components/utilities: add ymodem

Real-YModem implemented a flexible YModem support. It use callback-based
structure to let the user application to deal with the data. It contains
3 examples:

    1. echo.c: write the data recieved on YModem to an other device
    2. null.c: discard the YModem data
    3. tofile.c: write the data to the file system

Currently, it does not support batch file transmission.

components/utilities/ymodem/SConscript

+from building import *
+
+cwd     = GetCurrentDir()
+src     = Glob('*.c')
+CPPPATH = [cwd]
+group   = DefineGroup('Utilities', src, depend = ['RT_USING_RYM'], CPPPATH = CPPPATH)
+
+Return('group')

components/utilities/ymodem/ymodem.c

+/*
+ * File      : ymodem.c
+ * COPYRIGHT (C) 2012, Shanghai Real-Thread Technology Co., Ltd
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ * 2013-04-14     Grissiom     initial implementation
+ */
+
+#include <rthw.h>
+#include "ymodem.h"
+
+static const rt_uint16_t ccitt_table[256] = {
+    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
+    0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
+    0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
+    0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
+    0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
+    0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
+    0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
+    0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
+    0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
+    0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
+    0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
+    0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
+    0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
+    0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
+    0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
+    0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
+    0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
+    0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
+    0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
+    0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
+    0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
+    0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
+    0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
+    0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
+    0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
+    0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
+    0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
+    0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
+    0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
+    0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
+    0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
+    0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
+};
+rt_uint16_t CRC16(unsigned char *q, int len)
+{
+    rt_uint16_t crc = 0;
+
+    while (len-- > 0)
+        crc = (crc << 8) ^ ccitt_table[((crc >> 8) ^ *q++) & 0xff];
+    return crc;
+}
+
+// we could only use global varible because we could not use
+// rt_device_t->user_data(it is used by the serial driver)...
+static struct rym_ctx *_rym_the_ctx;
+
+static rt_err_t _rym_rx_ind(rt_device_t dev, rt_size_t size)
+{
+    return rt_sem_release(&_rym_the_ctx->sem);
+}
+
+/* SOH/STX + seq + payload + crc */
+#define _RYM_SOH_PKG_SZ (1+2+128+2)
+#define _RYM_STX_PKG_SZ (1+2+1024+2)
+
+static enum rym_code _rym_read_code(
