Mitig: do TMR check before sending PEC checksum

common/src/i2c_slave.c

@@ -30,6 +30,7 @@ static cmd_space_t *ext_cmds;
 
 uint16_t use_pec __xMR = 0;
 static uint16_t pec_checksum __xMR;
+static uint8_t tmp_pec_checksum;
 static uint8_t checksum_from_m;
 static uint16_t added_tx_pec __xMR = 0;
 static uint16_t sent_checksum __xMR = 0;
@@ -229,7 +230,8 @@ static void __xMR I2C_tx_pending(const struct i2c_s_async_descriptor *const desc
                         set_cmd(descr, 3);
                         ++cmd_len;
                 } else if (use_pec && !sent_checksum) {
-                        io_write(io, (uint8_t *)&pec_checksum, 1);
+                        tmp_pec_checksum = pec_checksum;
+                        io_write(io, (uint8_t *)&tmp_pec_checksum, 1);
                         set_cmd(descr, 3);
                         sent_checksum = 1;
                 } else {
@@ -254,7 +256,8 @@ static void __xMR I2C_tx_pending(const struct i2c_s_async_descriptor *const desc
                         set_cmd(descr, 3);
                         ++cmd_len;
                 } else if (use_pec && !sent_checksum) {
-                        io_write(io, (uint8_t *)&pec_checksum, 1);
+                        tmp_pec_checksum = pec_checksum;
+                        io_write(io, (uint8_t *)&tmp_pec_checksum, 1);
                         set_cmd(descr, 3);
                         sent_checksum = 1;
                 } else {