m1n1/src/uartproxy.c

#include "proxy.h"
#include "string.h"
#include "types.h"
#include "uart.h"

typedef struct {
    u32 _pad;
    u32 type;
    union {
        ProxyRequest prequest;
        struct {
            u64 addr;
            u64 size;
            u32 dchecksum;
        } mrequest;
    };
    u32 checksum;
} UartRequest;

typedef struct {
    u32 type;
    u32 status;
    union {
        ProxyReply preply;
        struct {
            u32 dchecksum;
        } mreply;
    };
    u32 checksum;
} UartReply;

#define REQ_NOP 0x00AA55FF
#define REQ_PROXY 0x01AA55FF
#define REQ_MEMREAD 0x02AA55FF
#define REQ_MEMWRITE 0x03AA55FF

#define ST_OK 0
#define ST_BADCMD -1
#define ST_INVAL -2
#define ST_XFRERR -3
#define ST_CRCERR -4

// I just totally pulled this out of my arse
u32 checksum(void *start, u32 length)
{
    u32 sum = 0xDEADBEEF;
    u8 *d = (u8 *)start;

    while (length--) {
        sum *= 31337;
        sum += (*d++) ^ 0x5A;
    }
    return sum ^ 0xADDEDBAD;
}

void uartproxy_run(void)
{
    int running = 1;
    int c;
    u32 bytes;

    UartRequest request;
    UartReply reply;

    while (running) {
        c = uart_getbyte();
        if (c != 0xFF)
            continue;
        c = uart_getbyte();
        if (c != 0x55)
            continue;
        c = uart_getbyte();
        if (c != 0xAA)
            continue;
        c = uart_getbyte();
        if (c < 0)
            continue;
        memset(&request, 0, sizeof(request));
        request.type = 0x00AA55FF | ((c & 0xff) << 24);
        bytes = uart_read((&request.type) + 1, sizeof(request) - 4);
        if (bytes != (sizeof(UartRequest) - 4))
            continue;
        if (checksum(&(request.type), sizeof(request) - 8) != request.checksum)
            continue;

        memset(&reply, 0, sizeof(reply));
        reply.type = request.type;
        reply.status = ST_OK;

        switch (request.type) {
            case REQ_NOP:
                break;
            case REQ_PROXY:
                running = proxy_process(&request.prequest, &reply.preply);
                break;
            case REQ_MEMREAD:
                reply.mreply.dchecksum = checksum((void *)request.mrequest.addr,
                                                  request.mrequest.size);
                break;
            case REQ_MEMWRITE:
                bytes = uart_read((void *)request.mrequest.addr,
                                             request.mrequest.size);
                if (bytes != request.mrequest.size) {
                    reply.status = ST_XFRERR;
                    break;
                }
                reply.mreply.dchecksum = checksum((void *)request.mrequest.addr,
                                                  request.mrequest.size);
                if (reply.mreply.dchecksum != request.mrequest.dchecksum)
                    reply.status = ST_XFRERR;
                break;
            default:
                reply.status = ST_BADCMD;
                break;
        }
        reply.checksum = checksum(&reply, sizeof(reply) - 4);
        uart_write(&reply, sizeof(reply));

        if ((request.type == REQ_MEMREAD) && (reply.status == ST_OK)) {
            uart_write((void *)request.mrequest.addr,
                                 request.mrequest.size);
        }
    }
}