+        struct rym_ctx *ctx,
+        rt_tick_t timeout)
+{
+    /* consume the available sem and read the data in buffer if possible */
+    while (rt_sem_trytake(&ctx->sem) == RT_EOK)
+        ;
+    if (rt_device_read(ctx->dev, 0, ctx->buf, 1) == 1)
+        return *ctx->buf;
+    /* no data yet, wait for one */
+    if (rt_sem_take(&ctx->sem, timeout) != RT_EOK)
+        return RYM_CODE_NONE;
+    /* read one */
+    if (rt_device_read(ctx->dev, 0, ctx->buf, 1) == 1)
+        return *ctx->buf;
+    return RYM_CODE_NONE;
+}
+
+/* the caller should at least alloc _RYM_STX_PKG_SZ buffer */
+static rt_size_t _rym_read_data(
+        struct rym_ctx *ctx,
+        rt_size_t len)
+{
+    /* we should already have had the code */
+    rt_uint8_t *buf = ctx->buf + 1;
+    rt_size_t readlen = 0;
+
+    do
+    {
+        readlen += rt_device_read(ctx->dev,
+                0, buf+readlen, len-readlen);
+        if (readlen >= len)
+            return readlen;
+    } while (rt_sem_take(&ctx->sem, RYM_WAIT_CHR_TICK) == RT_EOK);
+
+    return readlen;
+}
+
+static rt_size_t _rym_putchar(struct rym_ctx *ctx, rt_uint8_t code)
+{
+    rt_device_write(ctx->dev, 0, &code, sizeof(code));
+    return 1;
+}
+
+static rt_err_t _rym_do_handshake(
+        struct rym_ctx *ctx,
+        int tm_sec)
+{
+    enum rym_code code;
+    rt_size_t i;
+    rt_uint16_t recv_crc, cal_crc;
+
+    ctx->stage = RYM_STAGE_ESTABLISHING;
+    /* send C every second, so the sender could know we are waiting for it. */
+    for (i = 0; i < tm_sec; i++)
+    {
+        _rym_putchar(ctx, RYM_CODE_C);
+        code = _rym_read_code(ctx,
+                RYM_CHD_INTV_TICK);
+        if (code == RYM_CODE_SOH)
+            break;
+    }
+    if (i == tm_sec)
+        return -RYM_ERR_TMO;
+
+    i = _rym_read_data(ctx, _RYM_SOH_PKG_SZ-1);
+    if (i != (_RYM_SOH_PKG_SZ-1))
+        return -RYM_ERR_DSZ;
+
+    /* sanity check */
+    if (ctx->buf[1] != 0 || ctx->buf[2] != 0xFF)
+        return -RYM_ERR_SEQ;
+
+    recv_crc = (rt_uint16_t)(*(ctx->buf+_RYM_SOH_PKG_SZ-2) << 8) | *(ctx->buf+_RYM_SOH_PKG_SZ-1);
+    cal_crc = CRC16(ctx->buf+3, _RYM_SOH_PKG_SZ-5);
+    if (recv_crc != cal_crc)
+        return -RYM_ERR_CRC;
+
+    /* congratulations, check passed. */
+    if (ctx->on_begin && ctx->on_begin(ctx, ctx->buf+3, 128) != RYM_CODE_ACK)
+        return -RYM_ERR_CAN;
+
+    return RT_EOK;
+}
+
+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;
+    }
+
+    /* 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;
+}
+
+static rt_err_t _rym_do_trans(struct rym_ctx *ctx)
+{
+    _rym_putchar(ctx, RYM_CODE_ACK);
+    _rym_putchar(ctx, RYM_CODE_C);
+    ctx->stage = RYM_STAGE_ESTABLISHED;
+
+    while (1)
+    {
+        rt_err_t err;
+        enum rym_code code;
+        rt_size_t data_sz;
+
+        code = _rym_read_code(ctx,
+                RYM_WAIT_PKG_TICK);
+        switch (code)
+        {
+        case RYM_CODE_SOH:
+            data_sz = 128;
+            break;
+        case RYM_CODE_STX:
+            data_sz = 1024;
+            break;
+        case RYM_CODE_EOT:
+            return RT_EOK;
+        default:
+            return -RYM_ERR_CODE;
+        };
+        ctx->stage = RYM_STAGE_TRANSMITTING;
+
+        err = _rym_trans_data(ctx, data_sz, &code);
+        if (err != RT_EOK)
+            return err;
+        switch (code)
+        {
+        case RYM_CODE_CAN:
+            /* the spec require multiple CAN */
+            _rym_putchar(ctx, RYM_CODE_CAN);
+            _rym_putchar(ctx, RYM_CODE_CAN);
