Authors:	Jan Pazdera
	Tomas Martinek

The Time Stamp Unit (TSU) is designed to provide precise 64bits-wide Time Stamps using COMBO-PTM card. COMBO-PTM has precise Xtal (2ppm) and input for PPS GPS signal. TSU design is split into 2 parts, one of them is placed on the COMBO-PTM card (TSU_PTM design), second one resides at the COMBO6+add on interface card (TSU_ADD and TSU_COV design).

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TSU architecture

TSU_PTM design
COMBO PTM card design is a part of the whole TSU. It is dedicated to create and provide precise time stamp (3 modes) for add on card part. It must be initialized and adjusted by user drivers.

TSU_COV component
The TSU_COV design performs TSU_ADD handling by software. It makes available for software to request all three TSU modes (INIT, SHORT, FAST) and to read the actual time stamp value.

TSU ADD component
TSU_ADD component resides on add_on card provides transmition of time stamps (TS) from PTM card for the add on card design. There are three modes the TS can be transmitted by: INIT, SHORT and FAST mode. See below for more information.

TSU design is composed of PTM design (situated on COMBO PTM card) providing 96bits-wide Time Stamp generation, TSU_COV design, (situated on add-on card) providing TSU software handling and TSU_ADD design, (situated on add-on card) providing Time Stamp transfer from Combo PTM card (64bits-wide Time Stamp is transfered only).

Time Stamp is generated by TSU_PTM design and transmited by cable to add on card. This transmittion is driven by TSU_ADD design. Software driver can handle TSU requests and read Time Stamps by TSU_COV design.

TSU_PTM part must be initialized and adjusted before driver can request Time Stamp generation. It can be done eighter by PCI bus or by Microcontroller (situated on COMBO PTM card).

Note: TSU_PTM generates 96bits-wide Time Stamps but only higher 64 bits are transmited to TSU_ADD (as a result TSU provides 64bits-wide Time Stamps).

TSU_PTM transmits Time Stamps in 3 modes: INIT, SHORT and FAST.

• INIT mode: TSU_ADD requests PTM to send the whole TS in sequence of 8 octets (64 bits). When those octets are beeing sent via TS_PTM port, TS_DV signal is set. All PPFTS pulses (see TSU_PTM and TSU_ADD doc) during this phase are counted by TSU_ADD and in the end they are added to the recieved TS. So TS value in TSU_ADD unit should be very close to that one in PTM.
• SHORT mode: TSU_ADD requests PTM to send the last octet of TS (7 downto 0). When this octet is beeing set on TS_PTM port, TS_DV signal is set. This mode differs from the FAST mode (see below). The last octet is sent via handshake.
• FAST mode: This mode is set as default, when neither INIT nor SHORT is set. During this mode PTM is sending the last octet of TS simultanously without acknoledgement. Higher octets of TS are beeing incremented by 1 when PPFTS pulse is noticed. So TS in TSU_ADD unit should be very close to that one in PTM.