From 7b59c685be0167b67effbeda3eda9fc5c8509116 Mon Sep 17 00:00:00 2001
From: William Vinnicombe <william.vinnicombe@raspberrypi.com>
Date: Tue, 12 Nov 2024 18:50:44 +0000
Subject: [PATCH 1/5] Add simple UART bootloader

The sample binary flashes the LED and prints Hello, world back over the UART interface
---
 README.md                       |   1 +
 bootloaders/CMakeLists.txt      |   2 +
 bootloaders/uart/CMakeLists.txt |  32 +++++++
 bootloaders/uart/uart-pt.json   |  23 +++++
 bootloaders/uart/uart_binary.c  |  65 ++++++++++++++
 bootloaders/uart/uart_boot.c    | 152 ++++++++++++++++++++++++++++++++
 6 files changed, 275 insertions(+)
 create mode 100644 bootloaders/uart/CMakeLists.txt
 create mode 100644 bootloaders/uart/uart-pt.json
 create mode 100644 bootloaders/uart/uart_binary.c
 create mode 100644 bootloaders/uart/uart_boot.c

diff --git a/README.md b/README.md
index 5a436a348..cbdfaff48 100644
--- a/README.md
+++ b/README.md
@@ -55,6 +55,7 @@ App|Description
 App|Description
 ---|---
 [enc_bootloader](bootloaders/encrypted) | A bootloader which decrypts binaries from flash into SRAM. See the separate [README](bootloaders/encrypted/README.md) for more information
+[uart_boot](bootloaders/uart) | A bootloader which boots a separate RP2350 using the UART boot interface. See section 5.8 in the datasheet for more details, including the wiring requirements
 