+            return -RYM_ERR_CAN;
+        case RYM_CODE_ACK:
+            _rym_putchar(ctx, RYM_CODE_ACK);
+            break;
+        default:
+            // wrong code
+            break;
+        };
+    }
+}
+
+static rt_err_t _rym_do_fin(struct rym_ctx *ctx)
+{
+    enum rym_code code;
+    rt_uint16_t recv_crc;
+    rt_size_t i;
+
+    ctx->stage = RYM_STAGE_FINISHING;
+    /* we already got one EOT in the caller. invoke the callback if there is
+     * one. */
+    if (ctx->on_end)
+        ctx->on_end(ctx, ctx->buf+3, 128);
+
+    _rym_putchar(ctx, RYM_CODE_NAK);
+    code = _rym_read_code(ctx, RYM_WAIT_PKG_TICK);
+    if (code != RYM_CODE_EOT)
+        return -RYM_ERR_CODE;
+
+    _rym_putchar(ctx, RYM_CODE_ACK);
+    _rym_putchar(ctx, RYM_CODE_C);
+
+    code = _rym_read_code(ctx, RYM_WAIT_PKG_TICK);
+    if (code != RYM_CODE_SOH)
+        return -RYM_ERR_CODE;
+
+    i = _rym_read_data(ctx, _RYM_SOH_PKG_SZ-1);
+    if (i != (_RYM_SOH_PKG_SZ-1))
+        return -RYM_ERR_DSZ;
+
+    /* sanity check
+     *
+     * TODO: multiple files transmission
+     */
+    if (ctx->buf[1] != 0 || ctx->buf[2] != 0xFF)
+        return -RYM_ERR_SEQ;
+
+    recv_crc = (rt_uint16_t)(*(ctx->buf+_RYM_SOH_PKG_SZ-2) << 8) | *(ctx->buf+_RYM_SOH_PKG_SZ-1);
+    if (recv_crc != CRC16(ctx->buf+3, _RYM_SOH_PKG_SZ-5))
+        return -RYM_ERR_CRC;
+
+    /* congratulations, check passed. */
+    ctx->stage = RYM_STAGE_FINISHED;
+
+    /* put the last ACK */
+    _rym_putchar(ctx, RYM_CODE_ACK);
+
+    return RT_EOK;
+}
+
+static rt_err_t _rym_do_recv(
+        struct rym_ctx *ctx,
+        int handshake_timeout)
+{
+    rt_err_t err;
+
+    ctx->stage = RYM_STAGE_NONE;
+
+    ctx->buf = rt_malloc(_RYM_STX_PKG_SZ);
+    if (ctx->buf == RT_NULL)
+        return -RT_ENOMEM;
+
+    err = _rym_do_handshake(ctx, handshake_timeout);
+    if (err != RT_EOK)
+        return err;
+
+    err = _rym_do_trans(ctx);
+    if (err != RT_EOK)
+        return err;
+
+    return _rym_do_fin(ctx);
+}
+
+rt_err_t rym_recv_on_device(
+        struct rym_ctx *ctx,
+        rt_device_t dev,
+        rym_callback on_begin,
+        rym_callback on_data,
+        rym_callback on_end,
+        int handshake_timeout)
+{
+    rt_err_t res;
+    rt_err_t (*odev_rx_ind)(rt_device_t dev, rt_size_t size);
+    rt_uint16_t odev_flag;
+    int int_lvl;
+
+    RT_ASSERT(_rym_the_ctx == 0);
+    _rym_the_ctx = ctx;
+
+    ctx->on_begin = on_begin;
+    ctx->on_data  = on_data;
+    ctx->on_end   = on_end;
+    ctx->dev      = dev;
+    rt_sem_init(&ctx->sem, "rymsem", 0, RT_IPC_FLAG_FIFO);
+
+    odev_rx_ind = dev->rx_indicate;
+    /* no data should be received before the device has been fully setted up.
+     */
+    int_lvl = rt_hw_interrupt_disable();
+    rt_device_set_rx_indicate(dev, _rym_rx_ind);
+
+    odev_flag = dev->flag;
+    /* make sure the device don't change the content. */
+    dev->flag &= ~RT_DEVICE_FLAG_STREAM;
+    rt_hw_interrupt_enable(int_lvl);
+
+    res = rt_device_open(dev, 0);
+    if (res != RT_EOK)
+        goto __exit;
+
+    res = _rym_do_recv(ctx, handshake_timeout);
+
+    rt_device_close(dev);
+
+__exit:
+    /* no rx_ind should be called before the callback has been fully detached.
+     */
+    int_lvl = rt_hw_interrupt_disable();
+    rt_sem_detach(&ctx->sem);
+
+    dev->flag = odev_flag;
+    rt_device_set_rx_indicate(dev, odev_rx_ind);
+    rt_hw_interrupt_enable(int_lvl);
+
+    rt_free(ctx->buf);
+    _rym_the_ctx = RT_NULL;
+
+    return res;
+}
+

