Test voltage on VREF before enabling target power (mon tpwr), to avoid potential power conflict.

src/command.c

@@ -393,9 +393,16 @@ static bool cmd_target_power(target *t, int argc, const char **argv)
 	} else if (argc == 2) {
 		bool want_enable = false;
 		if (parse_enable_or_disable(argv[1], &want_enable)) {
+			if (want_enable
+				&& !platform_target_get_power()
+				&& platform_target_voltage_sense() > POWER_CONFLICT_THRESHOLD) {
+				/* want to enable target power, but VREF > 0.5V sensed -> cancel */
+				gdb_outf("Target already powered (%s)\n", platform_target_voltage());
+			} else {
 				platform_target_set_power(want_enable);
 				gdb_outf("%s target power\n", want_enable ? "Enabling" : "Disabling");
 			}
+		}
 	} else {
 		gdb_outf("Unrecognized command format\n");
 	}

src/include/platform_support.h

@@ -37,7 +37,9 @@ void platform_timeout_set(platform_timeout *t, uint32_t ms);
 bool platform_timeout_is_expired(platform_timeout *t);
 void platform_delay(uint32_t ms);
 
+#define POWER_CONFLICT_THRESHOLD	5 /* in 0.1V, so 5 stands for 0.5V */
 extern bool connect_assert_srst;
+uint32_t platform_target_voltage_sense(void);
 const char *platform_target_voltage(void);
 int platform_hwversion(void);
 void platform_srst_set_val(bool assert);

src/platforms/native/platform.c

@@ -251,12 +251,16 @@ static void adc_init(void)
 	adc_calibrate(ADC1);
 }
 
-const char *platform_target_voltage(void)
+uint32_t platform_target_voltage_sense(void)
 {
+	/* returns the voltage in volt scaled by 10 (so 33 means 3.3V), except
+	 * for hardware version 1
+	 * this function is only needed for implementations that allow the
+	 * target to be powered from the debug probe
+	 */
 	if (platform_hwversion() == 0)
-		return gpio_get(GPIOB, GPIO0) ? "OK" : "ABSENT!";
+		return 0;
 
-	static char ret[] = "0.0V";
 	const uint8_t channel = 8;
 	adc_set_regular_sequence(ADC1, 1, (uint8_t*)&channel);
 
@@ -265,9 +269,19 @@ const char *platform_target_voltage(void)
 	/* Wait for end of conversion. */
 	while (!adc_eoc(ADC1));
 
-	uint32_t val = adc_read_regular(ADC1) * 99; /* 0-4095 */
+	uint32_t val = adc_read_regular(ADC1); /* 0-4095 */
-	ret[0] = '0' + val / 81910;
+	return (val * 99) / 8191;
-	ret[2] = '0' + (val / 8191) % 10;
+}
+
+const char *platform_target_voltage(void)
+{
+	if (platform_hwversion() == 0)
+		return gpio_get(GPIOB, GPIO0) ? "OK" : "ABSENT!";
+
+	static char ret[] = "0.0V";
+	uint32_t val = platform_target_voltage_sense();
+	ret[0] = '0' + val / 10;
+	ret[2] = '0' + val % 10;
 
 	return ret;
 }

src/remote.c

@@ -296,8 +296,18 @@ static void remotePacketProcessGEN(unsigned i, char *packet)
 
     case REMOTE_PWR_SET:
 #ifdef PLATFORM_HAS_POWER_SWITCH
+		if (packet[2]=='1'
+			&& !platform_target_get_power()
+			&& platform_target_voltage_sense() > POWER_CONFLICT_THRESHOLD)
+		{
+			/* want to enable target power, but voltage > 0.5V sensed
+			 * on the pin -> cancel
+			 */
+			_respond(REMOTE_RESP_ERR,0);
+		} else {
 			platform_target_set_power(packet[2]=='1');
 			_respond(REMOTE_RESP_OK,0);
+		}
 #else
 		_respond(REMOTE_RESP_NOTSUP,0);
 #endif