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Broadway SPR Rules + Notes + Mini Guides + Misc Random Stuff - Vega - 05-15-2022
Broadway SPR Rules + Notes + Mini Guides + Misc Random Stuff
I have made this document when I needed a quick reference card to messing around with Broadways' special purpose registers. Might as well share it for anyone who needs it.
Sync and isync are synchronizing instructions. They play a huge role when modifying the Hardware Registers and certain other Special Purpose Registers.
Times when sync or isync are required~
1. sync is required BEFORE & AFTER clearing the L2E bit of the L2CR
2. isync is required BEFORE & AFTER modifying the ICE bit of HID0
3. isync is required BEFORE modifying ILOCK bit of HID0
4. sync is required BEFORE & AFTER modifying DCE bit of HID0**
5. sync is required BEFORE modifying DLOCK bit of HID0
6. isync is required AFTER any mtsr instruction when the segment registers effects an Instruction EA
7. isync is required AFTER any mtsrin instruction when the segment register(s) effects the Instruction EA
8. isync is required BEFORE & AFTER any mtsr instruction when the segment registers effect a Data EA
9. iysnc is required BEFORE & AFTER any mtsrin instruction when the segment registers effect a Data EA
10. sync is required BEFORE any modification to SDR1
11. isync is required AFTER any modification of SDR1
12. sync is required BEFORE modifying the POW bit of the MSR
13. isync is required AFTER modifying ANY of the following MSR bits....
POW, PR, ME, FP, SE, BE, IR, DR, RI, FE0, FE1
14. sync is required AFTER modifying the L2FM bit of HID4
15. sync is required AFTER reading the DMAQL bit(s) of HID2; you cannot write to these bits btw
16. sync is required AFTER writing the F bit high in the DMAL Register
17. isync is required AFTER writing to the IABR
18. sync is required AFTER writing to the DABR
19. isync is required AFTER modifying an IBAT Register***
20. isync is required BEFORE & AFTER modifying a DBAT Register****
21. isync is required BEFORE a tlbie instruction if the TLB effects Data
22. isync is required AFTER a tlbie instruction where the TLB effects Instructions
23. sync is required AFTER a tblie instruction if the TLB effects Data
24. tlbsync is required AFTER a TLB invalidation
***You can have multiple IBAT Registers be modified consecutively, with a single isync at the end.
****You can have multiple DBAT Registers be modified consecutively, with a single isync at the beginning & end
References for above isync/sync rules~
1. Broadway User Manual page 319.
2. Broadway User Manual page 137 for the 'BEFORE'. Broadway User Manual page 319 for the 'AFTER'
3. Broadway User Manual pages 60 & 137.
4. Broadway User Manual page 136 for the 'BEFORE'. Regarding the 'AFTER' there is no reference. Not mentioned in the Broadway manual but its a high probability since you are changing how Data Cache is executed.
5. Broadway User Manual pages 60 & 136.
6. PowerPC Microprocessor Family: The Programming Environments, table 2-23 (page 2-43)
7. PowerPC Microprocessor Family: The Programming Environments, table 2-23 (page 2-43)
8. PowerPC Microprocessor Family: The Programming Environments, table 2-22 (page 2-41)
9. PowerPC Microprocessor Family: The Programming Environments, table 2-22 (page 2-41)
10. PowerPC Microprocessor Family: The Programming Environments, table 2-22 (page 2-42)
11. PowerPC Microprocessor Family: The Programming Environments, table 2-22 (page 2-42)
12. Broadway User Manual page 330
13. POW Bit - Broadway User Manual page 330
13. PR Bit - Broadway User Manual page 89
13. All other bits: PowerPC Microprocessor Family: The Programming Environments, tables 2-22 & 2-23 (pages 2-41 & 2-43)
14. Broadway User Manual Page 66
15. Broadway User Manual Page 66
16. Broadway User Manual Page 324
17. Broadway User Manual Page 177
18. No reference. High probability. Since an isync is required for the IABR, it would make sense for a sync to be required for the DABR.