components/utilities/ymodem/ymodem.h

+#ifndef __YMODEM_H__
+#define __YMODEM_H__
+/*
+ * File      : ymodem.h
+ * COPYRIGHT (C) 2012, Shanghai Real-Thread Technology Co., Ltd
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ * 2013-04-14     Grissiom     initial implementation
+ */
+
+#include "rtthread.h"
+
+/* The word "RYM" is stand for "Real-YModem". */
+
+enum rym_code {
+    RYM_CODE_NONE = 0x00,
+    RYM_CODE_SOH  = 0x01,
+    RYM_CODE_STX  = 0x02,
+    RYM_CODE_EOT  = 0x04,
+    RYM_CODE_ACK  = 0x06,
+    RYM_CODE_NAK  = 0x15,
+    RYM_CODE_CAN  = 0x18,
+    RYM_CODE_C    = 0x43,
+};
+
+/* RYM error code
+ *
+ * We use the rt_err_t to return error values. We take use of current error
+ * codes available in RTT and append ourselves.
+ */
+/* timeout on handshake */
+#define RYM_ERR_TMO  0x70
+/* wrong code, wrong SOH, STX etc. */
+#define RYM_ERR_CODE 0x71
+/* wrong sequence number */
+#define RYM_ERR_SEQ  0x72
+/* wrong CRC checksum */
+#define RYM_ERR_CRC  0x73
+/* not enough data received */
+#define RYM_ERR_DSZ  0x74
+/* the transmission is aborted by user */
+#define RYM_ERR_CAN  0x75
+
+/* how many ticks wait for chars between packet. */
+#ifndef RYM_WAIT_CHR_TICK
+#define RYM_WAIT_CHR_TICK (RT_TICK_PER_SECOND * 3)
+#endif
+/* how many ticks wait for between packet. */
+#ifndef RYM_WAIT_PKG_TICK
+#define RYM_WAIT_PKG_TICK (RT_TICK_PER_SECOND * 3)
+#endif
+/* how many ticks between two handshake code. */
+#ifndef RYM_CHD_INTV_TICK
+#define RYM_CHD_INTV_TICK (RT_TICK_PER_SECOND / 4)
+#endif
+
+enum rym_stage {
+    RYM_STAGE_NONE,
+    /* set when C is send */
+    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 */
+    RYM_STAGE_TRANSMITTING,
+    /* set when the sender send a EOT */
+    RYM_STAGE_FINISHING,
+    /* set when transmission is really finished, i.e., after the NAK, C, final
+     * NULL packet stuff. */
+    RYM_STAGE_FINISHED,
+};
+
+struct rym_ctx;
+/* when receiving files, the buf will be the data received from ymodem protocol
+ * and the len is the data size.
+ *
+ * TODO:
+ * When sending files, the len is the buf size in RYM. The callback need to
+ * fill the buf with data to send. Returning RYM_CODE_EOT will terminate the
+ * transfer and the buf will be discarded. Any other return values will cause
+ * the transfer continue.
+ */
+typedef enum rym_code (*rym_callback)(struct rym_ctx *ctx, rt_uint8_t *buf, rt_size_t len);
+
+/* Currently RYM only support one transfer session(ctx) for simplicity.
+ *
+ * In case we could support multiple sessions in The future, the first argument
+ * of APIs are (struct rym_ctx*).
+ */
+struct rym_ctx
+{
+    rym_callback on_data;
+    rym_callback on_begin;
+    rym_callback on_end;
+    /* When error happened, user need to check this to get when the error has
+     * happened. */
+    enum rym_stage stage;
+    /* user could get the error content through this */
+    rt_uint8_t *buf;
+
+    struct rt_semaphore sem;
+
+    rt_device_t dev;
+};
+
+/** recv a file on device dev with ymodem session ctx.
+ *
+ * If an error happens, you can get where it is failed from ctx->stage.
+ *
+ * @param on_begin The callback will be invoked when the first packet arrived.
+ * This packet often contain file names and the size of the file, if the sender
+ * support it. So if you want to save the data to a file, you may need to
+ * create the file on need. It is the on_begin's responsibility to parse the
+ * data content. The on_begin can be NULL, in which case the transmission will
+ * continue without any side-effects.
+ *
+ * @param on_data The callback will be invoked on the packets received.  The
+ * callback should save the data to the destination. The return value will be
+ * sent to the sender and in turn, only RYM_{ACK,CAN} is valid. When on_data is
+ * NULL, RYM will barely send ACK on every packet and have no side-effects.
+ *
+ * @param on_end The callback will be invoked when one transmission is
+ * finished. The data should be 128 bytes of NULL. You can do some cleaning job
+ * in this callback such as closing the file. The return value of this callback
+ * is ignored. As above, this parameter can be NULL if you don't need such
+ * function.
+ *
+ * @param handshake_timeout the timeout when hand shaking. The unit is in
+ * second.
+ */
+rt_err_t rym_recv_on_device(struct rym_ctx *ctx, rt_device_t dev,
+        rym_callback on_begin, rym_callback on_data, rym_callback on_end,
+        int handshake_timeout);
+
+#endif

