drivers/kitprog: workaround KitProg firmware bug of missing ZLP

[fw/openocd] / src / jtag / drivers / kitprog.c

diff --git a/src/jtag/drivers/kitprog.c b/src/jtag/drivers/kitprog.c
index db5b62e2e56efe8f9eb52009b8aa0067dcf75e59..522eb17bb735e35fbd6c925ce7cf5b9eff3b2363 100644 (file)
--- a/src/jtag/drivers/kitprog.c
+++ b/src/jtag/drivers/kitprog.c
@@ -741,12 +741,22 @@ static int kitprog_swd_run_queue(void)
                        break;
                }
 
-               /* We use the maximum buffer size here because the KitProg sometimes
-                * doesn't like bulk reads of fewer than 62 bytes. (?!?!)
+               /* KitProg firmware does not send a zero length packet
+                * after the bulk-in transmission of a length divisible by bulk packet
+                * size (64 bytes) as required by the USB specification.
+                * Therefore libusb would wait for continuation of transmission.
+                * Workaround: Limit bulk read size to expected number of bytes
+                * for problematic tranfer sizes. Otherwise use the maximum buffer
+                * size here because the KitProg sometimes doesn't like bulk reads
+                * of fewer than 62 bytes. (?!?!)
                 */
+               size_t read_count_workaround = SWD_MAX_BUFFER_LENGTH;
+               if (read_count % 64 == 0)
+                       read_count_workaround = read_count;
+
                ret = jtag_libusb_bulk_read(kitprog_handle->usb_handle,
                                BULK_EP_IN | LIBUSB_ENDPOINT_IN, (char *)buffer,
-                               SWD_MAX_BUFFER_LENGTH, 0);
+                               read_count_workaround, 1000);
                if (ret > 0) {
                        /* Handle garbage data by offsetting the initial read index */
                        if ((unsigned int)ret > read_count)