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Fix missing STX (0x02) DLE-escape in transmit() #19

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Fix missing STX (0x02) DLE-escape in transmit() #19

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7 changes: 3 additions & 4 deletions src/CMRI.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -143,10 +143,9 @@ void CMRI::transmit()
_serial.write(GET);
for (int i = 0; i < _tx_length; i++)
{
if (_tx_buffer[i] == ETX)
_serial.write(ESC); // escape because this looks like an STX bit (very basic protocol)
if (_tx_buffer[i] == ESC)
_serial.write(ESC); // escape because this looks like an escape bit (very basic protocol)
// DLE-escape STX, ETX and DLE characters
if (_tx_buffer[i] == STX || _tx_buffer[i] == ETX || _tx_buffer[i] == ESC)
_serial.write(ESC);
_serial.write(_tx_buffer[i]);
}
_serial.write(ETX);
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10 changes: 6 additions & 4 deletions test/test_cmri/test_main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -61,9 +61,11 @@ void test_set_bit_reflected_in_transmit(void)
cmri.transmit();

// Frame: FF FF STX 'A' GET <3 data bytes> ETX
TEST_ASSERT_EQUAL_UINT8(0x01, s.tx[5]); // byte 0, bit 0
TEST_ASSERT_EQUAL_UINT8(0x02, s.tx[6]); // byte 1, bit 1
TEST_ASSERT_EQUAL_UINT8(0x00, s.tx[7]);
// byte 1 = 0x02 (STX), so it gets DLE-escaped to ESC 0x02
TEST_ASSERT_EQUAL_UINT8(0x01, s.tx[5]); // byte 0, bit 0
TEST_ASSERT_EQUAL_UINT8(CMRI::ESC, s.tx[6]); // DLE escape for byte 1 (STX value)
TEST_ASSERT_EQUAL_UINT8(0x02, s.tx[7]); // byte 1, bit 1
TEST_ASSERT_EQUAL_UINT8(0x00, s.tx[8]); // byte 2
}

// Regression for the set_bit() bounds bug: the old (pos + 7) / 8 check wrongly
Expand Down Expand Up @@ -154,7 +156,7 @@ void test_address_filtering(void)
TEST_ASSERT_EQUAL_UINT8(0, cmri.get_byte(0));
}

// Data bytes that collide with ETX/ESC are escaped in the transmitted frame.
// Data bytes that collide with STX, ETX or ESC are escaped in the transmitted frame.
void test_transmit_escapes_control_bytes(void)
{
Stream s;
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