src: Event hooks during firmware load.

Loading the wifi firmware can cause delays on startup which causes
problems for USB. Add some hooks so we can allow background processes to
run.

See micropython/micropython#8904
and note that a change will be needed in micropython and pico-sdk to
define the hook.

Fixes georgerobotics#11

src/cyw43_config.h

@@ -102,3 +102,8 @@
 #ifndef CYW43_FAIL_FAST_CHECK
 #define CYW43_FAIL_FAST_CHECK(res) (res)
 #endif
+
+// This should be defined by the port, to let background processes like usb to run
+#ifndef CYW43_EVENT_POLL_HOOK
+#define CYW43_EVENT_POLL_HOOK
+#endif

src/cyw43_ll.c

@@ -466,6 +466,8 @@ static int cyw43_download_resource(cyw43_int_t *self, uint32_t addr, size_t raw_
     #endif
 
     for (size_t offset = 0; offset < len; offset += block_size) {
+        CYW43_EVENT_POLL_HOOK;
+
         size_t sz = block_size;
         if (offset + sz > len) {
             sz = len - offset;
@@ -1416,6 +1418,8 @@ static void cyw43_clm_load(cyw43_int_t *self, const uint8_t *clm_ptr, size_t clm
 
     const size_t clm_dload_chunk_len = CLM_CHUNK_LEN;
     for (size_t off = 0; off < clm_len; off += clm_dload_chunk_len) {
+        CYW43_EVENT_POLL_HOOK;
+
         uint32_t len = clm_dload_chunk_len;
         uint16_t flag = 1 << 12; // DLOAD_HANDLER_VER
         if (off == 0) {
@@ -1497,7 +1501,9 @@ int cyw43_ll_bus_init(cyw43_ll_t *self_in, const uint8_t *mac) {
         }
 
         cyw43_spi_gpio_setup();
+        CYW43_EVENT_POLL_HOOK;
         cyw43_spi_reset();
+        CYW43_EVENT_POLL_HOOK;
 
         // Check test register can be read
         for (int i = 0; i < 10; ++i) {