General • Re: Pico minimal 2nd stage boot loader

Code:

#include <stdio.h>#include <string.h>#include <stdint.h>#define APP_START_ADDRESS 0x10000000#define UF2_MAGIC_START0 0x0A324655UL // "UF2\n"#define UF2_MAGIC_START1 0x9E5D5157UL // Randomly selected#define UF2_MAGIC_END 0x0AB16F30UL    // Ditto#define UF2_FLAG_FAMILY_ID      0x00002000  // familyID present#define UF2_PICO_FAMILY_ID      0xE48BFF56  // Raspberry PICO family ID#pragma pack(1)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;#pragma pack()unsigned int crc32b(uint8_t* message, size_t l){    size_t i, j;    unsigned int crc, msb;    crc = 0xFFFFFFFF;    for (i = 0; i < l; i++) {        // xor next byte to upper bits of crc        crc ^= (((unsigned int)message[i]) << 24);        for (j = 0; j < 8; j++) {    // Do eight times.            msb = crc >> 31;            crc <<= 1;            crc ^= (0 - msb) & 0x04C11DB7;        }    }    return crc;}int main(int argc, char **argv) {    UF2_Block bl = { 0 };        FILE* f = fopen(argv[1], "rb");    if (!f) {        fprintf(stderr, "No such bootloader input file\n");        return 1;    }    fseek(f, 0L, SEEK_END);    int32_t tsz = ftell(f);    fseek(f, 0L, SEEK_SET);    if (tsz > 252) {        fprintf(stderr, "Boot loader can only be 252 bytes max\n");        return 1;    }    fread(&bl.data[0], 1, 256, f);    uint32_t crc = crc32b(&bl.data[0], 252);    bl.data[255] = ((crc & 0xFF000000) >> 24);    bl.data[254] = ((crc & 0x00FF0000) >> 16);    bl.data[253] = ((crc & 0x0000FF00) >> 8);    bl.data[252] = ((crc & 0x000000FF));    FILE* fa = fopen(argv[2], "rb");    if (!fa) {        fprintf(stderr, "No such app input file\n");        return 1;    }    fseek(fa, 0L, SEEK_END);    int32_t sz = ftell(fa);    fseek(fa, 0L, SEEK_SET);    FILE* fout = fopen(argv[3], "wb");    if (!fout) {        fprintf(stderr, "Output file create failed\n");        return 1;    }    bl.magicStart0 = UF2_MAGIC_START0;    bl.magicStart1 = UF2_MAGIC_START1;    bl.magicEnd = UF2_MAGIC_END;    bl.targetAddr = APP_START_ADDRESS;    bl.flags = UF2_FLAG_FAMILY_ID;    bl.reserved = UF2_PICO_FAMILY_ID;    bl.blockNo = 0;    bl.numBlocks = (tsz + sz + 255) / 256;    bl.payloadSize = 256;    fwrite(&bl, 1, sizeof(bl), fout);    while (sz > 0)    {        uint32_t rem = sz;        if (rem > 256) rem = 256;        memset(&bl.data[0], 256, 0);        bl.targetAddr = bl.targetAddr + 256;        bl.blockNo = bl.blockNo + 1;        fread(&bl.data[0], 1, rem, fa);        fwrite(&bl, 1, sizeof(bl), fout);        sz = sz - rem;    }    fclose(f);    fclose(fa);    fclose(fout);    return 0;}