examples/ymodem/echo.c

+#include <ymodem.h>
+
+static rt_device_t _odev;
+
+static enum rym_code _rym_echo_data(
+        struct rym_ctx *ctx,
+        rt_uint8_t *buf,
+        rt_size_t len)
+{
+    rt_device_write(_odev, 0, buf, len);
+    return RYM_CODE_ACK;
+}
+
+rt_err_t rym_cat_to_dev(rt_device_t idev, rt_device_t odev)
+{
+    struct rym_ctx rctx;
+    rt_err_t res;
+    _odev = odev;
+
+    rt_kprintf("entering RYM mode\n");
+    odev->flag &= ~RT_DEVICE_FLAG_STREAM;
+    res = rt_device_open(odev, 0);
+    if (res != RT_EOK)
+    {
+        rt_kprintf("open output device error: 0x%x", -res);
+        return res;
+    }
+    res = rym_recv_on_device(&rctx, idev,
+            RT_NULL, _rym_echo_data, RT_NULL, 1000);
+    rt_device_close(_odev);
+    rt_kprintf("leaving RYM mode with code %X\n", res);
+    return res;
+}
+
+#ifdef RT_USING_FINSH
+#include <finsh.h>
+void rym_cat_vcom(void)
+{
+    extern rt_err_t rym_cat_to_dev(rt_device_t idev, rt_device_t odev);
+    rt_device_t idev, odev;
+
+    rt_thread_delay(RT_TICK_PER_SECOND*10);
+
+    idev = rt_device_find("uart1");
+    if (!idev)
+    {
+        rt_kprintf("could not find idev\n");
+    }
+    odev = rt_device_find("vcom");
+    if (!odev)
+    {
+        rt_kprintf("could not find odev\n");
+    }
+
+    rym_cat_to_dev(idev, odev);
+}
+FINSH_FUNCTION_EXPORT(rym_cat_vcom, test the YModem);
+#endif
+

examples/ymodem/null.c

+#include <ymodem.h>
+
+static enum rym_code _rym_dummy_write(
+        struct rym_ctx *ctx,
+        rt_uint8_t *buf,
+        rt_size_t len)
+{
+    return RYM_CODE_ACK;
+}
+
+#ifdef RT_USING_FINSH
+#include <finsh.h>
+rt_err_t rym_null(char *devname)
+{
+    struct rym_ctx rctx;
+    rt_device_t dev = rt_device_find(devname);
+    if (!dev)
+    {
+        rt_kprintf("could not find device %s\n", devname);
+        return -1;
+    }
+
+    return rym_recv_on_device(&rctx, dev,
+            RT_NULL, _rym_dummy_write, RT_NULL, 1000);
+}
+FINSH_FUNCTION_EXPORT(rym_null, dump data to null);
+#endif
+

