Hardware target reset support

src/picoprobe_config.h

@@ -52,6 +52,9 @@
 #define PROBE_PIN_SWCLK PROBE_PIN_OFFSET + 0 // 2
 #define PROBE_PIN_SWDIO PROBE_PIN_OFFSET + 1 // 3
 
+// Target reset config
+#define PROBE_PIN_RESET 6
+
 // UART config
 #define PICOPROBE_UART_TX 4
 #define PICOPROBE_UART_RX 5

src/probe.c

@@ -68,11 +68,12 @@ struct _probe {
 static struct _probe probe;
 
 enum PROBE_CMDS {
-    PROBE_INVALID = 0,    // Invalid command
-    PROBE_WRITE_BITS = 1, // Host wants us to write bits
-    PROBE_READ_BITS = 2,  // Host wants us to read bits
-    PROBE_SET_FREQ = 3,   // Set TCK
-    PROBE_RESET = 4,      // Reset all state
+    PROBE_INVALID      = 0, // Invalid command
+    PROBE_WRITE_BITS   = 1, // Host wants us to write bits
+    PROBE_READ_BITS    = 2, // Host wants us to read bits
+    PROBE_SET_FREQ     = 3, // Set TCK
+    PROBE_RESET        = 4, // Reset all state
+    PROBE_TARGET_RESET = 5, // Reset target
 };
 
 struct __attribute__((__packed__)) probe_cmd_hdr {
@@ -93,6 +94,12 @@ void probe_set_swclk_freq(uint freq_khz) {
     pio_sm_set_clkdiv_int_frac(pio0, PROBE_SM, divider, 0);
 }
 
+static inline void probe_assert_reset(bool state)
+{
+    /* Change the direction to out to drive pin to 0 or to in to emulate open drain */
+    gpio_set_dir(PROBE_PIN_RESET, state);
+}
+
 static inline void probe_write_bits(uint bit_count, uint8_t data_byte) {
     DEBUG_PINS_SET(probe_timing, DBG_PIN_WRITE);
     pio_sm_put_blocking(pio0, PROBE_SM, bit_count - 1);
@@ -137,6 +144,11 @@ void probe_init() {
     // Make sure SWDIO has a pullup on it. Idle state is high
     gpio_pull_up(PROBE_PIN_SWDIO);
 
+    // Target reset pin: pull up, input to emulate open drain pin
+    gpio_pull_up(PROBE_PIN_RESET);
+    // gpio_init will leave the pin cleared and set as input
+    gpio_init(PROBE_PIN_RESET);
+
     uint offset = pio_add_program(pio0, &probe_program);
     probe.offset = offset;
 
@@ -251,6 +263,8 @@ void probe_handle_pkt(void) {
             // TODO: Is there anything to do after a reset?
             // tx len and rx len should already be 0
             ;
+        } else if (hdr->cmd == PROBE_TARGET_RESET) {
+            probe_assert_reset(hdr->bits);
         }
     }
     probe.rx_len = 0;