m1n1/src/uartproxy.c

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/* SPDX-License-Identifier: MIT */
#include "uartproxy.h"
#include "exception.h"
#include "iodev.h"
#include "proxy.h"
#include "string.h"
#include "types.h"
#include "utils.h"
#define REQ_SIZE 64
typedef struct {
u32 _pad;
u32 type;
union {
ProxyRequest prequest;
struct {
u64 addr;
u64 size;
u32 dchecksum;
} mrequest;
};
u32 checksum;
} UartRequest;
#define REPLY_SIZE 36
typedef struct {
u32 type;
s32 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 REQ_BOOT 0x04AA55FF
#define ST_OK 0
#define ST_BADCMD -1
#define ST_INVAL -2
#define ST_XFRERR -3
#define ST_CSUMERR -4
static u32 iodev_proxy_buffer[IODEV_MAX];
// I just totally pulled this out of my arse
// Noinline so that this can be bailed out by exc_guard = EXC_RETURN
// We assume this function does not use the stack
static u64 __attribute__((noinline)) 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;
size_t bytes;
u64 checksum_val;
iodev_id_t iodev = IODEV_MAX;
UartRequest request;
UartReply reply = {REQ_BOOT};
reply.checksum = checksum(&reply, REPLY_SIZE - 4);
// Startup notification only goes out via UART
iodev_write(IODEV_UART, &reply, REPLY_SIZE);
while (running) {
for (iodev = 0; iodev < IODEV_MAX;) {
u8 b;
iodev_handle_events(iodev);
if (iodev_can_read(iodev) && iodev_read(iodev, &b, 1) == 1) {
iodev_proxy_buffer[iodev] >>= 8;
iodev_proxy_buffer[iodev] |= b << 24;
if ((iodev_proxy_buffer[iodev] & 0xffffff) == 0xAA55FF)
break;
}
iodev++;
if (iodev == IODEV_MAX)
iodev = 0;
}
memset(&request, 0, sizeof(request));
request.type = iodev_proxy_buffer[iodev];
bytes = iodev_read(iodev, (&request.type) + 1, REQ_SIZE - 4);
if (bytes != REQ_SIZE - 4)
continue;
if (checksum(&(request.type), REQ_SIZE - 4) != request.checksum) {
memset(&reply, 0, sizeof(reply));
reply.type = request.type;
reply.status = ST_CSUMERR;
reply.checksum = checksum(&reply, REPLY_SIZE - 4);
iodev_write(iodev, &reply, REPLY_SIZE);
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:
if (request.mrequest.size == 0)
break;
exc_count = 0;
exc_guard = GUARD_RETURN;
checksum_val = checksum((void *)request.mrequest.addr, request.mrequest.size);
exc_guard = GUARD_OFF;
if (exc_count)
reply.status = ST_XFRERR;
reply.mreply.dchecksum = checksum_val;
break;
case REQ_MEMWRITE:
exc_count = 0;
exc_guard = GUARD_SKIP;
if (request.mrequest.size != 0) {
// Probe for exception guard
// We can't do the whole buffer easily, because we'd drop UART data
write8(request.mrequest.addr, 0);
write8(request.mrequest.addr + request.mrequest.size - 1, 0);
}
exc_guard = GUARD_OFF;
if (exc_count) {
reply.status = ST_XFRERR;
break;
}
bytes = iodev_read(iodev, (void *)request.mrequest.addr, request.mrequest.size);
if (bytes != request.mrequest.size) {
reply.status = ST_XFRERR;
break;
}
checksum_val = checksum((void *)request.mrequest.addr, request.mrequest.size);
reply.mreply.dchecksum = checksum_val;
if (reply.mreply.dchecksum != request.mrequest.dchecksum)
reply.status = ST_XFRERR;
break;
default:
reply.status = ST_BADCMD;
break;
}
reply.checksum = checksum(&reply, REPLY_SIZE - 4);
iodev_write(iodev, &reply, REPLY_SIZE);
if ((request.type == REQ_MEMREAD) && (reply.status == ST_OK)) {
iodev_write(iodev, (void *)request.mrequest.addr, request.mrequest.size);
}
}
}