 ### Clocks
 
diff --git a/bootloaders/CMakeLists.txt b/bootloaders/CMakeLists.txt
index fff349887..849138ab6 100644
--- a/bootloaders/CMakeLists.txt
+++ b/bootloaders/CMakeLists.txt
@@ -1,3 +1,5 @@
+add_subdirectory_exclude_platforms(uart host rp2040)
+
 if (TARGET pico_mbedtls)
     # older clang seem to have a segment overlap issue that confuses picotool
     if (PICO_C_COMPILER_IS_CLANG AND CMAKE_C_COMPILER_VERSION VERSION_LESS "17.0.0")
diff --git a/bootloaders/uart/CMakeLists.txt b/bootloaders/uart/CMakeLists.txt
new file mode 100644
index 000000000..cc0e38caa
--- /dev/null
+++ b/bootloaders/uart/CMakeLists.txt
@@ -0,0 +1,32 @@
+add_executable(uart_boot
+    uart_boot.c
+    )
+
+# pull in common dependencies
+target_link_libraries(uart_boot pico_stdlib hardware_flash)
+
+pico_embed_pt_in_binary(uart_boot ${CMAKE_CURRENT_LIST_DIR}/uart-pt.json)
+pico_set_uf2_family(uart_boot "absolute")
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(uart_boot)
+
+# add url via pico_set_program_url
+example_auto_set_url(uart_boot)
+
+
+add_executable(uart_binary
+    uart_binary.c
+    )
+
+# pull in common dependencies
+target_link_libraries(uart_binary pico_stdlib)
+
+pico_set_binary_type(uart_binary no_flash)
+pico_package_uf2_output(uart_binary 0x10000000)
+
+# create map/bin/hex/uf2 file etc.
+pico_add_extra_outputs(uart_binary)
+
+# call pico_set_program_url to set path to example on github, so users can find the source for an example via picotool
+example_auto_set_url(uart_binary)
diff --git a/bootloaders/uart/uart-pt.json b/bootloaders/uart/uart-pt.json
new file mode 100644
index 000000000..d6ce01299
--- /dev/null
+++ b/bootloaders/uart/uart-pt.json
@@ -0,0 +1,23 @@
+{
+  "version": [1, 0],
+  "unpartitioned": {
+    "families": ["absolute"],
+    "permissions": {
+      "secure": "rw",
+      "nonsecure": "rw",
+      "bootloader": "rw"
+    }
+  },
+  "partitions": [
+    {
+      "start": "128K",
+      "size": "32K",
+      "families": ["rp2350-arm-s"],
+      "permissions": {
+        "secure": "rw",
+        "nonsecure": "rw",
+        "bootloader": "rw"
+      }
+    }
+  ]
+}
\ No newline at end of file
diff --git a/bootloaders/uart/uart_binary.c b/bootloaders/uart/uart_binary.c
new file mode 100644
index 000000000..e3f2f535b
--- /dev/null
+++ b/bootloaders/uart/uart_binary.c
@@ -0,0 +1,65 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include "pico/stdlib.h"
+#include "hardware/uart.h"
+#include "hardware/structs/pads_qspi.h"
+#include "hardware/structs/io_qspi.h"
+
+#ifndef LED_DELAY_MS
+#define LED_DELAY_MS 500
+#endif
+
+// Initialize the GPIO for the LED
+void pico_led_init(void) {
+#ifdef PICO_DEFAULT_LED_PIN
+    // A device like Pico that uses a GPIO for the LED will define PICO_DEFAULT_LED_PIN
+    // so we can use normal GPIO functionality to turn the led on and off
+    gpio_init(PICO_DEFAULT_LED_PIN);
+    gpio_set_dir(PICO_DEFAULT_LED_PIN, GPIO_OUT);
+#endif
+}
+
+// Turn the LED on or off
+void pico_set_led(bool led_on) {
+#if defined(PICO_DEFAULT_LED_PIN)
+    // Just set the GPIO on or off
+    gpio_put(PICO_DEFAULT_LED_PIN, led_on);
+#endif
+}
+
+// Set function for QSPI GPIO pin
+void qspi_gpio_set_function(uint gpio, gpio_function_t fn) {
+    // Set input enable on, output disable off
+    hw_write_masked(&pads_qspi_hw->io[gpio],
+                   PADS_QSPI_GPIO_QSPI_SD2_IE_BITS,
+                   PADS_QSPI_GPIO_QSPI_SD2_IE_BITS | PADS_QSPI_GPIO_QSPI_SD2_OD_BITS
+    );
+    // Zero all fields apart from fsel; we want this IO to do what the peripheral tells it.
+    // This doesn't affect e.g. pullup/pulldown, as these are in pad controls.
+    io_qspi_hw->io[gpio].ctrl = fn << IO_QSPI_GPIO_QSPI_SD2_CTRL_FUNCSEL_LSB;
+
+    // Remove pad isolation now that the correct peripheral is in control of the pad
+    hw_clear_bits(&pads_qspi_hw->io[gpio], PADS_QSPI_GPIO_QSPI_SD2_ISO_BITS);
+}
+
+int main() {
+    pico_led_init();
+
+    // SD2 is QSPI GPIO 3, SD3 is QSPI GPIO 4
+    qspi_gpio_set_function(3, GPIO_FUNC_UART_AUX);
+    qspi_gpio_set_function(4, GPIO_FUNC_UART_AUX);
+
+    uart_init(uart0, 1000000);
+
+    while (true) {
+        uart_puts(uart0, "Hello, world\n");
+        pico_set_led(true);
+        sleep_ms(LED_DELAY_MS);
+        pico_set_led(false);
+        sleep_ms(LED_DELAY_MS);
+    }
+}
diff --git a/bootloaders/uart/uart_boot.c b/bootloaders/uart/uart_boot.c
new file mode 100644
index 000000000..caeed6113
--- /dev/null
+++ b/bootloaders/uart/uart_boot.c