19. PowerPC Microprocessor Family: The Programming Environments, table 2-23 (page 2-43)
20. PowerPC Microprocessor Family: The Programming Environments, table 2-22 (page 2-42)
21. PowerPC Microprocessor Family: The Programming Environments, table 2-22 (page 2-42)
22. PowerPC Microprocessor Family: The Programming Environments, table 2-23 (pages 2-43 & 2-44)
23. PowerPC Microprocessor Family: The Programming Environments, table 2-23 (pages 2-43 & 2-44)
24. Broadway User Manual Page 180
NOTE: From everything I have read so far on the Broadway Manual & other PPC manuals, there is never a circumstance that ever requires a back-to-back sync nor a circumstance that ever requires a back-to-back isync.
Other HID0 bit rules:
1. Never have SGE bit on whenever the Write Pipe is enabled (reference: Broadway User Manual page 326)
HID2 bit rules:
1. The entire Instruction Cache must be disabled then invalidated before modifying the LSQE, PSE, and/or LCE bits. (reference: Broadway User Manual page 64)
HID4 rules:
You cannot modify any HID4 L2CR related bits while L2CR is on!
Bit 0 of HID4 must always be written as high (1), it will always read as 1 (reference: Broadway User Manual page 65).
Once bits 3 & 4 are set, its value cannot be lowered (reference: Broadway User Manual page 66)
Bit 3 & 4 settings:
00 = bus max depth of 2
01 = depth of 3
10 = depth of 4
11 = reserved/unused
Thus if the setting is 10, it cannot be changed at all.
The L2FM field (bits 1 & 2) follow this same rule, can also not be lowered once set (reference: Broadway User Manual page 66)
L2CR Mini Guides:
NOTE: Interrupts should always be masked (disabled) during any L2CR operations.
Following guides are referenced using Section 9.1.3 (Page 318), and Section 9.1.4 (Page 319) of the Broadway User Manual,
Guide for L2 Cache Global Invalidation:
*Interrupts must be masked (disabled) throughout this entire process
*DPM bit of HID0 must be low throughout this entire process
1. Disable the L2CR by setting the L2E bit low
2. Initiate the Global Invalidation by setting the L2I bit high #Steps 1 and 2 MUST be done separately!
3. Run a Loop that constantly checks the L2IP bit. Once that bit is low, the Invalidation has been completed.
Guide to Initialize L2CR:
*Interrupts must be masked (disabled) througout this entire process
*DPM bit of HID0 must be low throughout this entire process
1. Globally Invalidate the L2 Cache (see above guide)
2. Disable L1 instruction cache of HID0
3. Turn on the L2CR by setting the L2E bit high
4. Restore L1 instruction cache of HID0
Guide to Configure L2CR:
*Interrupts must be masked (disabled) throughout this entire process
*DPM bit of HID0 must be low throughout this entire process
1. Turn on the L2CR (see above guide)
2. Disable L1 instruction cache of HID0
3. Set L2CR L2DO bit high #example bit, can be a diff config bit of your choice
4. Restore L1 instruction cache of HID0
Guide to Turn off L2CR:
*Interrupt must be masked (disabled) throughout this entire process
1. Simply set the L2E bit low
*If you plan on invalidating or re-enabling L2CR after this, DPM bit in HID0 must be low before you start the invalidation or before you re-enable.
Guide to go into Reduced Power Mode (doze, nap, sleep)
*Interrupts must be ON! for the entire guide
1. Set Desired Power Mode bit high on HID0.
2. Flip POW bit high in the MSR (don't forget your sync before and isync after!)
3. Broadway will enter new power mode in a few clock cycles
Reference: Chapter 10.2 of the Broadway User Manual (pages 327 thru 330)
Reduced Power Mode options:
Doze: Time Base & Decrementer still work
Nap: Time Base & Decrementer still work
Sleep: Time Base & Decrementer do NOT work
You can get out of Doze and Nap mode by setting the Decrementer to the desired value before going into said power mode. Once Decrementer goes below 0, the Decrementer exception will run. Be sure to write some custom code in the Decrementer Exception to get you back to full power mode and back to normal operations.
Miscellaneous fun fact~
While in supervisor mode (MSR: PR bit low) any mtspr instruction involving HID1 or PVR will execute as a nop (reference Broadway User Manual page 90).