uni-t-ut32x: rephrase the receive buffer and packets relation

[libsigrok.git] / src / hardware / uni-t-ut32x / protocol.c

diff --git a/src/hardware/uni-t-ut32x/protocol.c b/src/hardware/uni-t-ut32x/protocol.c
index 7d69091eab77eba1cc2ce839b91952aa0b7f744b..4da246626012cc45b5dd620ef6818a2e9246c4be 100644 (file)
--- a/src/hardware/uni-t-ut32x/protocol.c
+++ b/src/hardware/uni-t-ut32x/protocol.c
@@ -156,6 +156,62 @@ static void process_packet(struct sr_dev_inst *sdi, uint8_t *pkt, size_t len)
                sr_dev_acquisition_stop(sdi);
 }
 
+static int process_buffer(struct sr_dev_inst *sdi)
+{
+       struct dev_context *devc;
+       uint8_t *pkt;
+       size_t remain, idx;
+
+       /*
+        * Specifically do not insist on finding the packet boundary at
+        * the end of the most recently received data chunk. Serial
+        * ports might involve hardware buffers (FIFO). We want to sync
+        * as fast as possible.
+        *
+        * Handle the synchronized situation first. Process complete
+        * packets that reside at the start of the buffer. Then fallback
+        * to incomplete or unaligned packets if the receive buffer
+        * still contains data bytes. (Depending on the bitrate and the
+        * poll interval, we may always end up in the manual search. But
+        * considering the update rate - two or three packets per second
+        * - this is not an issue.)
+        */
+       devc = sdi->priv;
+       pkt = &devc->packet[0];
+       while (devc->packet_len >= PACKET_SIZE &&
+                       pkt[PACKET_SIZE - 2] == SEP[0] &&
+                       pkt[PACKET_SIZE - 1] == SEP[1]) {
+               process_packet(sdi, &pkt[0], PACKET_SIZE);
+               remain = devc->packet_len - PACKET_SIZE;
+               if (remain)
+                       memmove(&pkt[0], &pkt[PACKET_SIZE], remain);
+               devc->packet_len -= PACKET_SIZE;
+       }
+
+       /*
+        * The 'for' loop and the increment upon re-iteration after
+        * setting the loop var to zero is not an issue. The marker has
+        * two bytes, so effectively starting the search at offset 1 is
+        * fine for the specific packet layout.
+        */
+       for (idx = 0; idx < devc->packet_len; idx++) {
+               if (idx < 1)
+                       continue;
+               if (pkt[idx - 1] != SEP[0] || pkt[idx] != SEP[1])
+                       continue;
+               /* Found a packet that spans up to and including 'idx'. */
+               idx++;
+               process_packet(sdi, &pkt[0], idx);
+               remain = devc->packet_len - idx;
+               if (remain)
+                       memmove(&pkt[0], &pkt[idx], remain);
+               devc->packet_len -= idx;
+               idx = 0;
+       }
+
+       return 0;
+}
+
 SR_PRIV void LIBUSB_CALL uni_t_ut32x_receive_transfer(struct libusb_transfer *transfer)
 {
        struct dev_context *devc;
@@ -171,19 +227,16 @@ SR_PRIV void LIBUSB_CALL uni_t_ut32x_receive_transfer(struct libusb_transfer *tr
                memcpy(devc->packet + devc->packet_len, transfer->buffer + 1,
                                hid_payload_len);
                devc->packet_len += hid_payload_len;
-               if (devc->packet_len >= 2
-                               && devc->packet[devc->packet_len - 2] == SEP[0]
-                               && devc->packet[devc->packet_len - 1] == SEP[1]) {
-                       /* Got end of packet. */
-                       process_packet(sdi, devc->packet, devc->packet_len);
-                       devc->packet_len = 0;
-               } else if (devc->packet_len > PACKET_SIZE) {
-                       /* Guard against garbage from the device overrunning
-                        * our packet buffer. */
-                       sr_dbg("Buffer overrun!");
-                       process_packet(sdi, devc->packet, devc->packet_len);
+               /*
+                * Discard receive data when the buffer is exhausted. This shall
+                * allow to (re-)synchronize to the data stream when we find it
+                * in an arbitrary state. Check the receive buffer for packets.
+                */
+               if (devc->packet_len == sizeof(devc->packet)) {
+                       process_packet(sdi, &devc->packet[0], devc->packet_len);
                        devc->packet_len = 0;
                }
+               process_buffer(sdi);
        }
 
        /* Get the next transfer (unless we're shutting down). */