@@ -0,0 +1,152 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "pico/stdlib.h"
+#include "hardware/uart.h"
+#include "pico/bootrom.h"
+#include "boot/picobin.h"
+#include "hardware/flash.h"
+
+// UART defines for uart boot
+#define UART_ID uart1
+#define BAUD_RATE 1000000
+
+// Use pins 4 and 5 for uart boot
+#define UART_TX_PIN 4
+#define UART_RX_PIN 5
+
+// Use pin 3 for the RUN pin on the other chip
+#define RUN_PIN 3
+
+
+void reset_chip() {
+    // Toggle run pin
+    gpio_put(RUN_PIN, false);
+    sleep_ms(1);
+    gpio_put(RUN_PIN, true);
+}
+
+
+void uart_boot() {
+    uint knocks = 0;
+    while (true) {
+        // Send the knock sequence
+        uart_putc_raw(UART_ID, 0x56);
+        uart_putc_raw(UART_ID, 0xff);
+        uart_putc_raw(UART_ID, 0x8b);
+        uart_putc_raw(UART_ID, 0xe4);
+        uart_putc_raw(UART_ID, 'n');
+
+        if (uart_is_readable_within_us(UART_ID, 1000)) {
+            char in = uart_getc(UART_ID);
+            printf("%c\n", in);
+            break;
+        } else {
+            if (knocks > 10) {
+                printf("No response - resetting\n");    
+                reset_chip();
+                return;
+            }
+            printf("No response - knocking again\n");
+            knocks++;
+        }
+    }
+
+    printf("Boot starting\n");
+
+    // Get partition location in flash
+    const int buf_words = (16 * 4) + 1;   // maximum of 16 partitions, each with maximum of 4 words returned, plus 1
+    uint32_t* buffer = malloc(buf_words * 4);
+
+    int ret = rom_get_partition_table_info(buffer, buf_words, PT_INFO_PARTITION_LOCATION_AND_FLAGS | PT_INFO_SINGLE_PARTITION | (0 << 24));
+    assert(buffer[0] == (PT_INFO_PARTITION_LOCATION_AND_FLAGS | PT_INFO_SINGLE_PARTITION));
+    assert(ret == 3);
+
+    uint32_t location_and_permissions = buffer[1];
+    uint32_t saddr = XIP_BASE + ((location_and_permissions >> PICOBIN_PARTITION_LOCATION_FIRST_SECTOR_LSB) & 0x1fffu) * FLASH_SECTOR_SIZE;
+    uint32_t eaddr = XIP_BASE + (((location_and_permissions >> PICOBIN_PARTITION_LOCATION_LAST_SECTOR_LSB) & 0x1fffu) + 1) * FLASH_SECTOR_SIZE;
+    printf("Start %08x, end %08x\n", saddr, eaddr);
+
+    free(buffer);
+
+    printf("Writing binary\n");
+    uint32_t tstart = time_us_32();
+    uint32_t caddr = saddr;
+    while (caddr < eaddr) {
+        uart_putc_raw(UART_ID, 'w');
+        char *buf = (char*)caddr;
+        for (int i=0; i < 32; i++) {
+            uart_putc_raw(UART_ID, buf[i]);
+        }
+        if (!uart_is_readable_within_us(UART_ID, 500)) {
+            // Detect hangs and reset the chip
+            printf("Write has hung - resetting\n");
+            reset_chip();
+            return;
+        }
+        char in = uart_getc(UART_ID);
+        printf("%c\n", in);
+        caddr += 32;
+    }
+
+    uint32_t tend = time_us_32();
+    printf("Write took %dus\n", tend - tstart);
+    printf("Write complete - executing\n");
+    uart_putc_raw(UART_ID, 'x');
+    if (!uart_is_readable_within_us(UART_ID, 500)) {
+        // Detect hangs and reset the chip
+        printf("Execute has hung - resetting\n");
+        reset_chip();
+        return;
+    }
+    char in = uart_getc(UART_ID);
+    printf("%c\n", in);
+}
+
+
+int main()
+{
+    stdio_init_all();
+
+    // Set up our UART for booting the other device
+    uart_init(UART_ID, BAUD_RATE);
+    gpio_set_function(UART_TX_PIN, GPIO_FUNC_UART);
+    gpio_set_function(UART_RX_PIN, GPIO_FUNC_UART);
+
+    // Set up run pin
+    gpio_init(RUN_PIN);
+    gpio_set_dir(RUN_PIN, GPIO_OUT);
+
+    // Reset chip
+    reset_chip();
+
+
+    while (true) {
+        char splash[] = "RP2350";
+        char hello[] = "Hello";
+        char buf[500] = {0};
+        int i = 0;
+        while (uart_is_readable(UART_ID) && i < sizeof(buf)) {
+            char in = uart_getc(UART_ID);
+            printf("%c", in);
+            buf[i] = in;
+            i++;
+        }
+        if (i > 0) {
+            printf(" ...Read done\n");
+        }
+        char *ptr = memchr(buf, 'R', sizeof(buf));
+        if (ptr && strncmp(ptr, splash, sizeof(splash) - 1) == 0) {
+            printf("Splash found\n");
+            uart_boot();
+        } else {
+            ptr = memchr(buf, 'H', sizeof(buf));
+            if (ptr && strncmp(ptr, hello, sizeof(hello) - 1) == 0) {
+                printf("Device is running\n");
+            } else {
+                printf("Device not running - attempting reset\n");
+                reset_chip();
+            }
+        }
+        sleep_ms(1000);
+    }
+}

