54.5.8 SHA Bytes Count Register

Name:	SHA_BCR
Offset:	0x30
Reset:	0x00000000
Property:	Read/Write


Bit	31	30	29	28	27	26	25	24
	BYTCNT[31:24]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	23	22	21	20	19	18	17	16
	BYTCNT[23:16]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	15	14	13	12	11	10	9	8
	BYTCNT[15:8]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	7	6	5	4	3	2	1	0
	BYTCNT[7:0]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0

Bits 31:0 – BYTCNT[31:0] Remaining Byte Count Before Auto Padding

When the hash processing starts from the beginning of a message (without preprocessed hash part), BYTCNT must be written with the same value as MSGSIZE. If a part of the message has been already hashed and the hash does not start from the beginning, BYTCNT must be configured with the number of bytes remaining to process before the padding section.

When read, provides the size in bytes of the message remaining to be written before the automatic padding starts.

BYTCNT is automatically updated each time a write occurs in SHA_IDATARx and SHA_IODATARx.

When BYTCNT reaches 0, the MSGSIZE is converted into a bit count and appended at the end of the message after the padding, as described in the FIPS 180 specification.

To disable automatic padding, the MSGSIZE and BYTCNT fields must be written to 0.