Hi,
I am a newbie to this process so please tell me if I need to make
changes to this message.
I wish to submit an enhancement to replace the original get_packet()
function in kgdb.c. Please give me some feedback.
My modification uses a state based packet detection routine and allows
for fast recovery from bit errors and missing characters in the received
packet. The old get_packet() can easily fail to recover quickly and
therefore will have poor performance when the comms are not 100% good.
Here is my patch for kgdb.c, I've attached my patch file as evolution
seems to corrupt my source code if I paste the code directly into my e-
mail. For example, evolution adds linewrap and seems to remove tabs.
Regards,
Dean.
26a27,31
> *
> * Modified by Dean Jenkins
> * Copyright (C) 2006 Liberte Software Ltd. <[EMAIL PROTECTED]>
> * get_packet() made more robust to avoid loss of the next "good" received
> packet.
> *
340a346,353
> typedef enum {
> WAIT_DOLLAR,
> GOT_DOLLAR,
> GOT_HASH,
> GOT_CHK1,
> GOOD_PACKET
> } rx_state;
>
344,346c357,359
< unsigned char checksum;
< unsigned char xmitcsum;
< int count;
---
> unsigned char checksum = 0;
> unsigned char xmitcsum = 0;
> int count = 0, hexvalue;
348,356c361
< if (!kgdb_io_ops.read_char)
< return;
< do {
< /* Spin and wait around for the start character, ignore all
< * other characters */
< while ((ch = (kgdb_io_ops.read_char())) != '$') ;
< kgdb_connected = 1;
< checksum = 0;
< xmitcsum = -1;
---
> rx_state state = WAIT_DOLLAR;
358c363
< count = 0;
---
> while( state != GOOD_PACKET ) {
360,367c365,376
< /* now, read until a # or end of buffer is found */
< while (count < (BUFMAX - 1)) {
< ch = kgdb_io_ops.read_char();
< if (ch == '#')
< break;
< checksum = checksum + ch;
< buffer[count] = ch;
< count = count + 1;
---
> /* read a character ( uses blocking ) */
> ch = kgdb_io_ops.read_char();
>
> if( ch == '$' ) {
> /* start of new packet */
> /* abandon any old packet processing */
> /* as incomplete packet received */
>
> checksum = 0;
> count = 0;
>
> state = GOT_DOLLAR;
369c378,379
< buffer[count] = 0;
---
> else {
> switch (state) {
371,382c381,471
< if (ch == '#') {
< xmitcsum = hex(kgdb_io_ops.read_char()) << 4;
< xmitcsum += hex(kgdb_io_ops.read_char());
<
< if (checksum != xmitcsum)
< /* failed checksum */
< kgdb_io_ops.write_char('-');
< else
< /* successful transfer */
< kgdb_io_ops.write_char('+');
< if (kgdb_io_ops.flush)
< kgdb_io_ops.flush();
---
> case WAIT_DOLLAR:
> /* continue to wait for the next $ */
> break;
>
> case GOT_DOLLAR:
> /* receive the command */
>
> /* terminator found ? */
> if (ch == '#') {
> buffer[count] = 0;
> state = GOT_HASH;
> }
> else if (count < (BUFMAX - 1)) {
> checksum = checksum + ch;
> buffer[count] = ch;
> count = count + 1;
> }
> else {
> /* command is TOO long so abort
> */
> kgdb_io_ops.write_char('-');
>
> if (kgdb_io_ops.flush) {
> kgdb_io_ops.flush();
> }
>
> state = WAIT_DOLLAR;
> }
> break;
>
> case GOT_HASH:
> /* look at first checksum char */
> hexvalue = hex(ch);
>
> if( hexvalue == -1 ) {
> /* invalid hex char received so
> abort */
> kgdb_io_ops.write_char('-');
>
> if (kgdb_io_ops.flush) {
> kgdb_io_ops.flush();
> }
>
> state = WAIT_DOLLAR;
> }
> else {
> xmitcsum = hexvalue << 4;
> state = GOT_CHK1;
> }
> break;
>
> case GOT_CHK1:
> /* look at second checksum char */
> hexvalue = hex(ch);
>
> if( hexvalue == -1 ) {
> /* invalid hex char received so
> abort */
> kgdb_io_ops.write_char('-');
>
> if (kgdb_io_ops.flush) {
> kgdb_io_ops.flush();
> }
>
> state = WAIT_DOLLAR;
> }
> else {
> xmitcsum += hexvalue ;
>
> /* end of packet so now
> validate the checksum */
> if (checksum != xmitcsum) {
> /* failed checksum */
>
> kgdb_io_ops.write_char('-');
> /* bad packet so look
> for new packet */
> state = WAIT_DOLLAR;
> }
> else {
> /* successful transfer
> */
>
> kgdb_io_ops.write_char('+');
> /* exit as got a good
> packet */
> state = GOOD_PACKET;
> }
>
> if (kgdb_io_ops.flush) {
> kgdb_io_ops.flush();
> }
> }
> break;
>
> default:
> /* should never get here */
> state = WAIT_DOLLAR;
> break;
> }
384c473,475
< } while (checksum != xmitcsum);
---
> }
>
> kgdb_connected = 1;
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