From d323d12fdf9cf7169df208e366468b3a7e46c3ff Mon Sep 17 00:00:00 2001
From: William Vinnicombe <william.vinnicombe@raspberrypi.com>
Date: Thu, 14 Nov 2024 17:10:56 +0000
Subject: [PATCH 2/5] Hardcode baud rate, as it's fixed by the bootrom

---
 bootloaders/uart/uart_boot.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/bootloaders/uart/uart_boot.c b/bootloaders/uart/uart_boot.c
index caeed6113..186bddd9f 100644
--- a/bootloaders/uart/uart_boot.c
+++ b/bootloaders/uart/uart_boot.c
@@ -8,7 +8,6 @@
 
 // UART defines for uart boot
 #define UART_ID uart1
-#define BAUD_RATE 1000000
 
 // Use pins 4 and 5 for uart boot
 #define UART_TX_PIN 4
@@ -108,7 +107,7 @@ int main()
     stdio_init_all();
 
     // Set up our UART for booting the other device
-    uart_init(UART_ID, BAUD_RATE);
+    uart_init(UART_ID, 1000000);
     gpio_set_function(UART_TX_PIN, GPIO_FUNC_UART);
     gpio_set_function(UART_RX_PIN, GPIO_FUNC_UART);
 

From a30a1406a2bfa7d8e8bd34bec790abf35155da57 Mon Sep 17 00:00:00 2001
From: William Vinnicombe <william.vinnicombe@raspberrypi.com>
Date: Fri, 15 Nov 2024 13:29:10 +0000
Subject: [PATCH 3/5] Tidy up variable names, add assets on correct chars, and
 improve documentation

---
 README.md                       |  3 +++
 bootloaders/uart/CMakeLists.txt |  6 ++++++
 bootloaders/uart/uart_boot.c    | 27 +++++++++++++++------------
 3 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/README.md b/README.md
index cbdfaff48..282944f55 100644
--- a/README.md
+++ b/README.md
@@ -52,6 +52,9 @@ App|Description
 [hello_anything](binary_info/hello_anything) | Uses `bi_ptr` variables to create a configurable hello_world binary - see the separate [README](binary_info/README.md) for more details
 
