Add shadow register for UBRRH to keep it separate from UCSRC #309
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In e.g. ATmega8 UBRRH and UCSRC registers share the same I/O location.
Bit URSEL decides in which physical register written data should go.
As there are now more registers then I/O locations, "shadow" versions of
certain regbit functions that store to a pointer ("shadow register")
instead of the main registers in avr->data[] were introduced.
UBRRH was moved into a shadow register, while UCSRC stays a regular register.
Therefore, writes to UBRRH/UCSRC with URSEL bit set do not set the baudrate
falsely anymore.
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Thank You, I applied Your patch and working well. Great job. |
buserror
reviewed
Nov 27, 2019
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| if (addr == p->ubrrh.reg) { | ||
| if (p->ubrrh.reg == p->r_ucsrc) { | ||
| // UBRRH and UCSRC registers can share the same I/O location. | ||
| // URSEL bit decides which register gets written. If it's UBRRH, | ||
| // store to shadow register, else to regular register | ||
| if ((v & (1 << 7)) == 0) { // URSEL | ||
| avr_regbit_setto_shadow(avr, p->ubrrh, v, &p->ubrrh_shadow); | ||
| } else { | ||
| avr_core_watch_write(avr, addr, v); | ||
| } | ||
| } else { | ||
| // If UBRRH have different I/O locations, update shadow register and | ||
| // regular register | ||
| avr_core_watch_write(avr, addr, v); | ||
| avr_regbit_setto_shadow(avr, p->ubrrh, v, &p->ubrrh_shadow); | ||
| } | ||
| return; | ||
| } |
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I think that sort of behaviour should be encoded in the core declaration, for example a new field with 'ursel' would both allow feature testing and encode the feature in a generic way. here it's all hard coded.
Also for that sort of feature, I don't /think/ we really need the new _shadow accessors for regbits, it's a simple enough behaviour that is just visible in the set/get for this feature, AFAIK...
Personally, I would introduce a more generic behaviour where the two (or more) values are stored part of a regbit with a discriminant, instead of having to carry around a pointer to an uint8_t...
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In e.g. ATmega8 UBRRH and UCSRC registers share the same I/O location.
Bit URSEL decides in which physical register written data should go.
As there are now more registers then I/O locations, "shadow" versions of
certain regbit functions that store to a pointer ("shadow register")
instead of the main registers in avr->data[] were introduced.
UBRRH was moved into a shadow register, while UCSRC stays a regular register.
Therefore, writes to UBRRH/UCSRC with URSEL bit set do not set the baudrate
falsely anymore.