pocketbus.c

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#include "pocketbus.h"

#include <cfg/macros.h>
#include <cfg/debug.h>

#include <kern/kfile.h>

#include <cpu/byteorder.h>

#include <string.h>

void pocketbus_putchar(struct PocketBusCtx *ctx, uint8_t c)
{
    /* Update checksum */
    rotating_update1(c, &ctx->out_cks);

    /* Escape characters with special meaning */
    if (c == POCKETBUS_ESC || c == POCKETBUS_STX || c == POCKETBUS_ETX)
        kfile_putc(POCKETBUS_ESC, ctx->fd);
    
    kfile_putc(c, ctx->fd);
}

void pocketbus_begin(struct PocketBusCtx *ctx, pocketbus_addr_t addr)
{
    PocketBusHdr hdr;

    hdr.ver = POCKETBUS_VER;
    hdr.addr = cpu_to_be16(addr);
    rotating_init(&ctx->out_cks);

    /* Send STX */
    kfile_putc(POCKETBUS_STX, ctx->fd);
    
    /* Send header */
    pocketbus_write(ctx, &hdr, sizeof(hdr));
}

void pocketbus_write(struct PocketBusCtx *ctx, const void *_data, size_t len)
{
    const uint8_t *data = (const uint8_t *)_data;

    while (len--)
        pocketbus_putchar(ctx, *data++);
}

void pocketbus_end(struct PocketBusCtx *ctx)
{
    /* Send checksum */
    rotating_t cks = cpu_to_be16(ctx->out_cks);
    pocketbus_write(ctx, &cks, sizeof(cks));

    /* Send ETX */
    kfile_putc(POCKETBUS_ETX, ctx->fd);
}

void pocketbus_send(struct PocketBusCtx *ctx, pocketbus_addr_t addr, const void *data, size_t len)
{
    pocketbus_begin(ctx, addr);

    /* Send data */
    pocketbus_write(ctx, data, len);

    pocketbus_end(ctx);
}


bool pocketbus_recv(struct PocketBusCtx *ctx, struct PocketMsg *msg)
{
    int c;

    /* Process incoming characters until buffer is not empty */
    while ((c = kfile_getc(ctx->fd)) != EOF)
    {
        /* Look for STX char */
        if (c == POCKETBUS_STX && !ctx->escape)
        {
            /* When an STX is found, inconditionally start a new packet */
            if (ctx->sync)
                kprintf("pocketBus double sync!\n");

            ctx->sync = true;
            ctx->len = 0;
            rotating_init(&ctx->in_cks);
            continue;
        }

        if (ctx->sync)
        {
            /* Handle escape mode */
            if (c == POCKETBUS_ESC && !ctx->escape)
            {
                ctx->escape = true;
                continue;
            }

            /* Handle message end */
            if (c == POCKETBUS_ETX && !ctx->escape)
            {
                ctx->sync = false;

                /* Check minimum size */
                if (ctx->len < sizeof(PocketBusHdr) + sizeof(rotating_t))
                {
                    kprintf("pocketBus short pkt!\n");
                    continue;
                }

                /* Remove checksum bytes from packet len */
                ctx->len -= sizeof(rotating_t);

                /* Compute checksum */
                rotating_update(ctx->buf, ctx->len, &ctx->in_cks);
                rotating_t recv_cks = be16_to_cpu(*((rotating_t *)(ctx->buf + ctx->len)));

                /* Checksum check */
                if (recv_cks == ctx->in_cks)
                {
                    PocketBusHdr *hdr = (PocketBusHdr *)(ctx->buf);
                    /* Check packet version */
                    if (hdr->ver == POCKETBUS_VER)
                    {
                        /* Packet received, set msg fields */
                        msg->payload = ctx->buf + sizeof(PocketBusHdr);
                        msg->addr = be16_to_cpu(hdr->addr);
                        msg->len = ctx->len - sizeof(PocketBusHdr);
                        msg->ctx = ctx;
                        return true;
                    }
                    else
                    {
                        kprintf("pocketBus version mismatch, here[%d], there[%d]\n", POCKETBUS_VER, hdr->ver);
                        continue;
                    }
                }
                else
                {
                    kprintf("pocketBus cks error, here[%04X], there[%04X]\n", ctx->in_cks, recv_cks);
                    continue;
                }

            }

            ctx->escape = false;

            /* Check buffer overflow: simply ignore
               received data and go to unsynced state. */
            if (ctx->len >= CONFIG_POCKETBUS_BUFLEN)
            {
                kprintf("pocketBus buffer overflow\n");
                ctx->sync = false;
                continue;
            }

            /* Put received data in the buffer */
            ctx->buf[ctx->len] = c;
            ctx->len++;
        }
    }

    /*
     * Check stream status.
     */
    if (kfile_error(ctx->fd))
    {
        TRACEMSG("fd status[%04X]", kfile_error(ctx->fd));
        kfile_clearerr(ctx->fd);
    }

    return false;
}


void pocketbus_init(struct PocketBusCtx *ctx, struct KFile *fd)
{
    ASSERT(ctx);
    ASSERT(fd);

    memset(ctx, 0, sizeof(*ctx));
    ctx->fd = fd;
}