Add CRC to the boot sector. Use .bin for remote flashing

Author: cpq

step-7-webserver/pico-w5500/Makefile

@@ -36,7 +36,7 @@ test: update
 	grep 'Ethernet: up' /tmp/output.txt
 
 update: build
-	curl --fail -su :$(VCON_API_KEY) $(DEVICE_URL)/ota?uf2=1 --data-binary @firmware.uf2
+	curl --fail -su :$(VCON_API_KEY) $(DEVICE_URL)/ota --data-binary @firmware.bin
 
 clean:
 	$(RM) firmware.* bin2uf2

step-7-webserver/pico-w5500/link.ld

@@ -12,6 +12,8 @@ SECTIONS {
 
   .boot : ALIGN(4) {
     KEEP(*(.boot))
+    . = 256 - 4;
+    LONG(0xcccccccc) /* RP2040 expects CRC in the last 4 bytes of this block */
   } > boot
 
   .text : ALIGN(4) {