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ymodem: fix a race-condition in handshaking 

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.
This commit is contained in:
Grissiom 2014-12-26 22:20:17 +08:00
parent 188b64203b
commit d479960aac
2 changed files with 14 additions and 2 deletions
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13
components/utilities/ymodem/ymodem.c
View File

@ -174,6 +174,18 @@ static rt_err_t _rym_trans_data(
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))
@ -214,7 +226,6 @@ static rt_err_t _rym_do_trans(struct rym_ctx *ctx)
default:
return -RYM_ERR_CODE;
};
ctx->stage = RYM_STAGE_TRANSMITTING;
err = _rym_trans_data(ctx, data_sz, &code);
if (err != RT_EOK)

3
components/utilities/ymodem/ymodem.h
View File

@ -66,7 +66,8 @@ enum rym_stage {
RYM_STAGE_ESTABLISHING,
/* set when we've got the packet 0 and sent ACK and second C */
RYM_STAGE_ESTABLISHED,
/* set when the sender respond to our second C */
/* set when the sender respond to our second C and recviever got a real
* data packet. */
RYM_STAGE_TRANSMITTING,
/* set when the sender send a EOT */
RYM_STAGE_FINISHING,