 ### Bootloaders (RP235x Only)
+
+These examples all produce multiple UF2s - a bootloader UF2, and then a separate UF2 of the program that the bootloader will load and boot. To load them onto a device with empty flash, first load the bootloader UF2, then reset to BOOTSEL mode and load the program UF2. This ordering is required because the bootloaders contain embedded partition tables - see section 5.10.6 in the RP2350 datasheet for more details on those.
+
 App|Description
 ---|---
 [enc_bootloader](bootloaders/encrypted) | A bootloader which decrypts binaries from flash into SRAM. See the separate [README](bootloaders/encrypted/README.md) for more information
diff --git a/bootloaders/uart/CMakeLists.txt b/bootloaders/uart/CMakeLists.txt
index cc0e38caa..6c9561f12 100644
--- a/bootloaders/uart/CMakeLists.txt
+++ b/bootloaders/uart/CMakeLists.txt
@@ -5,7 +5,10 @@ add_executable(uart_boot
 # pull in common dependencies
 target_link_libraries(uart_boot pico_stdlib hardware_flash)
 
+# add partition table
 pico_embed_pt_in_binary(uart_boot ${CMAKE_CURRENT_LIST_DIR}/uart-pt.json)
+
+# create absolute UF2
 pico_set_uf2_family(uart_boot "absolute")
 
 # create map/bin/hex file etc.
@@ -15,6 +18,7 @@ pico_add_extra_outputs(uart_boot)
 example_auto_set_url(uart_boot)
 
 
+# Create separate binary to be loaded onto other device
 add_executable(uart_binary
     uart_binary.c
     )
@@ -23,6 +27,8 @@ add_executable(uart_binary
 target_link_libraries(uart_binary pico_stdlib)
 
 pico_set_binary_type(uart_binary no_flash)
+
+# package uf2 in flash
 pico_package_uf2_output(uart_binary 0x10000000)
 
 # create map/bin/hex/uf2 file etc.
diff --git a/bootloaders/uart/uart_boot.c b/bootloaders/uart/uart_boot.c
index 186bddd9f..97c72e95f 100644
--- a/bootloaders/uart/uart_boot.c
+++ b/bootloaders/uart/uart_boot.c
@@ -37,6 +37,7 @@ void uart_boot() {
 
         if (uart_is_readable_within_us(UART_ID, 1000)) {
             char in = uart_getc(UART_ID);
+            assert(in == 'n');
             printf("%c\n", in);
             break;
         } else {
@@ -61,18 +62,18 @@ void uart_boot() {
     assert(ret == 3);
 
     uint32_t location_and_permissions = buffer[1];
-    uint32_t saddr = XIP_BASE + ((location_and_permissions >> PICOBIN_PARTITION_LOCATION_FIRST_SECTOR_LSB) & 0x1fffu) * FLASH_SECTOR_SIZE;
-    uint32_t eaddr = XIP_BASE + (((location_and_permissions >> PICOBIN_PARTITION_LOCATION_LAST_SECTOR_LSB) & 0x1fffu) + 1) * FLASH_SECTOR_SIZE;
-    printf("Start %08x, end %08x\n", saddr, eaddr);
+    uint32_t start_addr = XIP_BASE + ((location_and_permissions & PICOBIN_PARTITION_LOCATION_FIRST_SECTOR_BITS) >> PICOBIN_PARTITION_LOCATION_FIRST_SECTOR_LSB) * FLASH_SECTOR_SIZE;
+    uint32_t end_addr = XIP_BASE + (((location_and_permissions & PICOBIN_PARTITION_LOCATION_LAST_SECTOR_BITS) >> PICOBIN_PARTITION_LOCATION_LAST_SECTOR_LSB) + 1) * FLASH_SECTOR_SIZE;
+    printf("Start %08x, end %08x\n", start_addr, end_addr);
 
     free(buffer);
 
     printf("Writing binary\n");
-    uint32_t tstart = time_us_32();
-    uint32_t caddr = saddr;
-    while (caddr < eaddr) {
+    uint32_t time_start = time_us_32();
+    uint32_t current_addr = start_addr;
+    while (current_addr < end_addr) {
         uart_putc_raw(UART_ID, 'w');
-        char *buf = (char*)caddr;
+        char *buf = (char*)current_addr;
         for (int i=0; i < 32; i++) {
             uart_putc_raw(UART_ID, buf[i]);
         }
@@ -84,11 +85,12 @@ void uart_boot() {
         }
         char in = uart_getc(UART_ID);
         printf("%c\n", in);
-        caddr += 32;
+        assert(in == 'w');
+        current_addr += 32;
     }
 
