5 ymodem_ota接收数据大小问题

发布于 2020-12-03 13:23:47 浏览：1471 订阅该版

- rt-thread 3.1.4
- stm32f4
- ymodem和ymodem_ota
    ymodem.c中函数
```c
static rt_err_t _rym_trans_data(
    struct rym_ctx *ctx,
    rt_size_t data_sz,
    enum rym_code *code)
{
    const rt_size_t tsz = 2 + data_sz + 2;
    rt_uint16_t recv_crc;

/* seq + data + crc */
    rt_size_t i = _rym_read_data(ctx, tsz);
    if (i != tsz)
        return -RYM_ERR_DSZ;

if ((ctx->buf[1] + ctx->buf[2]) != 0xFF)
    {
        return -RYM_ERR_SEQ;
    }

/* As we are sending C continuously, there is a chance that the
     * sender(remote) receive an C after sending the first handshake package.
     * So the sender will interpret it as NAK and re-send the package. So we
     * just ignore it and proceed. */
    if (ctx->stage == RYM_STAGE_ESTABLISHED && ctx->buf[1] == 0x00)
    {
        *code = RYM_CODE_NONE;
        return RT_EOK;
    }

ctx->stage = RYM_STAGE_TRANSMITTING;

/* sanity check */
    recv_crc = (rt_uint16_t)(*(ctx->buf + tsz - 1) << 8) | *(ctx->buf + tsz);
    if (recv_crc != CRC16(ctx->buf + 3, data_sz))
        return -RYM_ERR_CRC;

/* congratulations, check passed. */
    if (ctx->on_data)
        *code = ctx->on_data(ctx, ctx->buf + 3, data_sz);
    else
        *code = RYM_CODE_ACK;
    return RT_EOK;
}
```
其中rt_size_t data_sz是ymodmem的数据段最大长度，128或1024，在回调函数用到
    /* congratulations, check passed. */
    if (ctx->on_data)
        *code = ctx->on_data(ctx, ctx->buf + 3, data_sz);
实际这个data_sz也是128或1024.

ymodem_ota.c中此回调函数具体为
```c
static enum rym_code ymodem_on_data(struct rym_ctx *ctx, rt_uint8_t *buf, rt_size_t len)
{
    ...
    if (fal_partition_write(dl_part, update_file_cur_size, buf, len) < 0)
    {
        LOG_E("Firmware download failed! Partition (%s) write data error!", dl_part->name);
        return RYM_CODE_CAN;
    }
}
```c
直接用此data_sz作为写flash的长度，为什么是这样做，实际用xshell发送226796字节，而以上data_sz的累加会为226816字节（恰好是128*1772），这个写文件不会多出20个字节么？
![data_send.jpg](/uploads/20201203/1366ccd5e9471c9e04c280dccb9954f6.jpg)
![bytes_received.png](/uploads/20201203/4dd0c006cf2068e7655962e713bd8608.png)