examples/ymodem/tofile.c

+#include <rtthread.h>
+#include <ymodem.h>
+#include <dfs_posix.h>
+#include <stdlib.h>
+
+#include <board.h>
+
+struct custom_ctx
+{
+    struct rym_ctx parent;
+    int fd;
+    int flen;
+    char fpath[256];
+};
+
+static enum rym_code _rym_bg(
+        struct rym_ctx *ctx,
+        rt_uint8_t *buf,
+        rt_size_t len)
+{
+    struct custom_ctx *cctx = (struct custom_ctx*)ctx;
+    cctx->fpath[0] = '/';
+    /* the buf should be the file name */
+    strcpy(&(cctx->fpath[1]), buf);
+    cctx->fd = open(cctx->fpath, O_CREAT | O_WRONLY | O_TRUNC, 0);
+    if (cctx->fd < 0)
+    {
+        rt_err_t err = rt_get_errno();
+        rt_kprintf("error creating file: %d\n", err);
+        rt_kprintf("abort transmission\n");
+        return RYM_CODE_CAN;
+    }
+
+    cctx->flen = atoi(buf+strlen(buf)+1);
+    if (cctx->flen == 0)
+        cctx->flen = -1;
+    return RYM_CODE_ACK;
+}
+
+static enum rym_code _rym_tof(
+        struct rym_ctx *ctx,
+        rt_uint8_t *buf,
+        rt_size_t len)
+{
+    struct custom_ctx *cctx = (struct custom_ctx*)ctx;
+    RT_ASSERT(cctx->fd >= 0);
+    if (cctx->flen == -1)
+    {
+        write(cctx->fd, buf, len);
+    }
+    else
+    {
+        int wlen = len > cctx->flen ? cctx->flen : len;
+        write(cctx->fd, buf, wlen);
+        cctx->flen -= wlen;
+    }
+    return RYM_CODE_ACK;
+}
+
+static enum rym_code _rym_end(
+        struct rym_ctx *ctx,
+        rt_uint8_t *buf,
+        rt_size_t len)
+{
+    struct custom_ctx *cctx = (struct custom_ctx*)ctx;
+
+    RT_ASSERT(cctx->fd >= 0);
+    close(cctx->fd);
+    cctx->fd = -1;
+
+    return RYM_CODE_ACK;
+}
+
+rt_err_t rym_write_to_file(rt_device_t idev)
+{
+    rt_err_t res;
+    struct custom_ctx *ctx = rt_malloc(sizeof(*ctx));
+
+    RT_ASSERT(idev);
+
+    rt_kprintf("entering RYM mode\n");
+
+    res = rym_recv_on_device(&ctx->parent, idev,
+            _rym_bg, _rym_tof, _rym_end, 1000);
+
+    /* there is no Ymodem traffic on the line so print out info. */
+    rt_kprintf("leaving RYM mode with code %d\n", res);
+    rt_kprintf("file %s has been created.\n", ctx->fpath);
+
+    rt_free(ctx);
+
+    return res;
+}
+
+#ifdef RT_USING_FINSH
+#include <finsh.h>
+rt_err_t ry(char *dname)
+{
+    rt_err_t res;
+
+    rt_device_t dev = rt_device_find(dname);
+    if (!dev)
+    {
+        rt_kprintf("could not find device:%s\n", dname);
+        return -RT_ERROR;
+    }
+
+    res = rym_write_to_file(dev);
+
+    return res;
+}
+FINSH_FUNCTION_EXPORT(ry, receive files by ymodem protocol);
+#endif