-    uint32_t tend = time_us_32();
-    printf("Write took %dus\n", tend - tstart);
+    uint32_t time_end = time_us_32();
+    printf("Write took %dus\n", time_end - time_start);
     printf("Write complete - executing\n");
     uart_putc_raw(UART_ID, 'x');
     if (!uart_is_readable_within_us(UART_ID, 500)) {
@@ -99,6 +101,7 @@ void uart_boot() {
     }
     char in = uart_getc(UART_ID);
     printf("%c\n", in);
+    assert(in == 'x');
 }
 
 
@@ -133,12 +136,12 @@ int main()
         if (i > 0) {
             printf(" ...Read done\n");
         }
-        char *ptr = memchr(buf, 'R', sizeof(buf));
+        char *ptr = memchr(buf, splash[0], sizeof(buf));
         if (ptr && strncmp(ptr, splash, sizeof(splash) - 1) == 0) {
             printf("Splash found\n");
             uart_boot();
         } else {
-            ptr = memchr(buf, 'H', sizeof(buf));
+            ptr = memchr(buf, hello[0], sizeof(buf));
             if (ptr && strncmp(ptr, hello, sizeof(hello) - 1) == 0) {
                 printf("Device is running\n");
             } else {

From d1819cc8ef3c9984c6d73812a94b86f7fbcf91b0 Mon Sep 17 00:00:00 2001
From: William Vinnicombe <william.vinnicombe@raspberrypi.com>
Date: Fri, 15 Nov 2024 14:25:11 +0000
Subject: [PATCH 4/5] Add verify, support Risc-V, and replace asserts on
 returned chars with reset_chips

---
 bootloaders/uart/uart-pt.json |  4 +-
 bootloaders/uart/uart_boot.c  | 82 +++++++++++++++++++++++++++++++----
 2 files changed, 75 insertions(+), 11 deletions(-)

diff --git a/bootloaders/uart/uart-pt.json b/bootloaders/uart/uart-pt.json
index d6ce01299..c42cc1098 100644
--- a/bootloaders/uart/uart-pt.json
+++ b/bootloaders/uart/uart-pt.json
@@ -12,7 +12,7 @@
     {
       "start": "128K",
       "size": "32K",
-      "families": ["rp2350-arm-s"],
+      "families": ["rp2350-arm-s", "rp2350-riscv"],
       "permissions": {
         "secure": "rw",
         "nonsecure": "rw",
@@ -20,4 +20,4 @@
       }
     }
   ]
-}
\ No newline at end of file
+}
diff --git a/bootloaders/uart/uart_boot.c b/bootloaders/uart/uart_boot.c
index 97c72e95f..120f712de 100644
--- a/bootloaders/uart/uart_boot.c
+++ b/bootloaders/uart/uart_boot.c
@@ -27,6 +27,7 @@ void reset_chip() {
 
 void uart_boot() {
     uint knocks = 0;
+    char in = 0;
     while (true) {
         // Send the knock sequence
         uart_putc_raw(UART_ID, 0x56);
@@ -36,13 +37,17 @@ void uart_boot() {
         uart_putc_raw(UART_ID, 'n');
 
         if (uart_is_readable_within_us(UART_ID, 1000)) {
-            char in = uart_getc(UART_ID);
-            assert(in == 'n');
+            in = uart_getc(UART_ID);
+            if (in != 'n') {
+                printf("Incorrect response - resetting\n");
+                reset_chip();
+                return;
+            }
             printf("%c\n", in);
             break;
         } else {
             if (knocks > 10) {
-                printf("No response - resetting\n");    
+                printf("No response - resetting\n");
                 reset_chip();
                 return;
             }
@@ -83,15 +88,70 @@ void uart_boot() {
             reset_chip();
             return;
         }
-        char in = uart_getc(UART_ID);
-        printf("%c\n", in);
-        assert(in == 'w');
+        in = uart_getc(UART_ID);
+        if (in != 'w') {
+            printf("Incorrect response - resetting\n");
+            reset_chip();
+            return;
+        }
         current_addr += 32;
     }
 
