Hello Thomas,
>>>>> "Thomas" == Thomas Jarosch <thomas.jarosch@xxxxxxxxxxxxx> writes:
...
Thomas> May I ask for a small follow up patch as this is an example code
Thomas> others could learn from?
Thomas> - Replace magic numbers "15" and "3" in the code with constants.
Thomas> - Have a short description what the code does at the beginning
Thomas> of the file. Ideally describe that it's using MPSEE mode or
Thomas> actually why it's using that.
Thomas> In fact it currently states:
Thomas> "LIBFTDI EEPROM access example"
Thomas> :D
Thomas> - Regarding the "while (index < 3)" loop: Here's a part that I'm
Thomas> a bit unsure about: Should we add a safety exit condition to the
Thomas> loop?
Thomas> [Just a few days ago I debugged a full spool partiton on a
Thomas> customer machine because the fax subsystem was stuck in an
Thomas> endless loop outputting five log messages per second. The code
Thomas> in question included a newly added rate limiting code and other
Thomas> safety measures, but somehow the exit condition of the loop
Thomas> still wasn't triggered]
Thomas> NASA "code rule" number two comes to mind:
Thomas>
https://en.wikipedia.org/wiki/The_Power_of_10:_Rules_for_Developing_Safety-Critical_Code
Thomas> "2. All loops must have fixed bounds. This prevents runaway
Thomas> code."
Are checks and a resulting break allowed inside an infinit loop?
Please find a code cleanup appended.
Bye
--
Uwe Bonnes bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------
>From 687cd1de886b40a70c3d1998463505e9c6db8916 Mon Sep 17 00:00:00 2001
From: Uwe Bonnes <bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 1 Jun 2018 11:18:01 +0200
Subject: examples/async.c: Cleanup and explanations.
---
examples/async.c | 56 ++++++++++++++++++++++++++++++++++++++++++++------------
1 file changed, 44 insertions(+), 12 deletions(-)
diff --git a/examples/async.c b/examples/async.c
index 08457b9..0589479 100644
--- a/examples/async.c
+++ b/examples/async.c
@@ -1,8 +1,22 @@
-/* LIBFTDI EEPROM access example
+/* Libftdi example for asynchronous read/write.
This program is distributed under the GPL, version 2
*/
+/* This programm switches to MPSSE mode, and sets and then reads back
+ * the high byte 3 times with three different values.
+ * The expected read values are hard coded in ftdi_init
+ * with 0x00, 0x55 and 0xaa
+ *
+ * Make sure that that nothing else drives some bit of the high byte
+ * or expect a collision for a very short time and some differences
+ * in the data read back.
+ *
+ * Result should be the same without any option or with either
+ * -r or -w or -b.
+ */
+
+
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -49,7 +63,7 @@ int main(int argc, char **argv)
}
}
- // Select first interface
+ /* Select first free interface */
ftdi_set_interface(ftdi, INTERFACE_ANY);
struct ftdi_device_list *devlist;
@@ -101,41 +115,59 @@ int main(int argc, char **argv)
err, ftdi_get_error_string(ftdi));
return -1;
}
- uint8_t ftdi_init[15] = {TCK_DIVISOR, 0x00, 0x00,
+#define DATA_TO_READ 3
+ uint8_t ftdi_init[] = {TCK_DIVISOR, 0x00, 0x00,
+ /* Set High byte to zero.*/
SET_BITS_HIGH, 0, 0xff,
GET_BITS_HIGH,
+ /* Set High byte to 0x55.*/
SET_BITS_HIGH, 0x55, 0xff,
GET_BITS_HIGH,
+ /* Set High byte to 0xaa.*/
SET_BITS_HIGH, 0xaa, 0xff,
- GET_BITS_HIGH};
+ GET_BITS_HIGH,
+ /* Set back to high impedance.*/
+ SET_BITS_HIGH, 0x00, 0x00 };
struct ftdi_transfer_control *tc_read;
struct ftdi_transfer_control *tc_write;
uint8_t data[3];
if (do_read) {
- tc_read = ftdi_read_data_submit(ftdi, data, 3);
+ tc_read = ftdi_read_data_submit(ftdi, data, DATA_TO_READ);
}
if (do_write) {
- tc_write = ftdi_write_data_submit(ftdi, ftdi_init, 15);
+ tc_write = ftdi_write_data_submit(ftdi, ftdi_init, sizeof(ftdi_init));
int transfer = ftdi_transfer_data_done(tc_write);
- printf("Async write %d\n", transfer);
+ if (transfer != sizeof(ftdi_init)) {
+ printf("Async write failed : %d\n", transfer);
+ }
} else {
- int written = ftdi_write_data(ftdi, ftdi_init, 15);
- if (written != 15) {
- printf("Sync write failed\n");
+ int written = ftdi_write_data(ftdi, ftdi_init, sizeof(ftdi_init));
+ if (written != sizeof(ftdi_init)) {
+ printf("Sync write failed: %d\n", written);
}
}
if (do_read) {
int transfer = ftdi_transfer_data_done(tc_read);
- printf("Async Read %d\n", transfer);
+ if (transfer != DATA_TO_READ) {
+ printf("Async Read failed:%d\n", transfer);
+ }
} else {
int index = 0;
- while (index < 3) {
+ ftdi->usb_read_timeout = 1;
+ int i = 1000; /* Fail if read did not succeed in 1 second.*/
+ while (i--) {
int res = ftdi_read_data(ftdi, data + index, 3 - index);
if (res < 0) {
printf("Async read failure at %d\n", index);
} else {
index += res;
}
+ if (res == 3) {
+ break;
+ }
+ }
+ if (i < 1) {
+ printf("Async read unsuccessfull\n");
}
}
printf("Read %02x %02x %02x\n", data[0], data[1], data[2]);
--
2.13.6
--
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