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stlink: Use callback to increase frequency of trace data sampling

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The ST-LINK/V2 has limited internal buffering, such that trace data
can be missed if the target is generating data at a rate quicker than
the OpenOCD trace sampling. The issue of lost data is compounded since
individual TPIU packets may be split across individual STLINK_TRACE_EP
reads, and misleading results can occur if mid-packet loss occurs.

This patch increases the frequency of checking for pending trace data
with the aim of minimising such losses. Note: With the limited (I/O
and memory) bandwidth of the ST-LINK/V2 there cannot, however, be a
guarantee against trace data loss.

The timer callback is only added when enabling tracing, and is removed
when tracing is disabled.

Change-Id: Ibde9794b77793d3068f88cb5c1a26f9ceadcbd8a
Signed-off-by: James G. Smith <jsmith@ecoscentric.com>
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1661
Tested-by: jenkins
This commit is contained in:
Andreas Fritiofson
2014-03-07 20:08:31 +01:00
parent d82490adfb
commit 17fddb4289
3 changed files with 20 additions and 4 deletions
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20
src/jtag/drivers/stlink_usb.c
View File

@@ -830,6 +830,12 @@ static void stlink_usb_trace_read(void *handle)
}
}
static int stlink_usb_trace_read_callback(void *handle)
{
stlink_usb_trace_read(handle);
return ERROR_OK;
}
static enum target_state stlink_usb_v2_get_status(void *handle)
{
int result;
@@ -1006,8 +1012,10 @@ static void stlink_usb_trace_disable(void *handle)
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_APIV2_STOP_TRACE_RX;
res = stlink_usb_xfer(handle, h->databuf, 2);
if (res == ERROR_OK)
if (res == ERROR_OK) {
h->trace.enabled = false;
target_unregister_timer_callback(stlink_usb_trace_read_callback, handle);
}
}
@@ -1044,6 +1052,14 @@ static int stlink_usb_trace_enable(void *handle)
if (res == ERROR_OK) {
h->trace.enabled = true;
LOG_DEBUG("Tracing: recording at %" PRIu32 "Hz\n", trace_hz);
/* We need the trace read function to be called at a
* high-enough frequency to ensure reasonable
* "timeliness" in processing ITM/DWT data.
* TODO: An alternative could be using the asynchronous
* features of the libusb-1.0 API to queue up one or more
* reads in advance and requeue them once they are
* completed. */
target_register_timer_callback(stlink_usb_trace_read_callback, 1, 1, handle);
}
} else {
LOG_ERROR("Tracing is not supported by this version.");
@@ -1065,7 +1081,7 @@ static int stlink_usb_run(void *handle)
res = stlink_usb_write_debug_reg(handle, DCB_DHCSR, DBGKEY|C_DEBUGEN);
/* Try to start tracing, if requested */
if (res == ERROR_OK && h->trace.source_hz) {
if (res == ERROR_OK && h->trace.source_hz && !h->trace.enabled) {
if (stlink_usb_trace_enable(handle) == ERROR_OK)
LOG_DEBUG("Tracing: enabled\n");
else