]="servo"
 
 DEFAULT_PORT="${SERVOD_PORT:-9999}"
+BITBANG_RATE="9600"  # Could be overwritten by a command line option.
 
 # Flags
+DEFINE_integer bitbang_rate "${BITBANG_RATE}" \
+	"UART baud rate to use when bit bang programming, "\
+"standard UART rates from 9600 to 57600 are supported."
 DEFINE_string board "${DEFAULT_BOARD}" \
 	"The board to run debugger on."
 DEFINE_string chip "" \
@@ -880,6 +884,11 @@ function flash_flashrom() {
 
 function flash_stm32() {
 	local log_option
+	local STM32MON
+
+	if ! $(servo_has_cold_reset); then
+		die "Cold reset must be available for STM32 programming"
+	fi
 
 	TOOL_PATH="${EC_DIR}/build/${BOARD}/util:$PATH"
 	STM32MON=$(PATH="${TOOL_PATH}" which stm32mon)
@@ -892,40 +901,37 @@ function flash_stm32() {
 	info "${MCU} UART pty : ${EC_UART}"
 	claim_pty ${EC_UART}
 
+	# Make sure EC reboots in serial monitor mode.
+	ec_enable_boot0 "bitbang"
+
+	# Pulse EC reset.
+	ec_reset
+
 	if ! on_raiden && [[ "${SERVO_TYPE}" =~ "servo" ]] ; then
 		dut_control ${MCU}_uart_en:on
 	fi
 	dut_control ${MCU}_uart_parity:even
 
 	if [[ "${SERVO_TYPE}" =~ "ccd_cr50" ]] ; then
-		# TODO(b/77965217): remove when cr50 stops clobbering bitbang
-		# when it notices the AP/EC turn off.
-		dut_control cold_reset:on
-		sleep 2
-		dut_control ${MCU}_uart_baudrate:9600
+		case "${FLAGS_bitbang_rate}" in
+			(9600|19200|38400|57600) : ;;
+			(*) die
+                            "${FLAGS_bitbang_rate} is not a valid bit bang rate"
+                            ;;
+		esac
+		info "Programming at ${FLAGS_bitbang_rate} baud"
+		dut_control ${MCU}_uart_baudrate:"${FLAGS_bitbang_rate}"
 		dut_control ${MCU}_uart_bitbang_en:on
 	else
 		dut_control ${MCU}_uart_baudrate:115200
-
-		if $(servo_has_warm_reset); then
-			dut_control warm_reset:on
-		fi
 	fi
 
-	# Force the EC to boot in serial monitor mode
-	ec_enable_boot0 "bitbang"
-
 	# Add a delay long enough for cr50 to update the ccdstate. Cr50 updates
 	# ccdstate once a second, so a 2 second delay should be safe.
 	if [[ "${SERVO_TYPE}" =~ "ccd_cr50" ]] ; then
 		sleep 2
 	fi
 
-	# Reset the EC
-	if $(servo_has_cold_reset); then
-		ec_reset
-	fi
-
         if [ -n "${FLAGS_logfile}" ]; then
 		log_option="-L ${FLAGS_logfile}"
 		info "Saving log in ${FLAGS_logfile}"