Some note of Cyclic File in ETSI 102.221

Cyclic EF:
簡單說就是有每筆資料都是按照一定格式一筆一筆地儲存(record)，當最後一筆資料寫滿後，下一筆資料就會覆蓋第一筆資料再一筆一筆儲存下去。
最新的一筆(newest)就是record 1，最早的一筆(oldest)就是record n。

1. 根據ETSI 102.221 11.1.6 UPDATE RECORD 的定義:
Four modes are defined of which only PREVIOUS is allowed for cyclic files.

PREVIOUS:
For a cyclic EF the record containing the oldest data is updated, the record pointer is set to this record and this record becomes record number 1.

2. 根據ETSI 102.221 11.1.8 INCREASE
This function adds the value given by the terminal to the value of the last increased/updated record of the current cyclicEF, and stores the result into the oldest record. The record pointer is set to this record and this record becomes record number 1.

簡單說就是要更改cyclic EF只能使用"precious" update record 或是increase這兩個方法。最後一個更改的資料就是record number 1。

這裡簡單說明一下Increase command:
假設檔案內default的值都是(0 0 0) 3 bytes/per record

increase一筆資料為(0 0 1)

The data of record 1 (0 0 0) + new data in "increase" command(0 0 1) -> store to record N.
Set the record N to record 1:

這樣就完成INCREASE command囉~