bricks/stm32: make .fw_info section optional

This renames the .boot section to .fw_info and makes it optional. This
frees up 320 bytes on Move hub.

Also fill in some missing values while we are touching this in case LEGO
ever updates their firmware to read them.

bricks/essentialhub/essential_hub.ld

@@ -15,4 +15,5 @@ MEMORY
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 320K
 }
 
+"FW_INFO_OFFSET" = 0x200;
 _minimum_stack_size = 8K;

bricks/stm32/common.ld

@@ -15,9 +15,9 @@ SECTIONS
         _fw_isr_vector_src = .;   /* The isr vector table must be copied to SRAM since the
                                      firmware doesn't start at the beginning of the flash memory */
         KEEP(*(.isr_vector)) /* isr vector table */
-        . = 0x200;
-        *(.boot)           /* .boot section for info read during firmware update */
-        KEEP(*(.boot))
+        . = DEFINED(FW_INFO_OFFSET) ? FW_INFO_OFFSET : .;
+        *(.fw_info) /* .fw_info section for info read during SPIKE firmware update */
+        KEEP(*(.fw_info))
         *(.text)           /* .text sections (code) */
         *(.text*)          /* .text* sections (code) */
         *(.rodata)         /* .rodata sections (constants, strings, etc.) */
@@ -93,6 +93,7 @@ SECTIONS
     .checksum :
     {
         . = ALIGN(4);
+        _checksum = .;
         LONG(CHECKSUM)
     } >FLASH
 

lib/pbio/platform/essential_hub/platform.c

@@ -9,6 +9,7 @@
 
 #include "pbio/uartdev.h"
 #include "pbio/light_matrix.h"
+#include "pbio/version.h"
 
 #include "../../drv/adc/adc_stm32_hal.h"
 #include "../../drv/bluetooth/bluetooth_btstack_control_gpio.h"
@@ -27,18 +28,23 @@
 typedef struct {
     const char *fw_ver;
     const uint32_t *checksum;
-    const uint8_t *reserved;
+    const void *reserved;
     const char *id_string;
-} boot_t;
+    const void *reserved2;
+} lego_fw_info_t;
 
-const boot_t __attribute__((section(".boot"))) boot = {
+// defined in linker script
+extern const uint32_t _checksum;
+
+const lego_fw_info_t __attribute__((section(".fw_info"))) fw_info = {
     // These values are not used.
-    .fw_ver = NULL,
-    .checksum = NULL,
+    .fw_ver = PBIO_VERSION_STR,
+    .checksum = &_checksum,
     .reserved = NULL,
     // This value is checked when installing the firmware
     // via the 'firmware' MicroPython module on the hub.
     .id_string = "LEGO Technic Small Hub(0x000D)",
+    .reserved2 = NULL,
 };
 
 enum {