Skip to content

Consume POLL body to ETX before replying to avoid RS-485 bus contention #30

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
brocci wants to merge 1 commit into
base: master
Choose a base branch
from
Open

Consume POLL body to ETX before replying to avoid RS-485 bus contention #30

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 7 additions & 1 deletion src/CMRI.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -202,7 +202,9 @@ uint8_t CMRI::_decode(uint8_t c)
else if (c == INIT)
_mode = DECODE_DATA;
else if (c == POLL)
goto POSTAMBLE_POLL;
// Consume poll body via IGNORE_DATA until ETX (DLE-aware),
// then reply from POSTAMBLE_IGNORE.
_mode = IGNORE_DATA;
else
_mode = POSTAMBLE_OTHER;
break;
Expand Down Expand Up @@ -261,5 +263,9 @@ uint8_t CMRI::_decode(uint8_t c)

POSTAMBLE_IGNORE:
_mode = PREAMBLE_1;
// POLL frames consume body to ETX above; reply after ETX
// to avoid RS-485 bus contention (host still transmitting).
if (_rx_packet_type == POLL)
return POLL;
return NOOP;
}
50 changes: 50 additions & 0 deletions test/test_cmri/test_main.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,53 @@ void test_transmit_escapes_control_bytes(void)
TEST_ASSERT_EQUAL_UINT8(CMRI::ETX, s.tx[10]);
}

// A well-formed POLL waits for ETX before replying.
void test_poll_waits_for_etx(void)
{
Stream s;
CMRI cmri(0, 24, 48, s);

cmri.set_byte(0, 0x55);

feed_packet(s, 0, CMRI::POLL, nullptr, 0);
TEST_ASSERT_TRUE(cmri.process());
TEST_ASSERT_EQUAL_UINT8(CMRI::GET, s.tx[4]);
TEST_ASSERT_EQUAL_UINT8(0x55, s.tx[5]);
}

// A POLL without ETX produces no reply.
void test_poll_truncated_no_reply(void)
{
Stream s;
CMRI cmri(0, 24, 48, s);

cmri.set_byte(0, 0x55);

s.feed(0xFF);
s.feed(0xFF);
s.feed(CMRI::STX);
s.feed('A' + 0);
s.feed(CMRI::POLL);

TEST_ASSERT_FALSE(cmri.process());
TEST_ASSERT_EQUAL_UINT(0u, s.tx.size());
}

// A POLL with body bytes waits for ETX before replying.
void test_poll_with_body_waits_for_etx(void)
{
Stream s;
CMRI cmri(0, 24, 48, s);

cmri.set_byte(0, 0x77);

uint8_t body[2] = {0x01, 0x02};
feed_packet(s, 0, CMRI::POLL, body, 2);
TEST_ASSERT_TRUE(cmri.process());
TEST_ASSERT_EQUAL_UINT8(CMRI::GET, s.tx[4]);
TEST_ASSERT_EQUAL_UINT8(0x77, s.tx[5]);
}

// Garbage before a valid packet is resynced away by the preamble state machine.
void test_preamble_resync_after_garbage(void)
{
Expand Down Expand Up @@ -205,6 +252,9 @@ int main(int, char **)
RUN_TEST(test_set_packet_updates_outputs);
RUN_TEST(test_address_filtering);
RUN_TEST(test_transmit_escapes_control_bytes);
RUN_TEST(test_poll_waits_for_etx);
RUN_TEST(test_poll_truncated_no_reply);
RUN_TEST(test_poll_with_body_waits_for_etx);
RUN_TEST(test_preamble_resync_after_garbage);
return UNITY_END();
}