Secure NVM Read Service

Provides access to the data stored by the Secure NVM Write service or data programmed via a bitstream. If the data is programmed using authentication, the USK key used at the time of programming must also be provided.

Table 1. Secure NVM Read Request
System Service Descriptor Bit Field	Value	Description
15:7	MBOXADDR[10:2]	Mailbox address. See Table 2.
6:0	18H	Secure NVM Read service command

The following table lists the Secure NVM Read Service Mailbox Format (18H).

Table 2. Secure NVM Read Service Mailbox Format (18H)
Offset	Length (bytes)	Parameter	Direction	Description
0	1	SNVMADDR	Input	sNVM address
1	3	RESERVED	—	Reserved
4	12	USK	Input	User Secret Key (ignored if page is plaintext)
16	4	ADMIN	Output	Page admin data contains current write counter value, page type, and ROM flag. (see Table 3)
20	236 or 252	DATA	Output	Data read from sNVM. 236 bytes of data per page is available when the data is authenticated. 252 bytes of data per page is available when the data is not authenticated.

Table 3. sNVM Page Admin Data
Field	Offset	Size (bits)	Description
CYCLES	0	20	The current write counter for the page. Since there is no redundant copy, the counter cannot be guaranteed to survive a failed programming attempt.
PAGETYPE	20	2	Specifies how the DATA field is used. Each page may contain plaintext, authenticated plaintext, or authenticated ciphertext. See Table 4.
RESERVED	22	1	—
ROMFLAG	23	1	Specifies whether the page can be modified at runtime by the sNVM system services. If ‘1’, the page cannot be written by the sNVM system services.
UNUSED	24	8	—

Table 4. PAGETYPE and DATA
PAGETYPE	Offset	Size (bits)	DATA Usage	Description
0	—	—	Blank	Blank page
1	0	1888	CT	Authenticated and Encrypted
1	1888	128	SIVTAG	Authenticated and Encrypted
2	0	1888	PT	Authenticated Plaintext
2	1888	128	SIVTAG	Authenticated Plaintext
3	0	2016	PT	Plaintext

The page admin word (bits 31:0) is stored in ones-complement form. This is necessary to avoid a time consuming operation during zeroization to make the sNVM page look blank upon completion of zeroization.