Data Corruption with Epyx Fast Load Cartridge on 1.24

[shferguson]

After upgrading from 1.23 to 1.24 on a Raspberry Pi 3B reads from the PI1541 on d64 images have sporadic data corruption when loading when the fast load cartridge is enabled. Without the cartridge programs are loaded correctly.

I loaded the "FB64" from the fb.d64 and dumped the first 0x4D bytes loaded and compared with and without the cartridge. A table of the differences is below.

I'd suspect that this is the cause of the issues reported in #215 and #233

Load Addr   No FastLoad   With Fast Load   Error
800         00            00
801         0B            0B
802         08            08
803         01            01
804         00            00
805         9E            9E
806         32            32
807         30            30
808         36            36
809         31            31
80A         00            00
80B         00            00
80C         00            00
80D         A9            A9
80E         05            05
80F         20            20
810         D2            D2
811         FF            FF
812         20            20
813         44            44
814         E5            E5
815         A4            A9              05
816         00            01              01
817         A2            A2            
818         00            00            
819         9D            9D            
81A         00            00            
81B         D8            D8            
81C         9D            9D            
81D         00            00            
81E         DE            D9              -05
81F         9C            9D              01
820         00            00            
821         DA            DA            
822         9D            9D            
823         00            00            
824         DB            DB            
825         CA            CA            
826         D0            D0            
827         F0            F1              01
828         A4            A9              05
829         06            06            
82A         8D            8D            
82B         20            20            
82C         D0            D0            
82D         A9            A0            
82E         00            00            
82F         8D            8D            
830         21            21            
831         D0            D0            
832         A5            A5            
833         BA            BA            
834         8D            8D            
835         01            01            
836         10            10            
837         A2            A2            
838         01            01            
839         20            20            
83A         99            99            
83B         0B            0B            
83C         A2            A2            
83D         17            17            
83E         20            20            
83F         99            99            
840         0B            0B            
841         A2            A2            
842         18            18            
843         A0            A0            
844         8A            1A              -70
844         16            18              02
846         20            20            
847         F0            F0            
848         FF            FF            
849         A0            A0            
84A         10            10            
84B         20            A9            
84C         1E            0C   

[dburr]

+1. Came here to report the exact same thing, and was glad to see this issue near the top of the issues page. Thought I was going crazy and/or that I made some sort of mistake while soldering up my Pi1541.

In my case, the data corruption isn't just sporadic, it is GUARANTEED 100% of the time if I have fastload enabled. If I disable fastload, everything works perfectly. Likewise, if I downgrade to 1.23, everything works perfectly, both with and without fastload enabled.

[lalcaraz]

Came here to say that v1.24 still not compatible with pi1541 for pi zero with fast load enabled. Using v1.23 is recommended.

[megatech1966]

Has the developer abandoned the pi1541. Haven’t seen a fix for 1.24. Not a sign of 1.25😢

[michaelrlowe]

I just ran across this issue on a Pi Model A+(Pi 1). It seemed to work just fine with the Fastload cartridge disabled, but corrupted frequently when it was enabled. After discovering this report I tried downgrading to 1.23 as suggested above. I downloaded the source and succefully built the 1.23 kernel with RASPPI ?= 1BPlus (same arch and GPIO pin count as the A+). The Pi booted and ran, but the problem was still present. Curious if it was a hardware problem, I switched to a Pi 2 and built a 1.24 kernel with RASPI ?= 2. That worked without any issue, so I concluded that it's probably not an problem with 1.24 specifically. More so probably with the older, slower Pi hardware, at least in my case. With 1.24 working I decided to try the Pi 1 again. In the config.txt I had the option arm_freq=1000. I remembered why that was there after I commented it out and it wouldn't boot. I retried with arm_freq=1100 and it started booting again. This time everything seems to be working as it should. With Fastload enabled I was now able to load programs that almost always corrupted on load before. Also worth noting, I'm now able to load and run some larger games that wouldn't load before even with the Fastload disabled. I had assumed the disk images were just broken, but it appears it was having timing issues with or without the Fastload. It just became much more noticable with Fastload enabled. So far that seems to have resolved the problem for me. Anyone running into this, even on newer Pi hardware, it may be worth the time to do some testing with the arm_freq value.