Add simple UART bootloader example #571
Conversation
bootloaders/uart/uart_boot.c
Outdated
| #define UART_ID uart1 | ||
| #define BAUD_RATE 1000000 |
There was a problem hiding this comment.
The baud-rate is hardcoded in uart_binary.c (because I assume that it can't be changed, as it's the baud-rate required by the bootrom) so should it also be hardcoded (rather than being a #define) in uart_boot.c too?
Although I guess that the uart-bootloader baud rate could theoretically be different to the post-boot application baud rate (IYSWIM); so I wonder if having them deliberately different might make this a more interesting example? 🤔
There was a problem hiding this comment.
Yes, it should be hardcoded in both - I've fixed that
If the post-boot application used a different baud rate, then it wouldn't be able to boot the board again if it's power cycled - this way you can power cycle the separate device and watch the bootloader run again without rebooting the main device
There was a problem hiding this comment.
Yeah, I was assuming that in order to accommodate my suggestion, the code (in the main device) would need to dynamically reconfigure the baud rate at the start and end of the uart-boot sequence 🙂
|
I wonder if things like the "splash string", the "knock sequence", the "uart-bootloader baudrate", etc. ought to be defined in a header-file somewhere in EDIT: Ah, perhaps https://github.com/raspberrypi/pico-sdk/blob/develop/src/rp2_common/boot_bootrom_headers/include/boot/bootrom_constants.h would be a good place for those 🙂 |
| reset_chip(); | ||
| return; | ||
| } | ||
| current_addr += 32; |
There was a problem hiding this comment.
Or I guess you could do += i 😉
| printf("Splash found\n"); | ||
| uart_boot(); | ||
| } else { | ||
| ptr = memchr(buf, hello[0], sizeof(buf)); |
There was a problem hiding this comment.
Hah, I guess it's important that hello[0] doesn't appear anywhere in the splash string 😉
Is there any reason not to have this check for the full "Hello, world\n" that uart_binary transmits?
| char splash[] = "RP2350"; | ||
| char hello[] = "Hello"; |
There was a problem hiding this comment.
minor nitpick: I guess these two variables could be moved outside of the while (true) loop?
| #include "hardware/structs/io_qspi.h" | ||
|
|
||
| #ifndef LED_DELAY_MS | ||
| #define LED_DELAY_MS 500 |
There was a problem hiding this comment.
From what I understand, I think the "parent" RP2350 will reset the "child" RP2350 if it doesn't receive the string "Hello" once per second; so I guess that means that LED_DELAY_MS can't be larger than 500?
|
This worked well for me once I'd figured out that the uart binary had to be loaded into the "master" device first. It would be more fun if the binary could be built into a header file to avoid that step |
bootloaders/uart/CMakeLists.txt
Outdated
| # add partition table | ||
| pico_embed_pt_in_binary(uart_boot ${CMAKE_CURRENT_LIST_DIR}/uart-pt.json) | ||
|
|
||
| # create absolute UF2 |
There was a problem hiding this comment.
possible worth a quick why comment
There was a problem hiding this comment.
Added - it's because it's a bootloader, so shouldn't go in a partition
The sample binary flashes the LED and prints Hello, world back over the UART interface
Add a UART bootloader example, which reads a binary from the partition table on the main device, and uses the UART bootloader to boot that binary on a separate device. Requires a modified separate board to run, as you need access to the QSPI pins to use them as UARTs for the bootloader (see 5.8 in the datasheet) - the main board can be a normal RP2350 board.
This sample binary flashes the LED and prints "Hello, world" back over the UART interface, which demonstrates setting up QSPI GPIOs as UARTs.