     uint32_t time_end = time_us_32();
     printf("Write took %dus\n", time_end - time_start);
-    printf("Write complete - executing\n");
+    printf("Write complete - resetting pointer\n");
+
+    uart_putc_raw(UART_ID, 'c');
+    if (!uart_is_readable_within_us(UART_ID, 500)) {
+        // Detect hangs and reset the chip
+        printf("Clear has hung - resetting\n");
+        reset_chip();
+        return;
+    }
+    in = uart_getc(UART_ID);
+    printf("%c\n", in);
+    if (in != 'c') {
+        printf("Incorrect response - resetting\n");
+        reset_chip();
+        return;
+    }
+
+    printf("Verifying binary\n");
+    time_start = time_us_32();
+    current_addr = start_addr;
+    while (current_addr < end_addr) {
+        uart_putc_raw(UART_ID, 'r');
+        char *buf = (char*)current_addr;
+        if (!uart_is_readable_within_us(UART_ID, 500)) {
+            // Detect hangs and reset the chip
+            printf("Verify has hung - resetting\n");
+            reset_chip();
+            return;
+        }
+        int i = 0;
+        while (uart_is_readable_within_us(UART_ID, 10) && i < 32) {
+            in = uart_getc(UART_ID);
+            if (in != buf[i]) {
+                printf("Verify has incorrect data at 0x%08x - resetting\n", current_addr - start_addr + SRAM_BASE);
+            }
+            i++;
+        }
+        if (i != 32) {
+            printf("Verify has incorrect data size - resetting\n");
+        }
+        in = uart_getc(UART_ID);
+        if (in != 'r') {
+            printf("Incorrect response - resetting\n");
+            reset_chip();
+            return;
+        }
+        current_addr += 32;
+    }
+
+    time_end = time_us_32();
+    printf("Verify took %dus\n", time_end - time_start);
+    printf("Verify complete - executing\n");
+
     uart_putc_raw(UART_ID, 'x');
     if (!uart_is_readable_within_us(UART_ID, 500)) {
         // Detect hangs and reset the chip
@@ -99,9 +159,13 @@ void uart_boot() {
         reset_chip();
         return;
     }
-    char in = uart_getc(UART_ID);
+    in = uart_getc(UART_ID);
     printf("%c\n", in);
-    assert(in == 'x');
+    if (in != 'x') {
+        printf("Incorrect response - resetting\n");
+        reset_chip();
+        return;
+    }
 }
 
 

From d7170caf56b529c4c048dfb786a8b149694883a6 Mon Sep 17 00:00:00 2001
From: William Vinnicombe <william.vinnicombe@raspberrypi.com>
Date: Tue, 15 Apr 2025 18:03:39 +0100
Subject: [PATCH 5/5] Add note as to why bootloader should be absolute

---
 bootloaders/uart/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bootloaders/uart/CMakeLists.txt b/bootloaders/uart/CMakeLists.txt
index 6c9561f12..d14109b57 100644
--- a/bootloaders/uart/CMakeLists.txt
+++ b/bootloaders/uart/CMakeLists.txt
@@ -8,7 +8,7 @@ target_link_libraries(uart_boot pico_stdlib hardware_flash)
 # add partition table
 pico_embed_pt_in_binary(uart_boot ${CMAKE_CURRENT_LIST_DIR}/uart-pt.json)
 
-# create absolute UF2
+# create absolute UF2, as it's a bootloader so shouldn't go in a partition
 pico_set_uf2_family(uart_boot "absolute")
 
 # create map/bin/hex file etc.