jtag: drivers: buspirate: chunk SWD switch sequence transfer.

Commit c2e18bf changed the size of the JTAG-to-SWD sequence
from 15 bytes to 17 bytes. This broke SWD switch sequence transfer
for buspirate, since buspirate packets can only hold a payload of up
to 16 bytes and we tried to fit the whole sequence in a single packet.

Splitting up the sequence transfer in appropriately sized packets
makes buspirate SWD work again (successfully tested with buspirate
firmwares v6.1 and v7.0).

Change-Id: Ib5b412b9e77287d705d2762e31c16d30318b50e3
Signed-off-by: Tilman Sauerbeck <[email protected]>
Reviewed-on: http:https://openocd.zylin.com/5200
Tested-by: jenkins
Reviewed-by: Antonio Borneo <[email protected]>
Reviewed-by: Tomas Vanek <[email protected]>

src/jtag/drivers/buspirate.c

@@ -1312,7 +1312,7 @@ static int buspirate_swd_switch_seq(enum swd_special_seq seq)
 {
  const uint8_t *sequence;
  int sequence_len;
- uint8_t tmp[64];
+ uint32_t no_bytes, sequence_offset;
 
  switch (seq) {
  case LINE_RESET:
@@ -1335,15 +1335,24 @@ static int buspirate_swd_switch_seq(enum swd_special_seq seq)
  return ERROR_FAIL;
  }
 
- /* FIXME: all above sequences fit into one pirate command for now
- * but it may cause trouble later
- */
+ no_bytes = sequence_len;
+ sequence_offset = 0;
+
+ while (no_bytes) {
+ uint8_t tmp[17];
+ uint32_t to_send;
+
+ to_send = no_bytes > 16 ? 16 : no_bytes;
+
+ tmp[0] = 0x10 + ((to_send - 1) & 0x0F);
+ memcpy(tmp + 1, &sequence[sequence_offset], to_send);
 
- tmp[0] = 0x10 + ((sequence_len - 1) & 0x0F);
- memcpy(tmp + 1, sequence, sequence_len);
+  buspirate_serial_write(buspirate_fd, tmp, to_send + 1);
+  buspirate_serial_read(buspirate_fd, tmp, to_send + 1);
 
- buspirate_serial_write(buspirate_fd, tmp, sequence_len + 1);
- buspirate_serial_read(buspirate_fd, tmp, sequence_len + 1);
+ no_bytes -= to_send;
+ sequence_offset += to_send;
+ }
 
  return ERROR_OK;
 }