hosted: assert ntrst as part of connecting

Assert the nTRST when connecting via JTAG. This is required for targets that
use this pin to enable the JTAG circuitry.

Signed-off-by: Sean Cross <sean@xobs.io>

src/platforms/hosted/dap.c

@@ -84,6 +84,7 @@ static bool dap_transfer_configure(uint8_t idle_cycles, uint16_t wait_retries, u
 
 static uint32_t dap_current_clock_freq;
 static bool dap_nrst_state = false;
+static bool dap_ntrst_state = false;
 
 bool dap_connect(void)
 {
@@ -236,6 +237,33 @@ bool dap_nrst_set_val(const bool nrst_state)
 	return response == request.pin_values;
 }
 
+bool dap_ntrst_get_val(void)
+{
+	return dap_ntrst_state;
+}
+
+bool dap_ntrst_set_val(const bool ntrst_state)
+{
+	/* Setup the request for the pin state change request */
+	dap_swj_pins_request_s request = {
+		.request = DAP_SWJ_PINS,
+		/* nRST is active low, so take that into account */
+		.pin_values = ntrst_state ? 0U : DAP_SWJ_nTRST,
+		.selected_pins = DAP_SWJ_nTRST,
+	};
+	/* Tell the hardware to wait for 10µs for the pin to settle */
+	write_le4(request.wait_time, 0, 10);
+	uint8_t response = 0U;
+	/* Execute it and check if it failed */
+	if (!dap_run_cmd(&request, 7U, &response, 1U)) {
+		DEBUG_PROBE("%s failed\n", __func__);
+		return false;
+	}
+	/* Extract the current pin state for the device, de-inverting it */
+	dap_ntrst_state = !(response & DAP_SWJ_nTRST);
+	return response == request.pin_values;
+}
+
 uint32_t dap_read_reg(adiv5_debug_port_s *target_dp, const uint8_t reg)
 {
 	const dap_transfer_request_s request = {.request = reg | DAP_TRANSFER_RnW};

src/platforms/hosted/dap.h

@@ -81,6 +81,8 @@ extern uint8_t dap_quirks;
 
 bool dap_connect(void);
 bool dap_disconnect(void);
+bool dap_ntrst_get_val(void);
+bool dap_ntrst_set_val(const bool ntrst_state);
 bool dap_led(dap_led_type_e type, bool state);
 size_t dap_info(dap_info_e requested_info, void *buffer, size_t buffer_length);
 bool dap_set_reset_state(bool nrst_state);

src/platforms/hosted/dap_jtag.c

@@ -52,6 +52,8 @@ bool dap_jtag_init(void)
 	dap_disconnect();
 	dap_mode = DAP_CAP_JTAG;
 	dap_connect();
+	dap_ntrst_set_val(true);
+	dap_ntrst_set_val(false);
 
 	jtag_proc.jtagtap_reset = dap_jtag_reset;
 	jtag_proc.jtagtap_next = dap_jtag_next;