Initial

.gitignore

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+tmp
+*.sw?

README.md

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+# USB Flashing Format (UF2)
+
+UF2 (USB Flashing Format) is a name of a file format, that is particularly
+suitable for flashing devices over MSC (Mass Storage Class most commonly used
+by various pendrives) The file consists of 512 byte blocks, each of which is
+self-contained and independent of others.
+
+Each 512 byte block consist of (see `uf2.h` for details):
+* magic numbers at the beginning and at the end
+* address where the data should be flashed
+* size of data
+* data (up to 476 bytes; for SAMD it's 256 bytes so it's easy to flash in one go)
+
+Thus, it's really easy for the microcontroller to recognize a block of
+a UF2 file is written and immediately write it to flash.
+
+In `uf2conv.c` you can find a small converter from `.bin` to `.uf2`.
+
+## Board identification
+
+There is also `BOARD_ID`, which is meant to be machine-readable and specific
+to a given version of board hardware. The programming environment might use
+this to suggest packages to be imported (i.e., a package for a particular
+external flash chip, SD card etc.).
+
+These configuration values can be read from `INFO_UF2.TXT` file.
+Presence of this file can be tested to see if the board supports `UF2` flashing,
+while contest, particularly `Board-ID` field, can be used for feature detection.
+
+The current flash contents of the board is exposed as `CURRENT.UF2` file.
+This file includes the bootloader address space. The last word of bootloader
+space points to the string holding the `INFO_UF2.TXT` file, so it can be parsed
+by a programming environment to determine which board does the `.UF2` file comes from.
+
+## License
+
+MIT

uf2.h

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+#ifndef UF2FORMAT_H
+#define UF2FORMAT_H 1
+
+#include <stdint.h>
+#include <stdbool.h>
+
+// All entries are little endian.
+
+#define UF2_MAGIC_START0 0x0A324655UL // "UF2\n"
+#define UF2_MAGIC_START1 0x9E5D5157UL // Randomly selected
+#define UF2_MAGIC_END 0x0AB16F30UL    // Ditto
+
+// If set, the block is "comment" and should not be flashed to the device
+#define UF2_FLAG_NOFLASH 0x00000001
+
+typedef struct {
+    // 32 byte header
+    uint32_t magicStart0;
+    uint32_t magicStart1;
+    uint32_t flags;
+    uint32_t targetAddr;
+    uint32_t payloadSize;
+    uint32_t blockNo;
+    uint32_t numBlocks;
+    uint32_t reserved;
+
+    // raw data;
+    uint8_t data[476];
+
+    // store magic also at the end to limit damage from partial block reads
+    uint32_t magicEnd;
+} UF2_Block;
+
+#endif

utils/uf2conv.c

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+#include <stdio.h>
+#include <string.h>
+#include "uf2format.h"
+
+int main(int argc, char **argv) {
+    if (argc < 2) {
+        fprintf(stderr, "USAGE: %s file.bin [file.uf2]\n", argv[0]);
+        return 1;
+    }
+    FILE *f = fopen(argv[1], "rb");
+    if (!f) {
+        fprintf(stderr, "No such file: %s\n", argv[1]);
+        return 1;
+    }
+
+    fseek(f, 0L, SEEK_END);
+    uint32_t sz = ftell(f);
+    fseek(f, 0L, SEEK_SET);
+
+    const char *outname = argc > 2 ? argv[2] : "flash.uf2";
+
+    FILE *fout = fopen(outname, "wb");
+
+    UF2_Block bl;
+    memset(&bl, 0, sizeof(bl));
+
+    bl.magicStart0 = UF2_MAGIC_START0;
+    bl.magicStart1 = UF2_MAGIC_START1;
+    bl.magicEnd = UF2_MAGIC_END;
+    bl.targetAddr = APP_START_ADDRESS;
+    bl.numBlocks = (sz + 255) / 256;
+    bl.payloadSize = 256;
+    int numbl = 0;
+    while (fread(bl.data, 1, bl.payloadSize, f)) {
+        bl.blockNo = numbl++;
+        fwrite(&bl, 1, sizeof(bl), fout);
+        bl.targetAddr += bl.payloadSize;
+        // clear for next iteration, in case we get a short read
+        memset(bl.data, 0, sizeof(bl.data));
+    }
+    fclose(fout);
+    fclose(f);
+    printf("Wrote %d blocks to %s\n", numbl, outname);
+    return 0;
+}