From: Stefan Brüns <redacted>
Date: Sun, 17 Apr 2016 17:14:27 +0000 (+0200)
Subject: hameg-hmo: Also start reading on timeout (workaround for USBTMC)
X-Git-Tag: libsigrok-0.5.0~505
X-Git-Url: https://sigrok.org/gitaction?a=commitdiff_plain;h=f4f273ce1e718342b8de34b98786131102d7bcaa;p=libsigrok.git

hameg-hmo: Also start reading on timeout (workaround for USBTMC)

scpi_serial generate an POLLIN event after the requested data is returned
by the instrument. For USBTMC it is necessary to
1. send an REQUEST_DEV_DEP_MSG_IN request
2. submit an USB bulk read transfer asynchronously.

Using the synchronous libusb_bulk_read() does not generate an POLLIN event.

Solving this properly needs major surgery in spci_usbtmc_libusb.
---

diff --git a/src/hardware/hameg-hmo/protocol.c b/src/hardware/hameg-hmo/protocol.c
index 9d32dc67..bd2174a7 100644
--- a/src/hardware/hameg-hmo/protocol.c
+++ b/src/hardware/hameg-hmo/protocol.c
@@ -743,8 +743,12 @@ SR_PRIV int hmo_receive_data(int fd, int revents, void *cb_data)
 	if (!(devc = sdi->priv))
 		return TRUE;
 
+	/* Although this is correct in general, the USBTMC libusb implementation
+	 * currently does not generate an event prior to the first read. Often
+	 * it is ok to start reading just after the 50ms timeout. See bug #785.
 	if (revents != G_IO_IN)
 		return TRUE;
+	*/
 
 	ch = devc->current_channel->data;