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authorhenryk <henryk@6dc7ffe9-61d6-0310-9af1-9938baff3ed1>2007-12-12 04:44:38 +0000
committerhenryk <henryk@6dc7ffe9-61d6-0310-9af1-9938baff3ed1>2007-12-12 04:44:38 +0000
commite777e32afb32f8863d495eff68ea0a91b0793fac (patch)
treea81dfdeb7211fc5ad4da5df06e1294f12b7ba724 /openpicc/os/boot/boot.s
parent202b56a42c5e6a171ee43b469be48525d0e8e350 (diff)
Add complicated mechanism that should have brought clock cycle accurate measurement. Doesn't seem to work properly
git-svn-id: https://svn.openpcd.org:2342/trunk@386 6dc7ffe9-61d6-0310-9af1-9938baff3ed1
Diffstat (limited to 'openpicc/os/boot/boot.s')
-rw-r--r--openpicc/os/boot/boot.s40
1 files changed, 37 insertions, 3 deletions
diff --git a/openpicc/os/boot/boot.s b/openpicc/os/boot/boot.s
index c065a6d..0371b6e 100644
--- a/openpicc/os/boot/boot.s
+++ b/openpicc/os/boot/boot.s
@@ -51,7 +51,7 @@
.equ SSC_CR, 0x0
.equ SSC_RCMR, 0x10
.equ SSC_CR_TXEN, 0x100
-.equ AT91C_TC_SWTRG, (1 << 2)
+.equ AT91C_TC_SWTRG, ((1 << 2)|1)
.equ AT91C_TC_CLKEN, (1 << 0)
.equ PIO_DATA, (1 << 27)
.equ PIO_FRAME, (1 << 20)
@@ -257,7 +257,7 @@ my_fiq_handler:
* At 47.923200 MHz 7 processor cycles are 2 carrier cycles of the 13.56MHz carrier
*/
.equ SUB_TIME, 20 /* subtract 20 carrier cycles == 70 processor cycles */
- .equ ADD_TIME, (70-20) /* Add x processor cycles */
+ .equ ADD_TIME, (70-30) /* Add x processor cycles */
mov r8, #SUB_TIME
sub r11, r11, r8
@@ -275,7 +275,41 @@ my_fiq_handler:
mov r11, r11, ASR #1 /* r11 = r11 / 2 */
mov r8, #ADD_TIME
- add r11, r11, r8 /* r11 = r11 + ADD_TIME */
+ adds r11, r11, r8 /* r11 = r11 + ADD_TIME */
+
+ bmi .wait_zero
+
+/* The following contraption is designed to compensate for the fact
+ that the loop below will only be able to count CPU cycles with a
+ precision of 4 cycles. Constraint: Since we want to keep the value
+ of r11 there's only one free register: r8.*/
+ mov r8, #0x1
+ tst r11, r8
+ beq .wait_zero_or_two
+ bne .wait_one_or_three
+
+/* relative timing ------+ All code paths have the same number of CPU cycles, except
+ V for the relative timing given in these comments */
+.wait_zero_or_two: /* +0 */
+ mov r8, #0x2
+ tst r11, r8
+ beq .wait_zero /* +0 */
+ nop
+ bne .wait_two /* +2 */
+
+.wait_one_or_three: /* +1 */
+ mov r8, #0x2
+ tst r11, r8
+ beq .wait_one /* +0 */
+ nop
+ bne .wait_three /* +2 */
+
+ nop /* Don't know if this nop is needed. Just add to make sure that nobody can assume that the "bne .wait_three" is no branch at all. */
+
+.wait_three:
+.wait_two:
+.wait_one:
+.wait_zero:
mov r11, r11, ASR #2 /* r11 = r11 / 4 (4 is the number of cycles per loop run below) */
personal git repositories of Harald Welte. Your mileage may vary