espnet: WIP support for on-chip WiFi on an ESP32C3

Work in progress. Does not work yet.

Some notes:

  - This requires some changes to TinyGo, look at the espnet branch.
  - The  next step is probably defining all the functions in
    g_wifi_osi_funcs (see espnet.c). Right now it hangs in
    esp_wifi_init_internal, probably a NULL pointer dereference.
  - This is only for the ESP32-C3. This will require some work to work
    on other chips from Espressif.

espnet/espnet.c

@@ -0,0 +1,98 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+#include "espnet.h"
+
+// OS adapter functions.
+// See: esp-idf/components/esp_wifi/include/esp_private/wifi_os_adapter.h
+wifi_osi_funcs_t g_wifi_osi_funcs = {
+    ._version = ESP_WIFI_OS_ADAPTER_VERSION,
+    // TODO: define these functions.
+    ._magic = ESP_WIFI_OS_ADAPTER_MAGIC,
+};
+
+// This is a string constant that is used all over ESP-IDF and is also used by
+// libnet80211.a. The main purpose is to be a fixed pointer that can be compared
+// against etc.
+const char *WIFI_EVENT = "WIFI_EVENT";
+
+// Required by libphy.a
+int phy_printf(const char *format, ...) {
+    va_list args;
+    va_start(args, format);
+    printf("phy: ");
+    int res = vprintf(format, args);
+    va_end(args);
+    return res;
+}
+
+// Required by libpp.a
+int pp_printf(const char *format, ...) {
+    va_list args;
+    va_start(args, format);
+    printf("pp: ");
+    int res = vprintf(format, args);
+    va_end(args);
+    return res;
+}
+
+// Required by libnet80211.a
+int net80211_printf(const char *format, ...) {
+    va_list args;
+    va_start(args, format);
+    printf("net80211: ");
+    int res = vprintf(format, args);
+    va_end(args);
+    return res;
+}
+
+// Source: esp-idf/components/wpa_supplicant/src/utils/common.c
+static int hex2num(char c)
+{
+	if (c >= '0' && c <= '9')
+		return c - '0';
+	if (c >= 'a' && c <= 'f')
+		return c - 'a' + 10;
+	if (c >= 'A' && c <= 'F')
+		return c - 'A' + 10;
+	return -1;
+}
+
+// Source: esp-idf/components/wpa_supplicant/src/utils/common.c
+int hex2byte(const char *hex)
+{
+	int a, b;
+	a = hex2num(*hex++);
+	if (a < 0)
+		return -1;
+	b = hex2num(*hex++);
+	if (b < 0)
+		return -1;
+	return (a << 4) | b;
+}
+
+// Source: esp-idf/components/wpa_supplicant/src/utils/common.c
+/**
+ * hexstr2bin - Convert ASCII hex string into binary data
+ * @hex: ASCII hex string (e.g., "01ab")
+ * @buf: Buffer for the binary data
+ * @len: Length of the text to convert in bytes (of buf); hex will be double
+ * this size
+ * Returns: 0 on success, -1 on failure (invalid hex string)
+ */
+int hexstr2bin(const char *hex, uint8_t *buf, size_t len)
+{
+	size_t i;
+	int a;
+	const char *ipos = hex;
+	uint8_t *opos = buf;
+
+	for (i = 0; i < len; i++) {
+		a = hex2byte(ipos);
+		if (a < 0)
+			return -1;
+		*opos++ = a;
+		ipos += 2;
+	}
+	return 0;
+}